From nano-to micro-particles of polysaccharide-silica composites through self-assembly and sol-gel processes

Chapter 6

From nano-to micro-particles of polysaccharide-silica composites through self-assembly and sol-gel processes Bruno Alonsoa and Emmanuel Belamiea, b a

Institut Charles Gerhardt de Montpellier, ICGM-MACS, UMR 5253 CNRS-ENSCM-UM, Montpellier Cedex 5, France; bEcole Pratique des

Hautes Etudes, PSL Research University, Paris, France

Nomenclature list AFM Atomic force microscopy CNC Cellulose nanocrystals CNF Cellulose nanofibers CP-MAS Cross-Polarization Magic Angle Spinning DMT Derjaguin-Muller-Toporov EISA Evaporation Induced Self-Assembly NMR Nuclear Magnetic Resonance POM Polarized optical microscopy QNM Quantitative nanomechanical mapping SAXS Small Angle X-ray Scattering SEM Scanning electron microscopy TEM Transmission electron microscopy TEMPO 2,2,6,6-Tetramethylpiperidine-1-oxyl radical TEOS Tetraethoxysilane (or Tetraethyl orthosilicate) TMOS Tetramethoxysilane (or Tetramethyl orthosilicate) XRD X-Ray Diffraction fCEL Cellulose volume fraction fCHI Chitin volume fraction

6.1 Introduction Healthcare, energy and environmental issues have sparked interest in safer and greener routes for the synthesis of materials. This led to the development some decades ago of “chimie douce” approaches like sol-gel chemistry [1e3], and more recently to green chemistry and bio-inspired strategies [4e6]. In parallel, the advances in the synthesis and characterization of materials defined at the nanometer scale represent a great opportunity for innovation in chemistry and pharmaceutics. These nanoscale approaches spread over a wide range of fields, and naturally in sol-gel and green chemistry including selfassembly processes [7e10]. Within this context, the formation of hybrid organic-inorganic materials using polysaccharides nano-objects and oxide-based colloids is a very active research axis. In this chapter, we focus mostly on microparticles of polysaccharide-silica composites obtained from colloidal suspensions through self-assembly and sol-gel processes, and which characteristics and properties are related to polysaccharides and oxide phases possessing at least one dimension defined at the nanometer scale. Therefore, the use of preformed polysaccharide networks as templates that leads to interesting materials and insights on bio-mineralization [11e19] is out of the scope of this chapter. Readers interested in these topics are referred to the above cited and

Biocompatible Hybrid Oxide Nanoparticles for Human Health. https://doi.org/10.1016/B978-0-12-815875-3.00006-0 Copyright © 2019 Elsevier Inc. All rights reserved.

87

88

PART | II Biotechnology and biomedicine

related references. Also excluded are the works dealing with polymer reinforcement through the incorporation of colloids - polysaccharides, inorganic particles - as fillers, or by the molecular functionalization of these colloids. Some of the topics covered by this chapter have previously been reviewed elsewhere [20e27]. We have tried to present a comprehensive review of past and recent studies within the specific scope of this chapter, and based on our experience in the field. We apologize for any eventual omission of relevant works, mostly due to the terminology employed and to the diversity of approaches in this growing field. In the following, we overview the main characteristics (synthesis, characterization, properties) of the polysaccharidesilica composites considered. In a first section, we present how polysaccharide nanorods and nanosized inorganic precursors (e.g. siloxane oligomers) can be assembled to form hybrid nanocomposites. This includes basic information on polysaccharide (chitin, cellulose) nanorods structure and properties and a description of different approaches proposed to elaborate hybrid materials. The section also comprises a description of present strategies applied to tailor and modulate the final morphology with specific sol-gel processes. The next section concerns the means investigated to orient the textures in the hybrid nanocomposites by taking benefit of the susceptibility of polysaccharide nanorods mesophases to external fields. In a third section, we focus on the control of the morphology of the nanocomposites and related mesoporous silica using spray-drying processes. The final section presents two families of mesoporous microparticles of different inorganic composition (alumina, silica-titania) elaborated with the same sol-gel and self-assembly approaches. The potentiality and flexibility of this innovative colloid-based synthesis route is then illustrated with a specific application in heterogeneous catalysis.

6.2 Colloidal assembly of polysaccharide nanorods and siloxane oligomers 6.2.1 Polysaccharide nanorods Polysaccharide nanoparticles can be extracted from many biological tissues where they constitute major structural units. In particular, cellulose and chitin semi-crystalline nanorods are readily obtained from biomass, respectively arthropods’ cuticle and plant cell walls. In both cases, the elongated crystalline particles are described as being connected by amorphous domains. Most extraction procedures rely on the preferential cleavage of these disordered, more accessible regions, principally by hydrolysis or oxidation. Relatively harsh treatments allow for the separation and dispersion of individual e or small bundles of e nanorods [28e31]. The high aspect ratio of such polysaccharide nanoparticles confers specific properties to the colloidal dispersions of these particles. Such high shape anisotropy also results in peculiar structural features and properties in the composite materials prepared with these nanorods (see Section 6.2.3). Chitin is a highly abundant natural polymer and is the main organic constituent in the cuticle of arthropods like crustaceans and insects. Most often, chitin nanocrystals are prepared from crustacean shells available in very large amounts as a by-product of the fishing industry. Typically, shrimp shells are first demineralized and deproteinized before applying the treatments to isolate crystalline nanorods. Separation of the crystalline domains to prepare suspensions of nanorods is usually achieved by acid hydrolysis [28e31], although alternative methods based on mechanical or oxidative treatments have been developed recently [32e34]. Because the raw chitin product is comprised of powdered semi-crystalline material, acid hydrolysis occurs in heterogeneous conditions and preferably attacks the disordered domains (Fig. 6.1). This results in the longitudinal fragmentation of elongated crystals, and partial lateral disaggregation produces small bundles of monocrystals further dispersed with ultrasounds. These chitin nanorods, or whiskers, have rather polydisperse dimensions depending upon biological sources and preparation procedures (Fig. 6.2), typically between 200 and 500 nm in length and between 10 and 50 nm in diameter, with an aspect ratio L/D of approximately 10e15 [35]. Nanofibers approximately 10e20 nm wide can also be prepared by grinding in much milder conditions [36], dispersed as aqueous slurries and used to elaborate nanostructured membranes [37] and hybrid fibers [38]. However, in what follows, we will principally describe the properties of acid-hydrolyzed nanoparticles and their use for materials preparation. Cellulose nanorods, often termed whiskers or nanocrystals (CNC) can be prepared in a very similar manner from different vegetal sources [39]. As for chitin, acid hydrolysis is by far the most widely used process to isolate crystalline cellulose nanorods [40], as popularized by the work of Marchessault and co-workers [28,41]. The dimensions of the extracted CNC can largely vary depending on the cellulose source (bacteria, cotton, ramie, algae .) [39] and hydrolysis conditions [42,43]. For instance, cellulose whiskers extracted from the algae Valonia have an almost square section 5e10 nm wide [44,45], while those from another algae Micasterias are described as flat twisted ribbons with a rectangular cross section [46] up to 60 nm wide [47]. The extraction steps involving acid hydrolysis, apart from providing nanometer-sized particles, also result in the introduction of ionizable groups at the outer surface of the nanorods. In the case of cellulose, the use of sulfuric acid for

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

(A)

O HO NH O

O HO

HO OH H

HO O O

O N NH

O

O HO

HO O O

HO OH

(B)

89

Chitin

OH

Cellulose

(C)

FIG. 6.1 Schematic of (A) the chitin and cellulose repeating units, (B) idealized cellulose microfibrils with the proposed alternation of crystalline and disordered domains, and (C) cellulose nanocrystals obtained after chemical treatment and removal of amorphous regions. (BeC) Reproduced from Moon et al., Chem. Soc. Rev. 2011;40:3941e94 with permission of The Royal Society of Chemistry.

FIG. 6.2 Transmission electron micrographs of a-chitin whiskers extracted from crab shells by acid hydrolysis (A) or TEMPO-mediated oxidation (B), and b-chitin nanofibers prepared from squid pen by mechanical disintegration (C). Reprinted with permission from (A) Belamie, et al. J Phys Chem B 2004;108:14991e1500, (B) Fan, et al. Biomacromolecules 2008;9:192e8, (C) Fan, et al. Biomacromolecules 2008;9:1919e23. Copyright 2004 and 2008 American Chemical Society.

instance yields negatively charged sulfate groups. In contrast, chitin submitted to harsh acidic treatment is partially deacetylated, yielding amino groups which can be ionized at acidic pH to produce positive charges. The particles’ surface charges, positive or negative, accounts for their colloidal stability when suspended in aqueous media. Owing to their strong shape anisotropy, chitin and cellulose nanorods exhibit remarkable proprieties, among which the ability to form liquid crystal phases beyond a critical volume fraction [29e31,48e50]. In the obtained lyotropic nematic mesophases, the elongated polysaccharide particles are evenly distributed with interparticle distances in the 10e100 nm range and locally aligned along the same direction. The nematic mesophases formed by chitin and cellulose nanorods are chiral (cholesteric), which means that the main direction of the locally aligned rods rotates regularly, thus resulting in a long-range helical organization. It is worth noticing that this long-range helical structure of the liquid with typical pitch values in the 1e100 mm range is reminiscent of the periodical helical structure described in the corresponding biological tissues like plant cell walls (cellulose) and arthropods cuticles (chitin) [51e56]. Studies of the structure and properties of these helically organized biological materials have been largely reported and the reader is invited to refer to review articles on these specific aspects [57e61]. In several biological tissues like crustacean shells or sponge spicules, a mineral phase

90

PART | II Biotechnology and biomedicine

(calcium carbonate or silica) reinforces the organic matrix comprised of polysaccharide nanocrystals [5,62]. The ability of polysaccharide nanorods, extracted and dispersed as colloidal suspensions, to form cholesteric liquid crystals gives an opportunity to elaborate bio-inspired nanocomposites in association with inorganic phases of potential interest for applicative purposes.

6.2.2 Different approaches for the synthesis of nanostructured polysaccharide-oxide materials Several approaches have been proposed to elaborate hybrid silica-based nanocomposites from crystalline polysaccharide colloids, tentatively classified in three main types: -

The “nematic phase replication” based on the manipulation of liquid crystal mesophases, either preformed and impregnated or induced by the condensation of the inorganic network. The “co-assembly” approach consisting in the mixture of both types of colloids, polysaccharide and inorganic. The use of “hybrid colloids” already containing both polysaccharide and inorganic moieties.

6.2.2.1 Nematic phase replication Following a previous work on the mineralization of Tobacco mosaic virus liquid crystals [63], Mann and co-workers first proposed in 2003 the formation of mesoporous silica as replicas of cellulose crystalline nanorods’ nematic suspensions [64]. Birefringent solids were obtained after solvent evaporation from a mixture of pre-hydrolyzed tetramethoxysilane (TMOS) and a cellulose nanorods mesophase. The birefringence was preserved after calcination and helical structures were observed locally by TEM. In 2010, MacLachlan et al. investigated an alternative method starting from an isotropic suspension of cellulose nanorods combined with silicon alkoxide precursors (TMOS or tetraethoxysilane TEOS) and forming a chiral nematic phase upon solvent evaporation. This phase was well preserved after complete drying, and even after calcination leading to free-standing iridescent mesoporous silica films. The mechanical or optical properties were varied by changing the alkoxide precursors [65], the self-assembly conditions [66,67] or by post-modification of the resulting films [68e70].

6.2.2.2 Colloidal co-assembly An alternative approach consists in mixing together polysaccharide colloids’ suspensions with organometallic colloids’ sols to form stable co-suspensions that can be processed into a variety of materials with contrasted shapes, textures and compositions. In 2010, we proposed this approach for the formation of chitin-silica nanocomposites [71]. Further, mesoporous silica materials with elongated pores defined by the dimensions of the chitin nanocrystals (D z 2e3 nm) were obtained by calcination in air [71,72]. A wide range of morphologies can be achieved for this family of nanocomposites with standard sol-gel processes: thin films by dip- or spin-coating, cast films, microspheres by spray-drying, microfibers by electrospinning. This approach is exposed in more details in the next Section 6.2.2.3.

6.2.2.3 Hybrid colloids In some of the studies cited above, we and others noted that a silica shell formed around individual polysaccharide (chitin and cellulose) monocrystals [71e74]. This and later observations pointed out the possible formation of hybrid colloids during processing. Zollfranck and co-workers published in 2009 the synthesis of silica nanotubes obtained coating cellulose whiskers with silica followed by calcination [75]. The dense silica nanowires obtained after treatment at high temperature (900
C) could be further decorated using small gold nanoparticles (2e6 nm in size) as seeds [76]. Besides, Buskens et al. used CNC coated by silica as hybrid colloids for the formation by dip-coating of thin films with disordered textures. Further removal of cellulose by calcination yielded porous silica layers with low refractive index (n  1.1) [77]. More complex hybrid colloids can be synthesized for specific properties. For example, Tam and co-workers elaborated nanorods made of CNC decorated with Fe3O4 nanoparticles, then covered by a silica layer (thickness from 6 to 14 nm) that is further functionalized with b-cyclodextrin groups [78]. This multi-step procedure allowed the authors to form magnetic particles with interesting adsorption properties toward organic drugs (procaine hydrochloride and imipramine hydrochloride).

6.2.3 Chitin- and cellulose-silica nanocomposites from colloidal co-assembly Following an approach involving polysaccharide and inorganic colloidal precursors as shortly presented in Section 6.2.2.2, we proposed a new synthesis route for the elaboration of nanocomposites [71]. Initially, an ethanolic co-suspension of

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

91

preformed siloxane oligomers (Dh z 3 nm, dcondensation z 0.75) and chitin nanorods (L z 260 nm, D z 23 nm) was achieved by mixing together both colloids and replacing residual water by ethanol. At moderate chitin concentrations (below ca. 1 wt%), the co-suspension appeared stable for weeks in contrast with water-containing suspensions subjected to relatively fast kinetic processes. Therefore, this co-suspension can be used to form materials in large amounts after ethanol evaporation and completion of the siloxane hydrolysis and condensation reactions (typically with water molecules from air moisture). As stated in Section 6.2.1, chitin and cellulose nanorods in suspension form liquid crystalline phases when brought above a critical concentration. This propriety was also noted for the hybrid colloidal mixtures. Upon evaporation of the solvent, the colloidal chitin-silica suspension showed a marked increase in viscosity accompanied by a gradual rise in optical birefringence. After complete evaporation of the solvent and consolidation of the solid by extensive silica condensation (dcondensation z 0.9), the resulting hybrid materials exhibit a final silica/chitin composition which corresponds very closely to their initial proportions in the suspension. We defined the proportion of chitin (or in general crystalline polysaccharide) in the solid fPOLYSACH as its volume fraction in the final solid: fPOLYSAC ¼

VPOLYSAC VPOLYSAC þ VSiO2

(In what follow, fCHI and fCEL are used for chitin and cellulose suspensions respectively). This parameter was further used to describe the suspensions composition, along with the total weight concentration. High fPOLYSACH therefore means low silica content, while at values below fPOLYSACH ¼ 0.5 silica is in excess. In bulk materials, after slow evaporation of the solvent (ethanol) the polycrystalline chitin nanorods were preserved and welldispersed in the final siloxane network as visible by TEM on ultrathin sections. Electron microscope observations also reveal that the silica network is associated with the polysaccharide nanoparticles at the level of individual monocrystals, which implies that the oligomers were able to diffuse through the amorphous domains (see Section 6.2.1) holding together the bundles. It is noteworthy that this intimate association between siloxane oligomers and the nanocrystals surface was also evidenced in materials processed with techniques based on fast solvent evaporation, such as electrospinning (to be published), spin coating [79,80] or spray drying [71]. Hybrid materials processed by spray-drying as chitinesilica microparticles have an overall spheroid shape (Fig. 6.3, C) and mean diameters in the 2.2e2.5 mm range. Increasing fCHI resulted in a visible roughening of the particle surface, with elongated rods having dimensions (D ¼ 26  6 nm, L ¼ 240  45 nm) very close to those of the extracted chitin nanorods, separated by voids (10e100 nm) visible at high fCHI. This suggests that the polysaccharide nanorods are coated by siloxane oligomers to form hybrid rods. Importantly, inspection of the hybrid and calcined solids by electron microscopy (SEM, TEM) demonstrated that the silica phase forms a coating around the chitin nanocrystals constituting the chitin nanorods (Fig. 6.4). This and later observations pointed out the possible formation of hybrid colloids during processing. Surprisingly, despite opposite surface charges (negative sulfate groups for cellulose whiskers and positive amine groups for chitin nanocrystals) very similar results were obtained when using cellulose nanocrystals instead of chitin [81]. The dimensions of the spray-dried particles were about the same (2.2e2.7 mm in diameter) and the surface roughness also increased with increasing fPOLYSACH (Fig. 6.3, A-B). As observed with chitin, the porous features after calcination of the organic moiety suggested direct templating of the polysaccharide monocrystals by silica at the monocrystal level.

(A)

(B)

(C)

FIG. 6.3 SEM micrographs of spray-dried microparticles. (A and B) Cellulose-silica nanocomposites with increasing cellulose volume fraction fCEL (0.29, 0.64). (C) Chitin-silica nanocomposites (fCHI ¼ 0.64). The scale bars correspond to 2 mm. Reproduced from Cardoso, et al. New J Chem 2017;41:6014e24 with permission from the Center National de la Recherche Scientifique (CNRS) and The Royal Society of Chemistry.

92

PART | II Biotechnology and biomedicine

(A)

(B)

(C)

FIG. 6.4 Electron Microscopy observations of spray-dried chitin-silica nanocomposites (A) and calcined silica replica (B and C). SEM observations (A and B) show the surface roughness due to the entanglement of elongated rods. The TEM analysis on a calcined sample (C) shows entangled rods of silica separated by voids (10e100 nm) and the imprint of the chitin monocrystals (2e3 nm wide) (black arrows in the zoomed area). Adapted with permission from Alonso and Belamie, Angew Chem Int Ed 2010;49:8201e4.

Therefore, both chitin and cellulose nanoparticles appear to interact strongly with siloxane oligomer regardless of the surface charge, which suggests the dominant role of the high density of hydroxyl groups on the sugar cycles. In our work with cellulose or chitin nanocrystals as organic precursors in colloidal association with siloxane oligomers [81], we investigated more closely the organic-inorganic interface by seeking possible changes in the structure of the polysaccharide phase in nanocomposite materials. Structural analysis by solid-state NMR and XRD showed no critical changes in both polysaccharides crystalline structures but minute modifications of X-ray diffractograms and 13C NMR spectra were visible. More precisely, diffraction peaks characteristic of Ib cellulose were shifted toward higher diffraction angles when comparing celluloseesilica nanocomposites to spray-dried pure cellulose crystals. And the shift slightly increased with decreasing fCEL (increasing silica content). The decrease in d200 with increasing silica content (decrease of fCEL) corresponded to a decrease in the a cell parameter that could reach about 2% for the samples containing the smallest cellulose amount. Similar values have been found for the b cell parameter and the same trend was also observed for the a and b cell

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

93

parameters of chitinesilica nanocomposites. Although these variations are small, they reveal a possible contraction of the polysaccharide crystal under the effect of the siloxane condensation at its surface, and this contraction is larger when the silica content increases. Further structural analysis by 13C{1H} NMR CP-MAS revealing a shift of the 13C signals of cellulose are consistent with the above observations. In summary, this set of data [81] along with previous microscopic observations [71,72] highlight strong interactions between the colloidal inorganic species and polysaccharide nanocrystals surfaces. Strong interactions between the organic and inorganic precursors were also evidenced by rheological investigations [82]. In our recent study we demonstrate that in spite of a lower dissociating power of ethanol compared to the more common aqueous media, repulsive interactions between the chitin nanoparticles charged surface, in absence or presence of siloxane oligomers, provide good colloidal stability to the suspensions. Most importantly, chitin nanorods and siloxane oligomers interact in ethanol suspensions as reflected by major changes in rheological behavior occurring for a critical fCHI  0.3 consistent with the complete coverage of the chitin surface by siloxane oligomers. In fact a simple geometrical estimation [71] showed that complete coverage of the monocrystals surface would occur for fCHI values in the 0.2e0.4 range. Although this is a very rough estimate, it agrees well with several experimental observations such as TEM [71], porous properties of the calcined replicas [72], nanomechanical characterization by AFM [79,80] and the abovementioned rheological study to name a few. This again agrees well with the hypothesis of a close interaction between the siloxane oligomers and the polysaccharide surface in the hybrid suspensions.

6.2.4 Morphology variations through sol-gel processing The colloidal co-assembly approach described above (Sections 6.2.2 and 6.2.3) allows for the formation of stable co-suspensions containing polysaccharide nanorods and nanosized inorganic precursors like the siloxane oligomers considered until now. The inorganic precursors act here as building blocks with a reactive shell and a pre-condensed core. These stable suspensions can be used directly to form hybrid nano-composites with specific morphology and texture. Indeed, when the colloids concentration is increased (e.g., by solvent evaporation), and/or when reactive molecules are introduced (e.g., water coming from moisture), the covalent bonding between these building blocks is promoted through condensation reaction schemes. The sol-gel transition and the further solidification of hybrid polysaccharide-oxide composites can then occur [2,3]. Therefore, all processes allowing to shape materials under drying conditions are of interest for controlling the final organization of the composites. Some examples are presented in Fig. 6.5. In addition to the opportunities offered by these shaped materials toward specific applications (e.g., for heterogeneous catalysis, Section 6.5), the study of the different morphology brings interesting insights into the co-assembly approach. For

FIG. 6.5 The stable co-suspensions containing polysaccharide nanorods and inorganic colloid precursors can be processed into nano-composites with specific morphology and texture.

94

PART | II Biotechnology and biomedicine

instance, thin films of chitin-silica nano-composites (thickness z 100e200 nm) were obtained through spin-coating, and further analyzed by AFM techniques [79,80]. The variations in the mechanical properties as a function of fCHI were probed at the nanoscale using the PeakForce QNM mode [80]. It was shown that the DMT modulus (5e40 GPa) and the surface roughness (4e12 nm) are closely related to the formation and assembly of hybrid chitin-silica nanorods (D z 30 nm). Similar rods were observed at the surface of spray-dried chitin-silica microparticles (D z 30 nm) for the highest fCHI values (see Section 6.2.3) [71,81]. Also, the assembly of these rods during electro-spinning yielded nanofibers (100 nme1 mm) with chitin crystals oriented along the main axis. Taken together, these studies point to the formation of hybrid colloids, consisting in chitin-silica nanorods, before or during the solvent evaporation steps of the sol-gel processing (vide supra).

6.3 Opportunities for texture orientation with external fields As explained above, chitin and cellulose nanorods having a high aspect ratio form liquid crystal phases beyond a critical volume fraction. This entropy-driven isotropic/nematic first-order transition is associated with a sharp increase of the order parameter [48,83] and the apparition of strong optical birefringence. Most often, suspensions of unmodified polysaccharide nanocrystals are prepared in aqueous media but other polar solvents have also been used successfully [71,84e88]. High permittivity solvents were shown to enhance self-assembly, notably influencing the dynamics and equilibrium structural values [88]. Concentrated suspensions of both crystalline polysaccharide rods strongly respond to the application of external fields such as shearing, electric and magnetic fields because of coorperative effects. Flow-induced birefringence and phase alignment was noticed in early studies [28] and later investigated by optical measurements and small angle neutron and X-ray scattering analyses [31,89,90]. Owing to this susceptibility of the nanocrystals suspensions, we investigated the opportunities of manipulating the texture of nanocomposites using external fields.

6.3.1 Electric field Dispersed cellulose whiskers were shown to align parallel to the direction of an applied electric field [91]. As a consequence, the helical texture of both chitin and cellulose chiral nematic phases was shown to unwind in an electric field producing uniaxially aligned nematic phases, although the origin of the force inducing the alignment is presumably different [92,93]. We also recently reported that anisotropic chitin tactoids submitted to an electric field reorient quickly (<1 s) and then highly deform (100e1000 s) along the direction of the field [94]. Hybrid suspensions of chitin and siloxane oligomers were thus submitted to high frequency AC voltage (up to 400 V) with the aim of producing uniaxially aligned nanocomposites [93]. Anisotropic chitin-siloxane co-suspensions responded strongly with the effective order parameter reaching 0.75 in a matter of seconds (Fig. 6.6A), which corresponds to values typically expected for such nematic liquid crystals [48,50]. Interestingly, the suspension did not relax after the field was switched off and the alignment was maintained for several days. In contrast, isotropic suspensions also responded quickly to the application of the field but the alignment was lost almost immediately after removing the field (Fig. 6.6B). The persistence of the field-induced alignment of anisotropic suspensions was exploited to obtain oriented nanocomposites after complete evaporation of the solvent outside the field. The resulting solid gave an anisotropic SAXS pattern, due to an oriented texture from which an order parameter of w 0.32 was determined. Similarly, polarized optical microscopy (POM), SEM and TEM observations revealed the long-range uniform alignment of elongated particles along the direction of the field. This shows that the initial electric field-induced alignment was partly preserved during the solgel transition and further solidification due to solvent evaporation and siloxane condensation, yielding aligned chitinsilica nanocomposite materials.

6.3.2 Magnetic field In contrast to the uniaxial alignment along the direction of an electric field, cellulose and chitin rodlike particles align perpendicular to the direction of a magnetic field, which has been attributed to negative diamagnetic anisotropy in a study with tunicate cellulose whiskers [95]. One consequence is that the chiral liquid crystal reorients with its cholesteric helical axis parallel to the direction of the applied magnetic field [31,89,96e98]. It was recently demonstrated that cellulose nanorods suspensions could be aligned in relatively weak magnetic fields. This was only possible thanks to strong cooperative effects occurring above the critical concentration of the isotropic-nematic transition [99]. Co-suspensions of chitin nanorods and siloxane oligomers in ethanol were submitted to a strong magnetic field B of 9.4 T. By keeping the samples in the field throughout solvent evaporation and across the sol-gel transition, the resulting

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

95

FIG. 6.6 SAXS patterns (left images) and evolution of the order parameter (right graphs) for anisotropic (A) and isotropic (B) chitin nanorod siloxane oligomers hybrid suspension submitted to an electric field (140 V mm1 r.m.s.). The suspensions were prepared in ethanol/aqueous 104 M HCl mixtures (50/50 wt%). The chitin concentrations are 5.0 wt% and 2.0 wt% for the anisotropic and isotropic suspensions respectively. The direction of the field with respect to the SAXS patterns is indicated by the black arrow. The dashed lines in the graphs are a guide to the eye. Adapted with permission from Boltoeva, et al. Langmuir 2013;29:8208e12. Copyright 2013 American Chemical Society.

materials showed homogenous alignment of the chitin nanorods perpendicular to B. The uniaxial alignment of the nanocomposite was studied by polarized light microscopy, which revealed the uniform orientation of the nematic director over several centimeters. We assessed the direction of the nematic director with respect to the electric field by determining the sign of the birefringence using a first order l retardation plate. This orientation was maintained after calcination of the chitin as also demonstrated by POM and by the presence of aligned elongated porous structures visible by TEM [71].

6.4 Control of morphology and pore texture in calcined replicas 6.4.1 Spray-dried templated mesoporous materials At the beginning of the 19900 , a new field of research emerged after Mobil researchers had shown that ordered patterns of mesopores (2 < Dpore < 50 nm) can be formed in oxide materials using micellar assemblies [100]. This breakthrough led to a huge number of publications (the first article has been cited more than 12,500 times), and several innovations in the synthesis and applications of mesoporous materials [101e105]. One interesting feature of the developed synthesis’ routes is the effective tuning of the pore texture (pore dimensions and spatial organization) by a rational use of templates like micelles, liquid crystals, synthetic polymers, other porous materials, and, more related to this chapter, biological nanoobjects [26,106e109]. Another interesting feature is the possible combination of these templating approaches with sol-gel chemistry. This allows reaching a wide range of chemical compositions. In addition, it facilitates the getting of mesoporous materials with specific morphology through the use of well-known processing setups like: thin films by dip- or spin-coating, micro- or nano-fibers by electrospinning and microparticles by spray-drying (Section 6.2.4). Spray-drying techniques [110] are efficient approaches to obtain mesoporous microspheres or spheroid microparticles [111,112]. It was demonstrated that drying an aerosol of micrometer sized droplets containing a diluted solution of surfactants and siloxane oligomers can lead to nanometer and/or micrometer sized mesoporous silica spheres [113,114]. The formation of micelles and further the hybrid organic-inorganic mesophases are promoted when the concentrations of the reactive species increase due to the continuous evaporation of solvent (typically water and ethanol), and in particular when the quantity of surfactants is above the critical micelle concentration. This approach was named Evaporation Induced Self-Assembly (EISA) [7] and has been successfully applied to obtain mesoporous materials with specific morphology.

96

PART | II Biotechnology and biomedicine

The mechanism of formation of mesoporous microparticles through EISA and the role of the various parameters determining the final properties have been deeply investigated [114e118]. It appears of paramount importance in these syntheses to control the rate of the different physico-chemical processes occurring at different length scales: transfers of matter and heat through the air-liquid interfaces and inside the droplets, micellization and ordering of surfactant assemblies, droplet fragmentation and agglomeration, sol-gel transition and further droplet solidification. This knowledge, along with empirical experimentations, allowed to expand the type of synthesized materials, and, to name a few applications and works, the formation of other oxide phases than silica [119e122], the location at the pore surface of several functionalities among which specific organic groups (Me, Ph, SH, PO3H2, .) [123e126], and the encapsulation of magnetic nanoparticles, drugs and other active objects, in the bulk or in the porosity of the microparticles [127e130].

6.4.2 Mesoporous silica microparticles through nanopolysaccharide templating Mesoporous silica microparticles can be obtained by simply extracting or calcining the biopolymer present in spray-dried polysaccharide-oxide nanocomposites prepared from ethanolic suspensions through a co-assembly approach. A main advantage of this approach is its increased robustness compared to the EISA. Indeed, no micellization is needed, the pores have calibrated diameters related to the diameters of the polysaccharide nanorods or nanocrystals and the extent of porosity can be simply controlled by varying the initial polysaccharide content (vide infra). Furthermore, the possible formation of hybrid colloids allows to locate specific functionalities at the final pore surface by playing with the surface chemistry of the polysaccharide nanorods (Section 6.2.1). In order to investigate the nature of the pore textures formed, we have undertaken a systematic study of porous silica materials obtained by calcining bulk chitin-silica nano-composites [72]. Whatever the initial chitin volume fraction fCHI (range explored: 0.0 < fCHI < 0.7), the nitrogen sorption isotherms (T ¼ 77 K) always present a hysteresis loop related to the capillary condensation in mesopores. Besides, microporosity is limited to a low extent (below 3%). The pore volume (0e550 109 m3 g1) and the specific surface area (0e400 m2 g1) derived from these N2 sorption isotherms gradually increase with fCHI. We also noticed that the diameters of the elongated mesopores measured by TEM analyses or estimated from the isotherms take values (Dpore z 3e5 nm) very close to the diameters of the monocrystals forming the chitin nanorods (D z 2e3 nm). All together, this information demonstrates that the mesoporosity is originating from chitin nanorods’ imprints. Interestingly, the distribution of mesopores (or chitin imprints) depends on the pore volume fraction fPOR (and the related fCHI) and mimics the chitin nanorods’ assemblies observed in water suspensions (Figs. 6.7 and 6.8). Three composition domains can be defined in relation with a critical value for the pore volume fraction fPOR* z 0.3 (and a

FIG. 6.7 Pore volume fraction fPOR as a function of initial chitin volume fraction fCHI. The TEM pictures correspond to the typical textures observed for the different fCHI domains (AeC). Adapted from Belamie, et al., J Mater Chem 2011;21:16997e17006 with permission from The Royal Society of Chemistry.

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

97

FIG. 6.8 Schematic representation of the pore textures as a function of the pore volume fraction fPOR (directly related to the chitin volume fraction fCHI). Reproduced from Belamie, et al. J Mater Chem 2011;21:16997e17006 with permission from The Royal Society of Chemistry.

related fCHI* in the range 0.2e0.4): (A) fPOR < fPOR*, the mesoporosity corresponds to chitin nanorods’ imprints distributed in an excess of silica; (B) fPOR z fPOR*, ordered textures of calibrated mesopores; (C) fPOR > fPOR*, the mesoporosity is less ordered and regular due to nanorods’ entanglements and to an incomplete coating of the chitin monocrystals by silica. By spray-drying, pore textures with almost the same fPOR (fCHI) dependence can be obtained inside spheroid microparticles [71,81]. The particle size distribution is not affected by the variations in fCHI while the surface roughness does (Fig. 6.9). In particular, at the highest fCHI values, the roughness increases due to the excess of chitin nanorods (relative to

FIG. 6.9 Morphology variations as a function of initial chitin volume fraction fCHI for spray-dried mesoporous silica particles. The scale bar in SEM pictures is 1 mm. The graph represents the four size distributions obtained by light scattering granulometry on the samples studied by SEM. Adapted with permission from Alonso and Belamie, Angew Chem Int Ed 2010;49:8201e4.

98

PART | II Biotechnology and biomedicine

silica). The voids between silica rods (imprints of chitin nanorods) create thus a supplementary porosity in mesopore/ macropore range. These results obtained from chitin-silica nanocomposites were translated to the cellulose-silica system [81]. We have replaced chitin nanorods (Lrods ¼ 260  80 nm; Drods ¼ 23  3 nm; Dmonocryst. z 3 nm) by cellulose nanorods (Lrods ¼ 130  50 nm; Drods ¼ 25  15 nm; Dmonocryst. z 6 nm) in the initial ethanolic suspensions containing the same distribution of siloxane oligomers. Although the surface chemistry of both polysaccharide nanorods differs (amino groups for chitin, residual sulfato groups for cellulose), we found the same trends for the spray-dried mesoporous silica particles (see discussion in Section 6.2.3). Moreover, the differences in specific surface area and pore diameters (z3e5 nm and z4e7 nm for chitin and cellulose precursors respectively) can easily be explained by the differences in monocrystals’ diameters. Therefore, the synthetic procedure described herein allows tuning the porosity of spray-dried mesoporous silica particles in different ways by playing either on the relative quantity or on the dimensions of polysaccharide nanorods. Besides, the specific surface chemistry of the rods (e.g., chitin vs. cellulose) can be exploited to functionalize the pore surface.

6.5 Functionalized surfaces and improved efficiency in heterogeneous catalysis To increase the range of applications, spray-dried mesoporous microparticles with other oxide composition have been achieved through simple modifications of the initial synthesis procedure.

6.5.1 Mesoporous alumina microparticles from cluster cations One approach we have developed consists in mixing directly in acidic water (at pH z 4e5) the polysaccharide nanorods and the colloidal inorganic precursors. Provided the resulting suspensions are stable, this would allow for the formation of porous oxide materials using a simple route that additionally fulfills several of the identified principles of green chemistry [131]. Following this strategy, we synthesized mesoporous alumina using positively charged a-chitin nanorods as tem4þ plates and cationic alumina precursors of different charge and nuclearity: Al(H2O)3þ 6 (Al1), Al2(OH)2(H2O)8 (Al2), 7þ 18þ ε-Al13O4(OH)24(H2O)12 (Al13) and Al30O8(OH)56(H2O)24 (Al30) [132]. The stable aqueous suspensions were spray-dried in air to yield hybrid spheroid microparticles. After calcination in air, mesoporous alumina microparticles were obtained. The texture (pore geometry and volume) greatly depended on the chitin volume fraction in the hybrids and on the nature of the alumina precursor (Fig. 6.10). Compared to small cations (Al1, Al2), the use of Al13 tridecamer and Al30 tricontamer cations lead to better defined and elongated mesopores (dpore  15 nm) owing to the effective coating of chitin nanorods by these Al oxo-hydroxo clusters that also act as pre-condensed units. This simple and fast synthesis based on the interactions between well-defined inorganic and bio-organic colloids should be extendible to other systems, and notably a variety of inorganic clusters and nanoparticles.

(A)

(B) 300

1

250

Al1

0.8

Vads. / cm3.g-1

Al2

φPOR

0.6 Al13 0.4 Al30 0.2

0 0.2

0.4

0.6

φCHI

0.8

200 150 Al1

100

Al2

50

porosity only created by chitin nanorods

0

large (>15 nm) and well-defined pores

1

0

Al13

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Al30

0.9

1

p/p0

FIG. 6.10 Variations of the textural properties of mesoporous alumina microparticles as a function of the cationic alumina precursors (see text for details). (A) Pore volume fraction fPOR as a function of initial chitin volume fraction fCHI. Dashed lines are only guide to eyes. (B) N2 sorption isotherms (77 K) of mesoporous alumina obtained at fCHI ¼ 0.65. Adapted with permission from Sachse, Chem Eur J 2015;21:3206e10.

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

99

6.5.2 Silica-titania mesoporous microparticles and applications in heterogeneous catalysis Another way to obtain mesoporous materials of varied composition is to replace part of the siloxane oligomers used in the co-assembly approach described in Sections 6.2 and 6.4 by other inorganic precursors. Simple variations in the synthesis routes might then allow to optimize the final performances of the materials. This has been demonstrated in the case of mesoporous silica-titania materials for applications in heterogeneous catalysis [133,134]. A first series of samples was obtained by mixing together in ethanol the siloxane oligomers and a Ti4þ monomer precursor (Ti(acac)2(OiPr)2) [133]. The sol was then added to a suspension of a-chitin nanorods. For molar ratios Si/ Ti  19, the final mesoporous silica-titania microparticles, obtained after spray-drying and calcining, present very similar morphology and pore textures to those of their mesoporous silica counterparts (Fig. 6.11). These mesoporous materials, in which Ti4þ cations are dispersed in the silica matrix, showed interesting catalytic performances for the mild oxidation of bulky sulfur compounds (Fig. 6.12A). In particular, the conversion of sulfur compounds into sulfones depends on the pore

FIG. 6.11 Morphology and porosity of mesoporous silica-titania microparticles (Si/Ti ¼ 19). (A and B) SEM images for fCHI ¼ 0.1 (A) and 0.65 (B). (C) Correlation between the volume fractions fCHI and fPOR. The dashed line is a guide for eyes. Adapted from Sachse, et al. Catal Sci Technol 2015;5:415e27 with permission from The Royal Society of Chemistry.

FIG. 6.12 (A) Sulfoxidation reactions carried out over the silica-titania mesoporous catalysts for methyl-phenyl sulfide (MPS, z 8 Å) and dibenzothiophene (DBT, z 11 Å) using hydrogen peroxide (50 wt% in water). (B and C) Conversion of MPS (after 50 min, B) and DBT (after 2 h, C) as a function of the pore volume fraction fPOR of the mesoporous catalysts (Si/Ti ¼ 19). The dashed lines are only guides for eyes. Adapted from Sachse, et al. Catal Sci Technol 2015;5:415e27 with permission from The Royal Society of Chemistry.

100 PART | II Biotechnology and biomedicine

Ti

+

+

Si Chin rods

Chin rods Chin rods

Chin rods

FIG. 6.13 Schematic representation of the synthesis route used to form mesoporous silica-titania microparticles with Ti sites preferentially located at the mesopore surface.

volume fraction fPOR (Fig. 6.12B and C) that depends in turn on the initial chitin volume fraction fCHI (Fig. 6.11C). Clearly, the properties of the catalysts are here related to the mesoporosity created through the co-assembly approach. The performances of the catalysts (initial rate of conversion, productivity) have been improved by modifying slightly the synthesis conditions [134]. Another series of mesoporous silica-titania microparticles was obtained by mixing first the same Ti4þ monomer precursor with an ethanolic suspension of a-chitin nanorods. The siloxane oligomers were added in a second step (Fig. 6.13). In this case, the chemical groups on the surface of the chitin crystals (hydroxyl and de-acetylated amino groups) are used to complex Ti4þ before the formation of the siloxane network so as to favor the location of Ti sites at the pore surface after removal of chitin by calcination. Therefore, in addition to the possibility of adjusting the chemical composition and using organometallic precursors of controllable reactivity, one supplementary advantage of these syntheses is the possibility to functionalize selectively the final mesopore surface.

6.6 Conclusion In this chapter, we have presented recent research on the syntheses and properties of polysaccharide-silica particles and related materials. This type of nanocomposites can be formed using hybrid suspensions of polysaccharide nanorods and nanosized inorganic precursors (oligomers, clusters) through self-assembly and sol-gel processes. The texture and the morphology of the obtained materials can be tuned by choosing specific elaboration conditions like applying external fields (electric, magnetic) or processing techniques like spray-drying. The flexibility of the described synthesis procedures allows for the modulation of the nanocomposites chemical nature and composition (e.g. cellulose vs. chitin, silica vs. alumina). This opens the way to various applications, among which the formation of efficient catalysts after removal of the biopolymers has been most studied. Interesting applicative perspectives can be envisioned for these bio-based self-assembled nanocomposites. For instance in the biomedical field, the development of new drug delivery systems where the active molecule is encapsulated in hybrid polysaccharide-oxide colloids, or electrospun tissues made of this new class of textured nanocomposites, are future lines of research with high application potential.

References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

Klein LC, editor. Sol-Gel technology for thin films, fibers, preforms, electronics, and specialty shapes. New Jersey: Noyes Publications; 1988. Brinker CJ, Scherer GW, editors. Sol-Gel Science. The physics and chemistry of Sol-Gel processing. San Diego: Academic Press; 1990. Hench LL, West JK. The sol-gel process. Chem Rev 1990;90:33e72. Dujardin E, Mann S. Bio-inspired materials chemistry. Adv Mater 2002;14:775e88. Sanchez C, Arribart H, Guille MMG. Biomimetism and bioinspiration as tools for the design of innovative materials and systems. Nature Mater 2005;4:277e88. Baccile N, et al. Introducing ecodesign in silica sol-gel materials. J Mater Chem 2009;19:8537e59. Brinker CJ, et al. Evaporation-induced self-assembly: nanostructures made easy. Adv Mater 1999;11(7):579e85. Whitesides GM, Grzybowski B. Self-assembly at all scales. Science 2002;295:2418e21. Mann S. Self-assembly and transformation of hybrid nano-objects and nanostructures under equilibrium and non-equilibrium conditions. Nature Mater 2009;8:781e92. Ozin GA, et al. Nanofabrication by self-assembly. Mater Today 2009;12(5):12e23. Ogasawara W, et al. Template mineralization of ordered macroporous chitin-silica composites using a cuttlebone-derived organic matrix. Chem Mater 2000;12(10):2835eþ.

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

101

[12] Zhang DY, Qi LM. Synthesis of mesoporous titania networks consisting of anatase nanowires by templating of bacterial cellulose membranes. Chem Commun 2005;(21):2735e7. [13] Zhang W, et al. Morphosynthesis of hierarchical ZnO replica using butterfly wing scales as templates. Microporous Mesoporous Mater 2006;92(1e3):227e33. [14] Huang JY, Wang XD, Wang ZL. Controlled replication of butterfly wings for achieving tunable photonic properties. Nano Lett 2006;6(10):2325e31. [15] Ehrlich H. Chitin and collagen as universal and alternative templates in biomineralization. Int Geol Rev 2010;52(7e8):661e99. [16] Spinde K, et al. Biomimetic silicification of fibrous chitin from diatoms. Chem Mater 2011;23(11):2973e8. [17] Wysokowski M, et al. An extreme biomimetic approach: hydrothermal synthesis of beta-chitin/ZnO nanostructured composites. J Mater Chem B 2013;1(46):6469e76. [18] Nguyen TD, MacLachlan MJ. Biomimetic chiral nematic mesoporous materials from crab cuticles. Adv Opt Mater 2014;2(11):1031e7. [19] Henry A, et al. Conversion of nanocellulose aerogel into TiO2 and TiO2@C nano-thorns by direct anhydrous mineralization with TiCl4. Evaluation of electrochemical properties in Li batteries. ACS Appl Mater Interfaces 2015;7(27):14584e92. [20] Zollfrank C, et al. Biotemplating of inorganic functional materials from polysaccharides. Bioinspired Biomimetic Nanobiomater 2012;1(1):13e25. [21] Wicklein B, Salazar-Alvarez G. Functional hybrids based on biogenic nanofibrils and inorganic nanomaterials. J Mater Chem A 2013;1(18):5469e78. [22] Kelly JA, et al. The development of chiral nematic mesoporous materials. Acc Chem Res 2014;47(4):1088e96. [23] Boury B, Plumejeau S. Metal oxides and polysaccharides: an efficient hybrid association for materials chemistry. Green Chem 2015;17(1):72e88. [24] Singh V, et al. Polysaccharide-silica hybrids: design and applications. Polym Rev 2016;56(1):113e36. [25] Belamie E, Alonso B. Hybrid nanocomposites through colloidal interactions between crystalline polysaccharide nanoparticles and oxide precursors. In: Klein L, Aparicio M, Jitianu A, editors. Handbook of sol-gel science and technology. Springer International Publishing; 2016. p. 1e39. [26] Meseck GR, Terpstra AS, MacLachlan MJ. Liquid crystal templating of nanomaterials with nature’s toolbox. Curr Opin Colloid Interface Sci 2017;29:9e20. [27] Liu QY, et al. Progress in rigid polysaccharide-based nanocomposites with therapeutic functions. J Mater Chem B 2017;5(29):5690e713. [28] Marchessault RH, Morehead FF, Walter NM. Liquid crystal systems from fibrillar polysaccharides. Nature 1959;184(4686):632e3. [29] Revol JF, et al. Helicoidal self-ordering of cellulose microfibrils in aqueous suspension. Int J Biol Macromol 1992;14(3):170e2. [30] Revol JF, Marchessault RH. In-vitro chiral nematic ordering of chitin crystallites. Int J Biol Macromol 1993;15(6):329e35. [31] Belamie E, Giraud-Guille MM. Liquid-crystalline behavior in aqueous suspensions of elongated chitin microcrystals. Trends Colloid Interface Sci XVII 2004;126:159e62. [32] Fan Y, Saito T, Isogai A. Chitin nanocrystals prepared by TEMPO-mediated oxidation of alpha-chitin. Biomacromolecules 2008;9(1):192e8. [33] Fan YM, Saito T, Isogai A. TEMPO-mediated oxidation of beta-chitin to prepare individual nanofibrils. Carbohydr Polym 2009;77(4):832e8. [34] Fan YM, et al. Comparative characterization of aqueous dispersions and cast films of different chitin nanowhiskers/nanofibers. Int J Biol Macromol 2012;50(1):69e76. [35] Zeng JB, et al. Chitin whiskers: an overview. Biomacromolecules 2012;13(1):1e11. [36] Ifuku S, et al. Preparation of chitin nanofibers with a uniform width as alpha-chitin from crab shells. Biomacromolecules 2009;10(6):1584e8. [37] Mushi NE, et al. Nanostructured membranes based on native chitin nanofibers prepared by mild process. Carbohydr Polym 2014;112:255e63. [38] Das P, et al. Tough and catalytically active hybrid biofibers wet-spun from nanochitin hydrogels. Biomacromolecules 2012;13(12):4205e12. [39] Habibi Y, Lucia LA, Rojas OJ. Cellulose nanocrystals: chemistry, self-assembly, and applications. Chem Rev 2010;110(6):3479e500. [40] Mukherjee SM, Woods HJ. X-ray and electron microscope studies of the degradation of cellulose by sulphuric acid. Biochim Biophys Acta 1953;10(4):499e511. [41] Marchessault R, Morehead FF, Koch MJ. Some hydrodynamic properties of neutral suspensions of cellulose crystallites as related to size and shape. J Colloid Sci 1961;16(4):327e&. [42] Dong XM, Revol JF, Gray DG. Effect of microcrystallite preparation conditions on the formation of colloid crystals of cellulose. Cellulose 1998;5(1):19e32. [43] Elazzouzi-Hafraoui S, et al. The shape and size distribution of crystalline nanoparticles prepared by acid hydrolysis of native cellulose. Biomacromolecules 2008;9(1):57e65. [44] Revol JF. On the cross-sectional shape of cellulose crystallites in Valonia ventricosa. Carbohydr Polym 1982;2:123e34. [45] Sugiyama J, et al. Lattice images from ultrathin sections of cellulose microfibrils in the cell-wall of Valonia-macrophysa Kutz. Planta 1985;166(2):161e8. [46] Hanley SJ, et al. Atomic force microscopy and transmission electron microscopy of cellulose from Micrasterias denticulata; evidence for a chiral helical microfibril twist. Cellulose 1997;4(3):209e20. [47] Kim NH, et al. The cellulose system in the cell wall of Micrasterias. J Struct Biol 1996;117(3):195e203. [48] Onsager L. The effects of shapes on the interaction of colloidal particles. Ann N Y Acad Sci 1949;51:627e59. [49] Stroobants A, Lekkerkerker HNW, Odijk T. Effect of electrostatic interaction on the liquid crystal phase transition in solutions of rodlike polyelectrolytes. Macromolecules 1986;19(8):2232e8. [50] Vroege GJ, Lekkerkerker HNW. Phase transitions in lyotropic colloidal and polymer liquid crystals. Rep Prog Phys 1992;55(8):1241e309. [51] Belamie E, et al. Possible transient liquid crystal phase during the laying out of connective tissues: alpha-chitin and collagen as models. J Phys Condens Matter 2006;18(13):115e29.

102 PART | II Biotechnology and biomedicine

[52] Bouligand Y. Sur une architecture torsadée répandue dans de nombreuses cuticules d’Arthropodes. Comptes rendus hebdomadaires des séances de l’Académie des sciences 1965;261:3665e8. [53] Bouligand Y. Liquid crystals and biological morphogenesis: ancient and new questions. Comptes Rendus Chimie 2008;11(3):281e96. [54] Hamley IW. Liquid crystal phase formation by biopolymers. Soft Matter 2010;6(9):1863e71. [55] Neville AC. Insect ultrastructure. Oxford: Blackwell Scientific Publications; 1970. [56] Roland JC, Reis D, Vian B. Liquid crystal order and turbulence in the planar twist of the growing plant cell walls. Tissue Cell 1992;24(3):335e45. [57] Caveney S. Cuticle reflectivity and optical activity in scarab beetles: role of uric acid. Proc R Soc Ser B 1971;178(1051):205e25. [58] Hébant CW, Lee DW. Ultrastructural basis and developmental control of blue iridescence in salginella leaves. Am J Botany 1984;71:216e9. [59] Lee DW. Iridescent blue plants. Am Sci 1997;85(1):56e63. [60] Raabe D, Sachs C, Romano P. The crustacean exoskeleton as an example of a structurally and mechanically graded biological nanocomposite material. Acta Mater 2005;53(15):4281e92. [61] Chen PY, et al. Structure and mechanical properties of crab exoskeletons. Acta Biomater 2008;4(3):587e96. [62] Ehrlich H, et al. Nanostructural organization of naturally occurring composites - Part I: silica-collagen-based biocomposites. J Nanomater 2008:1e8. https://doi.org/10.1155/2008/623838. ID 623838. [63] Fowler CE, et al. Tobacco mosaic virus liquid crystals as templates for the interior design of silica mesophases and nanoparticles. Adv Mater 2001;13(16):1266e9. [64] Dujardin E, Blaseby M, Mann S. Synthesis of mesoporous silica by sol-gel mineralisation of cellulose nanorod nematic suspensions. J Mater Chem 2003;13(4):696e9. [65] Shopsowitz KE, Hamad WY, MacLachlan MJ. Flexible and iridescent chiral nematic mesoporous organosilica films. J Am Chem Soc 2012;134(2):867e70. [66] Nguyen TD, Hamad WY, MacLachlan MJ. Tuning the iridescence of chiral nematic cellulose nanocrystals and mesoporous silica films by substrate variation. Chem Commun 2013;49(96):11296e8. [67] Tran A, Hamad WY, MacLachlan MJ. Tactoid annealing improves order in self-assembled cellulose nanocrystal films with chiral nematic structures. Langmuir 2018;34(2):646e52. [68] Kelly JA, et al. Chiral nematic stained glass: controlling the optical properties of nanocrystalline cellulose-templated materials. Langmuir 2012;28(50):17256e62. [69] Schlesinger M, et al. Chiral nematic cellulose-gold nanoparticle composites from mesoporous photonic cellulose. Chem Commun 2015;51(3):530e3. [70] Schlesinger M, Hamad WY, MacLachlan MJ. Optically tunable chiral nematic mesoporous cellulose films. Soft Matter 2015;11(23):4686e94. [71] Alonso B, Belamie E. Chitin-silica nanocomposites by self-assembly. Angew Chem Int Ed 2010;49(44):8201e4. [72] Belamie E, et al. Tunable hierarchical porosity from self-assembled chitin-silica nano-composites. J Mater Chem 2011;21(42):16997e7006. [73] Shopsowitz KE, et al. Free-standing mesoporous silica films with tunable chiral nematic structures. Nature 2010;468(7322):422. U246. [74] Shopsowitz KE, et al. Biopolymer templated glass with a twist: controlling the chirality, porosity, and photonic properties of silica with cellulose nanocrystals. Adv Funct Mater 2014;24(3):327e38. [75] Scheel H, Zollfrank C, Greil P. Luminescent silica nanotubes and nanowires: preparation from cellulose whisker templates and investigation of irradiation-induced luminescence. J Mater Res 2009;24(5):1709e15. [76] Gruber S, et al. Cellulose-biotemplated silica nanowires coated with a dense gold nanoparticle layer. Mater Chem Phys 2011;129(1e2):19e22. [77] Buskens P, et al. Highly porous, ultra-low refractive index coatings produced through random packing of silicated cellulose nanocrystals. Colloids Surf A Physicochem Eng Aspects 2015;487:1e8. [78] Chen L, Berry RM, Tam KC. Synthesis of beta-cyclodextrin-modified cellulose nanocrystals (CNCs)@Fe3O4@SiO2 superparamagnetic nanorods. ACS Sustain Chem Eng 2014;2(4):951e8. [79] Smolyakov G, et al. AFM PeakForce QNM mode: evidencing nanometre-scale mechanical properties of chitin-silica hybrid nanocomposites. Carbohydr Polym 2016;151:373e80. [80] Smolyakov G, et al. PeakForce QNM AFM study of chitin-silica hybrid films. Carbohydr Polym 2017;166:139e45. [81] Cardoso L, et al. Synthesis of textured polysaccharideesilica nanocomposites: a comparison between cellulose and chitin nanorod precursors. New J Chem 2017;41:6014e24. [82] Vachoud L, et al. Rheological study of chitin nanorods - siloxane oligomers suspensions in ethanol. Colloids Surf. A 2018;558:470e8. [83] Lekkerkerker HNW, et al. On the isotropic-liquid crystal phase separation in a solution of rodlike particles of different lengths. J Chem Phys 1984;80(7):3427e33. [84] Samir MASA, et al. Preparation of cellulose whiskers reinforced nanocomposites from an organic medium suspension. Macromolecules 2004;37(4):1386e93. [85] Nelson K, Deng YL. The shape dependence of core-shell and hollow titania nanoparticles on coating thickness during layer-by-layer and sol-gel synthesis. Nanotechnology 2006;17(13):3219e25. [86] Azzam F, et al. Preparation by grafting onto, characterization, and properties of thermally responsive polymer-decorated cellulose nanocrystals. Biomacromolecules 2010;11(12):3652e9. [87] Okura H, Wada M, Serizawa T. Dispersibility of HCl-treated cellulose nanocrystals with water-dispersible properties in organic solvents. Chem Lett 2014;43(5):601e3.

From nano-to micro-particles of polysaccharide-silica composites through self-assembly Chapter | 6

103

[88] Bruckner JR, et al. Enhancing self-assembly in cellulose nanocrystal suspensions using high-permittivity solvents. Langmuir 2016;32(38):9854e62. [89] Orts WJ, et al. Enhanced ordering of liquid crystalline suspensions of cellulose microfibrils: a small-angle neutron scattering study. Macromolecules 1998;31(17):5717e25. [90] Ebeling T, et al. Shear-induced orientation phenomena in suspensions of cellulose microcrystals, revealed by small angle X-ray scattering. Langmuir 1999;15(19):6123e6. [91] Bordel D, Putaux J-L, Heux L. Orientation of native cellulose in an electric field. Langmuir 2006;22(11):4899e901. [92] Habibi Y, Chanzy H, Vignon MR. TEMPO-mediated surface oxidation of cellulose whiskers. Cellulose 2006;13(6):679e87. [93] Boltoeva MY, et al. Electric-field alignment of chitin nanorod-siloxane oligomer reactive suspensions. Langmuir 2013;29(26):8208e12. [94] Metselaar L, et al. Electric-field-induced shape transition of nematic tactoids. Phys Rev E 2017;96(2). [95] Sugiyama J, Chanzy H, Maret G. Orientation of cellulose microcrystals by strong magnetic-fields. Macromolecules 1992;25(16):4232e4. [96] Revol JF, et al. Chiral nematic suspensions of cellulose crystallites - phase-separation and magnetic-field orientation. Liq Cryst 1994;16(1): 127e34. [97] Dong XM, Gray DG. Induced circular dichroism of isotropic and magnetically-oriented chiral nematic suspensions of cellulose crystallites. Langmuir 1997;13(11):3029e34. [98] Kimura F, et al. Magnetic alignment of the chiral nematic phase of a cellulose microfibril suspension. Langmuir 2005;21(5):2034e7. [99] De France KJ, et al. Cooperative ordering and kinetics of cellulose nanocrystal alignment in a magnetic field. Langmuir 2016;32(30):7564e71. [100] Kresge CT, et al. Ordered mesoporous molecular sieves synthesized by a liquid-crystal template mechanism. Nature 1992;359:710e2. [101] Corma A. From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem Rev 1997;97:2373e419. [102] Ciesla U, Schüth F. Ordered mesoporous materials. Microporous Mesoporous Mater 1999;27:131e49. [103] Stein A, Melde BJ, Schroden RC. Hybrid inorganic-organic mesoporous silicates. Nanoscopic reactors coming of age. Adv Mater 2000;12(19):1403e19. [104] Sayari A, Hamoudi S. Periodic mesoporous silica-based organic-inorganic nanocomposite materials. Chem Mater 2001;13:3151e68. [105] Vallet-Regi M. Ordered mesoporous materials in the context of drug delivery systems and bone tissue engineering. Chem Eur J 2006;12:5934e43. [106] van Bommel KJC, Friggeri A, Shinkai S. Organic templates for the generation of inorganic materials. Angew Chem Int Ed 2003;42(9):980e99. [107] Sotiropoulou S, et al. Biotemplated nanostructured materials. Chem Mater 2008;20:821e34. [108] Zhou H, Fan TX, Zhang D. Biotemplated materials for sustainable energy and environment: current status and challenges. ChemSusChem 2011;4(10):1344e87. [109] Fernandes FM, Coradin T, Aime C. Self-assembly in biosilicification and biotemplated silica materials. Nanomaterials 2014;4(3):792e812. [110] Masters K. Spray-drying in practice. Charlottenlund: SprayDryConsult International; 2002. [111] Okuyama K, et al. Preparation of functional nanostructured particles by spray drying-A review. Adv Powder Technol 2006;17:587e611. [112] Boissiere C, et al. Aerosol route to functional nanostructured inorganic and hybrid porous materials. Adv Mater 2011;23:599e623. [113] Bruinsma PJ, et al. Mesoporous silica synthesized by solvent evaporation: spun fibers and spray-dried hollow spheres. Chem Mater 1997;9:2507e12. [114] Lu Y, et al. Aerosol-assisted self-assembly of mesostructured spherical nanoparticles. Nature 1999;398(6724):223e6. [115] Baccile N, Grosso D, Sanchez C. Aerosol generated silica particles. J Mater Chem 2003;13:3011e6. [116] Boissière C, et al. First in-situ SAXS studies of the mesostructuration of spherical silica and titania particles during spray-drying process. Chem Commun 2003:2798e9. [117] Alonso B, et al. Morphological and textural control of spray-dried mesoporous silica-based spheres. J Mater Chem 2004;14:2006e16. [118] Alonso B, et al. New insights into the formation of textures through spray-drying and self-assembly. Microporous Mesoporous Mater 2007;106(1e3):76e94. [119] Boissière C, et al. Nanocrystalline mesoporous gamma-alumina powders “UPMC1 materials” gathers thermal and chemical stability with high surface area. Chem Mater 2006;18:5238e43. [120] Tsung CK, et al. A general route to diverse mesoporous metal oxide submicrospheres with highly crystalline frameworks. Angew Chem Int Ed 2008;47(45):8682e6. [121] Pega S, et al. Direct aerosol synthesis of large-pore amorphous mesostructured aluminosilicates with superior acid-catalytic properties. Angew Chem Int Ed 2009;48:2748e87. [122] Debecker DP, et al. One-pot aerosol route to MoO3-SiO2-Al2O3 catalysts with ordered super microporosity and high Olefin metathesis activity. Angew Chem Int Ed 2012;51(9):2129e31. [123] Lu Y, et al. Evaporation-induced self-assembly of hybrid bridged silsesquioxane film and particulate mesophases with integral organic functionality. J Am Chem Soc 2000;122:5258e61. [124] Alonso B, et al. New routes to mesoporous silica-based spheres with functionalised surfaces. Chem Commun 2005:1746e8. [125] Melnyk IV, et al. Spray-dried mesoporous silica microspheres with adjustable textures and pore surfaces homogenously covered by accessible thiol functions. J Mater Chem 2008;18(12):1368e82. [126] Melnyk IV, et al. Spray-dried porous silica microspheres functionalised by phosphonic acid groups. Microporous Mesoporous Mater 2012;152:172e7. [127] Hampsey JE, et al. One-step synthesis of mesoporous metal-SiO2 particles by an aerosol-assisted self-assembly process. Chem Mater 2005;17(9):2475e80.

104 PART | II Biotechnology and biomedicine

[128] Julián-López B, et al. Mesoporous maghemite-organosilica microspheres: a promising route towards multifunctional platforms for smart diagnosis and therapy. J Mater Chem 2007;17:1563e9. [129] Ruiz-Hernández E, et al. Aerosol-Assisted synthesis of magnetic mesoporous silica spheres for drug targeting. Chem Mater 2007;19:3455e63. [130] Fatnassi M, et al. Tuning nanophase separation and drug delivery kinetics through spray-drying and self-assembly. New J Chem 2010;34:607e10. [131] Anastas P, Eghbali N. Green chemistry: principles and practice. Chem Soc Rev 2010;39:301e12. [132] Sachse A, et al. Mesoporous alumina from colloidal biotemplating of Al clusters. Chem A Eur J 2015;21(8):3206e10. [133] Sachse A, et al. Efficient mesoporous silica-titania catalysts from colloidal self-assembly. Chem Commun 2012;48(86):10648e50. [134] Sachse A, et al. Improved silica-titania catalysts by chitin biotemplating. Catal Sci Technol 2015;5(1):415e27.