Colloidal-electrochemical fabrication strategies for functional composites of linear polyethylenimine

Journal of Colloid and Interface Science 552 (2019) 1–8

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Regular Article

Colloidal-electrochemical fabrication strategies for functional composites of linear polyethylenimine Z.Z. Wang a, A. Clifford a, J. Milne a, R. Mathews b, I. Zhitomirsky a,⇑ a b

Department of Materials Science and Engineering, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4L7, Canada Advanced Ceramics Corporation, 2536 Bristol Circle, Oakville, ON L6H 5S1, Canada

g r a p h i c a l a b s t r a c t

a r t i c l e

i n f o

Article history: Received 13 March 2019 Revised 9 May 2019 Accepted 11 May 2019 Available online 11 May 2019 Keywords: Polyethylenimine Electrodeposition Hemoglobin Cyclodextrin Oxide Hydroxide

a b s t r a c t Colloidal-electrochemical fabrication strategies have been developed for the deposition of linear polyethylenimine (LPEI) composite materials. Electrophoretic deposition (EPD) allowed for the fabrication of composite films containing Mn3O4 and ZnO nanoparticles, as well as advanced flame retardant materials, such as halloysite nanotubes and memory-type Al-Mg-Zr complex hydroxide (AMZ) in the matrix of the water-insoluble LPEI. A liquid-liquid extraction method has been designed for the agglomerate-free processing of AMZ particles. Efficient extraction was achieved using decylphosphonic acid as an extractor. A conceptually new polymer complex (PC)-EPD method has been developed, which is based on the use of LPEI-metal ion complexes. Proof-of-concept studies involved the fabrication of LPEI-Ni(OH)2 and LPEI-MnOx nanocomposites. The composites showed valuable flame retardant and charge-storage properties. The analysis of basic EPD and PC-EPD mechanisms as well as complexing properties of LPEI has driven the development of new strategies for the fabrication of organic composites. Hemoglobin was used as a model protein for the fabrication of composite films. Another important finding was the fabrication of composites, containing cyclodextrin, which is a unique carrier of various functional organic molecules. EPD and PC-EPD are versatile methods, which allow for the deposition of novel LPEI based composites containing various functional materials. Ó 2019 Elsevier Inc. All rights reserved.

1. Introduction

⇑ Corresponding author. E-mail address: [email protected] (I. Zhitomirsky). https://doi.org/10.1016/j.jcis.2019.05.039 0021-9797/Ó 2019 Elsevier Inc. All rights reserved.

Polyethylenimine (PEI) polymers are broadly used for a variety of applications, including material synthesis, colloidal processing, particle dispersion and surface modification [1–4]. The aqueous solubility of PEI polymers is dependent on the polymer structure.

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Branched polyethylenimines (BPEIs) are water-soluble and exist in liquid form, whereas linear polyethylenimines (LPEIs) exist as solids and are water-insoluble [5]. LPEIs contain secondary amino groups, while BPEIs have primary, secondary and tertiary amines. The amino groups of BPEIs and LPEIs can be protonated in acidic solutions and the protonated polymers exhibit properties of cationic polyelectrolytes in aqueous solutions at low pH values [5]. The cationic properties of BPEIs have been utilized for electrophoretic deposition (EPD) of materials [6,7]. It has also been found that BPEIs exhibit strong adsorption on inorganic surfaces, which is beneficial for particle dispersion and surface modification [7,8]. Although BPEIs have attracted significant interest, their thin film applications are limited due to their high solubility in water. Another difficulty is related to protonation of BPEI molecules [9]. The pH of aqueous BPEI solutions is typically about 11 and at this pH the BPEI molecules are electrically neutral. The protonation of BPEIs requires significant amounts of acid, which contaminate solutions as well as dispersions of colloidal particles, containing BPEIs [9]. In contrast, LPEIs can easily be protonated. The deprotonated LPEIs are used for thin film applications, due to their insolubility in water, film-forming and binding properties [10,11]. The electrokinetic and chemical properties of the LPEI macromolecules can be modified by the formation of LPEI-metal ion complexes [12]. BPEIs and LPEIs are attractive materials for biomedical applications, such as biosensors, biomedical implants, drug and gene delivery [13]. Many applications are based on the remarkable ability of LPEIs to form complexes with various inorganic and organic materials. LPEIs are increasingly being explored as gene carriers [14]. Many investigations focused on the analysis of LPEI-DNA complex formation [15–17]. In contrast to other polyelectrolytes, LPEI offers benefits of stronger transfection efficiencies and improved protection of DNA [16]. It was found that LPEIs have enhanced gene expression and lower toxicity, compared to BPEIs [15]. Enhanced biocompatibility was achieved [18] in LPEI-DNAmetal ion complexes. In addition, LPEI-cyclodextrin (CD) complexes have been developed for drug delivery [19]. Enhanced complex formation was observed [19] at high pH above pKa (8.9) of LPEI. Many applications of LPEI are based on the use of thin films [20–23]. In a previous investigation [24] we found that LPEI films can be deposited by EPD. The solutions for EPD were prepared by protonation and dissolution of LPEI:

LPEI + Hþ ! LPEI  Hþ

ð1Þ

The mechanism of deposition was based on local pH increase at the cathode surface due to the electrochemical reaction:

2H2 O + 2e ! H2 + 2OH

ð2Þ +

The cataphoresis of LPEI-H and charge neutralization led to the formation of insoluble cathodic LPEI films [24]:

LPEI  Hþ + OH ! LPEI + H2 O

ð3Þ

In our previous investigation [24] we focused on the analysis of deposition yield at different LPEI concentrations. It was found that LPEI films fabricated using EPD can be used for corrosion protection of metals. Moreover, EPD was used for the fabrication of composite films, containing MnO2, TiO2 and hydrotalcite particles in the LPEI matrix [24]. Building upon advances reported in our previous work, novel nanocomposites and advanced functional materials may be developed using LPEI. The key advantage of LPEI, compared to other cationic polyelectrolytes, such as chitosan and poly-lysine, is the high charge density of LPEI [16]. Of particular interest are complexes of LPEIs with metal ions and organic mole-

cules, which can potentially be used for the development of new composites as well as colloidal and electrochemical techniques for their deposition. The goal of this investigation was to develop new combined colloidal-electrochemical strategies for the fabrication of composite materials containing LPEI. Experimental results presented below demonstrate that LPEI can be used as charging, dispersing and film-forming agent for the co-EPD of LPEI with Mn3O4, ZnO, halloysite nanotubes and Al-Mg-Zr complex hydroxide material (AMZ), which exhibits unique memory-type flame retardant properties. In this investigation, particle extraction through liquid-liquid interface (PELLI) has been utilized for the formation of stable suspensions for EPD. Reduced agglomeration of AMZ, prepared by chemical precipitation, was achieved by the PELLI method using decylphosphonic acid (DPA) as an extractor. Polymer-metal ion complex (PC)-EPD method has been developed for the fabrication of nanocomposites. The method was based on the use of LPEImetal ion complexes for EPD and the electrosynthesis of metal oxides and hydroxides in the LPEI matrix. It was found that PC-EPD can be used for the fabrication of electrodes for energy storage devices. Another new finding of this study was the possibility of deposition of LPEI composites, containing functional organic molecules, such as hemoglobin (Hb) and CD. The composite materials have potential applications in biosensors and drug delivery. The deposition mechanisms and applications of obtained materials were discussed. Our new deposition strategies pave the way for the colloidalelectrochemical processing of new functional materials.

2. Experimental procedures Halloysite nanotubes (diameter 30–70 nm, length 1–3 lm), ZnO (70–100 nm), decylphosphonic acid (DPA), Al(NO3)39H2O, Mg (NO3)26H2O, ZrOCl28H2O, hemoglobin (Hb), a-cyclodextrin (CD), NiCl26H2O and MnCl24H2O (Aldrich), LPEI (Polysciences) were used. Mn3O4 nanoparticles (size 50–100 nm) were synthesized according to the procedure described in Ref. [25]. AMZ was produced by co-precipitation from mixed Al(NO3)3, Mg(NO3)2 and ZrOCl2 solutions at pH = 10. Al:Mg:Zr atomic ratio was 0.78:3:0.14. The as-precipitated AMZ particles (size 30–50 nm) were extracted to the 1-butanol phase using DPA as an extractor. The mass ratio of AMZ:DPA was 4:1. The electrochemical cell for cathodic deposition contained a stainless steel cathode and Pt anode. The distance between the electrodes was 17 mm. EPD was performed at constant voltages of 20–50 V. Polymer-mediated electrosynthesis was performed at constant current densities of 1–5 mA cm2. Colloidal-electrodeposition strategies involved EPD or PC-EPD. 1 g of LPEI was protonated and dissolved in 100 mL water using 1 mL of acetic acid to form LPEI-H+ solutions for EPD. The suspensions for EPD of LPEI-Mn3O4, LPEI-ZnO, LPEI-halloysite, and LPEIAMZ contained 1 g L1 LPEI-H+ and 0.5–2 g L1 of the inorganic components in a mixed water–ethanol (20% water) or waterethanol-1-butanol (20% water, 20% 1-butanol) solvents. Alcohol solvents were used to reduce gas evolution at the electrode surface during deposition. However, water is necessary for OH generation (Eq. (2)), and thus mixed solvents were used to combine the advantageous properties of alcohol and water. In the PC-EPD method, 0.5 g LPEI was dissolved in 100 mL of aqueous solutions, which contained either 1.19 g NiCl26H2O or 0.99 g MnCl24H2O to form LPEI-Ni2+ or LPEI-Mn2+ solutions. The solutions for PC-EPD contained 0.5 g L1 LPEI and 5 mM NiCl2 or MnCl2 in water-ethanol (20% water) solvent. EPD of LPEI-Hb was performed from aqueous solutions, containing 1 g L1 LPEI and 1 g L1 Hb. Co-deposition of LPEI and CD was

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performed from solutions, containing 1 g L1 LPEI, 1 g L1 CD and 5 mM MnCl2 in a water-ethanol (20% water) solvent. Equipment for XRD, TGA, DTA, FTIR, and SEM studies has been described in previous investigations [26,27]. Cyclic voltammetry (CV) studies were performed using a potentiostat (PARSTAT model 2273, Ametek, USA). A three-electrode cell contained a working electrode (area 1 cm2), a saturated calomel electrode (SCE) and a Pt counter electrode. An aqueous 0.5 M Na2SO4 solution was used as an electrolyte. Cyclic voltammetry (CV) studies at scan rates of 2–100 mV s1 were used to calculate the integral capacitances CS = Q/DVS and Cm = Q/DVm, where Q, DV, S and m are charge, potential window, electrode area and active mass, respectively. A Bruker Bioscope Catalyst combined with a SCANASYST-AIR probe tip was used for atomic force microscopy (AFM) to characterize the surface roughness of the coating. The average surface roughness was calculated from the average roughness of a 50 lm by 50 lm area. 3. Results and discussion Fig. 1 shows an AFM image of a LPEI film deposited from 1 g L1 LPEI-H+ solution at a deposition voltage of 10 V. The maximum roughness was on the nanometer scale and the average roughness over the area measured was found to be 1.5 nm. The composition of the electrodeposition bath has been modified for the deposition of composites. Fig. 2 shows schematics of colloidal-electrodeposition mechanisms used in this investigation for the deposition of organicinorganic composites. Protonated LPEI-H+ was used for EPD of inorganic particles. In this method, LPEI-H+ adsorbed on the inorganic particles and acted as a charging and dispersing agent. Deposition process involved cataphoresis of charged particles, containing adsorbed LPEI-H+ (Fig. 2a). The LPEI-H+ discharge and deposit formation were governed by reactions (2, 3). In the PC-EPD method, LPEI was dissolved in metal (M) salt solutions to form LPEI-Mz+ complexes. It is known that PEIs exhibit the remarkable ability to form complexes with metal ions [28] and such complexes show properties of polyelectrolytes in solutions [9]. The PC-EPD mechanism (Fig. 2b) was based on cataphoresis of LPEI-Mz+, cathodic electrosynthesis of metal oxide (Eq.4) or hydroxide (Eq.5) particles, charge neutralization and film formation at the cathode surface:

LPEI  Mzþ + zOH ! LPEI + MOz=2 + (z/2)H2 O

ð4Þ

LPEI  Mzþ + zOH ! LPEI + M(OH)z

ð5Þ

PC-EPD resulted in electrosynthesis of metal oxide or hydroxide nanoparticles in LPEI matrix. This is in contrast to metal oxide or hydroxide synthesis using chemical precipitation, which requires

Fig. 1. AFM image of a LPEI film, deposited from 1 g L1 LPEI-H+ solution at a deposition voltage of 10 V.

Fig. 2. Mechanisms of electrodeposition of organic-inorganic composites: (a) EPD, involving electrophoresis of particles, containing adsorbed LPEI-H+ and charge neutralization of LPEI at the electrode surface, (b) PC-EPD, involving electrophoresis of LPEI-metal ion complexes, particle synthesis and charge neutralization of LPEI in electrode reactions.

the use of alkali for pH adjustment, whereas the PC-EPD method involved electrogenerated OH species for the synthesis of inorganic particles. PC-EPD is conceptually different from previously described electrosynthesis-EPD method, which is based on the use of strong polyelectrolytes, such as poly(diallyldimethylammonium chloride) (PDDA) with pH-independent charge [29,30]. Electrosynthesis-EPD is limited to the synthesis of oxides and hydroxides with relatively low isoelectric points. It involves independent electromigration of metal ions and polyelectrolytes, electrosynthesis and electrostatic heterocoagulation of the inorganic and organic components at the electrode surface. The PC-EPD method is different from the polymer-mediated electrosynthesis, based on the use of BPEIs, which are soluble in water and do not form films by EPD in aqueous solutions [9]. The development of the PC-EPD method was inspired by interesting electrosynthesis phenomena, such as influence of polymers on crystallinity, functional properties and size of particles, which were observed in previous electrosynthesis-EPD experiments involving the use of PDDA [30,31]. Moreover, it was found that weak polyelectrolytes, containing amino groups facilitate room temperature crystallization of functional inorganic materials in the polymer microcapsules [32,33]. The electrosynthesis-EPD method showed that polymers with amino groups can promote room temperature crystallization of particles synthesized in the polymer matrix [34]. Therefore, LPEI is a promising material for the development of the PC-EPD method. Different functional materials, such as Mn3O4, ZnO, halloysite and AMZ were used for EPD. The as-prepared AMZ particles showed significant agglomeration during the drying procedure and re-dispersion of AMZ in the EPD bath presented difficulties. The agglomeration resulted from the formation of the oxobridges due the condensation reactions of surface OH groups and energetically favorable reduction of the surface area. Therefore, PELLI was used for the direct transfer of AMZ particles, synthesized in water to 1-butanol. The selection of DPA as an extractor was based on the literature data [35] of the remarkable adsorption of phosphonic acid terminated molecules on the surface of MgAl

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double hydroxides in aqueous suspensions. We found that waterinsoluble DPA was adsorbed on the AMZ particles at the liquidliquid interface and allowed for an efficient extraction. DPA adsorption can be based on different bi-dentate or tri-dentate mechanisms, such as bridging or chelating bonding of phosphonic acid anchoring groups [36]. The DPA adsorption was confirmed by the results of FTIR studies (Fig. 3). The FTIR spectra of powder samples containing extracted AMZ showed absorptions at 2848, 2918 and 2956 cm1, which were attributed to asymmetric and symmetric vibrations of CH2 groups. Such adsorptions were not observed in the spectrum of pure AMZ. However, the FTIR spectrum of as-received DPA powder showed similar absorptions. Previous investigations showed that EPD of pure LPEI resulted in the formation of dense films. In this work, it was found that the addition of oxide particles to the LPEI-H+ solution resulted in

Fig. 3. FTIR spectra for (a) DPA and (b) AMZ extracted using DPA.

changes of film microstructure. The increase in the particle concentration in suspension resulted in increasing particle concentration in films. Fig. 4 shows SEM images of composite films, prepared by EPD from 1 g L1 LPEI-H+ solutions, containing 2 g L1 of Mn3O4, ZnO, halloysite nanotubes and AMZ. The SEM images show porous films, containing oxide or hydroxide particles. The observed porosity is mainly attributed to particle packing. Some larger pores can result from H2 evolution in electrode reaction (2). Mn3O4 and ZnO are advanced materials for energy storage, sensor and electronic applications [34,37]. Halloysite is a promising material for drug delivery, corrosion protection and flameretardant applications [26,38]. AMZ is an advanced memory-type [39] flame-retardant material. In contrast to other hydroxide materials, the thermally dehydrated AMZ shows unique ability to reconstruct its original composition, crystalline structure and flameretardant properties by adsorption of water. The flame-retardant properties of halloysite and AMZ are attributed to endothermic process of dehydration. The thermal decomposition of halloysite and AMZ resulted in mass loss of 18 and 45%, respectively, which was related to dehydration (Figs. 5, 6). The composite materials showed additional mass loss, related to burning out LPEI. The films, prepared from 1 g L1 LPEI-H+ solutions, which contained 2 g L1 of halloysite nanotubes and AMZ showed a mass loss of 48 and 63%, respectively. The ability of LPEI to form complexes with metal ions allowed for the development of PC-EPD method, which represents another promising avenue for the fabrication of composites. Experiments conducted to prove our concept were focused on the fabrication of nanocomposites using LPEI-Ni2+ and LPEI-Mn2+ complexes in solutions. Fig. 7 shows SEM images of the films prepared using this method. The films were relatively dense and uniform. However, very small pores were observed in the films prepared from LPEIMn2+ solutions. Such pores can result form H2 evolution during electrodeposition. The method resulted in the development of crack-free films. The deposition yield of the films, prepared by the PC-EPD method was lower, than that of the films prepared by EPD. It is important to note that PC-EPD involves synthesis of

Fig. 4. SEM images of composite films, prepared from 1 g L1 LPEI-H+ solutions, containing 2 g L1 (A) Mn3O4, (B) ZnO, (C) halloysite and (D) AMZ.

Z.Z. Wang et al. / Journal of Colloid and Interface Science 552 (2019) 1–8

Fig. 5. TGA data for (a) as-received halloysite and (b) a deposit, prepared from 1 g L1 LPEI-H+ solution, containing 2 g L1 halloysite.

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diffraction data can result from very small particle size and fully or partially amorphous nature of the inorganic phases (see Fig. 8). It is known that the size of the particles in the films, prepared by electrosynthesis from pure metal salt solutions is typically lower than the size of the particles in the films deposited by EPD from colloidal suspensions [40]. The polymer matrix can potentially limit the size of the electrosynthesized particles [34]. Metal oxide or hydroxide films, prepared by electrosynthesis or other wet chemical methods usually exhibit cracks attributed to drying shrinkage, especially for the films with thickness above 0.1 mm [30]. In the present work, LPEI acted as a binder, preventing cracks in the films formed by the PC-EPD method. The formation of organic-inorganic composites by PC-EPD was confirmed by TGA studies (Fig. 9). The deposits showed mass loss attributed to burning out of LPEI and dehydration. The deposit, prepared from LPEINi2+ solutions showed several steps in mass loss with a total mass loss of about 59% at 1000 sC. Therefore, the Ni(OH)2 content in the composite was 51%. Ni(OH)2 is an important charge storage material for applications in batteries. The deposit, prepared from LPEI-Mn2+ solutions showed mass loss of about 40% at 500 sC. The sample mass remained nearly constant in the range of 500–920 sC and corresponded to MnOx phase. At temperatures 920–940 sC an additional step in the mass loss was observed. A similar step [41] in the mass loss was reported in other investigations and attributed to transformation of Mn2O3 or MnOx phase to Mn3O4. The formation of the MnOx phase within the LPEI matrix was further confirmed by the results of cyclic voltammetry in 0.5 Na2SO4 solutions. The films showed a capacitive behavior in a voltage window of 0–0.9 V versus SCE, as indicated by their CV box shapes (Fig. 10a). The composite film with

Fig. 6. TGA data for (a) as-prepared AMZ and (b) a deposit, prepared from 1 g L1 LPEI-H+ solution, containing 2 g L1 AMZ.

inorganic particles. The growth of the insulating and relatively dense films can limit charge transfer, resulting in lower deposition yield. X-ray diffraction studies (CuKa and CoKa radiations) did not show diffraction peaks for deposits prepared using LPEI-Mn2+ solutions. In contrast, the deposits prepared using LPEI-Ni2+ solutions displayed broad peaks corresponding to Ni(OH)2. Such X-ray

Fig. 8. X-ray diffraction patterns (CoKa radiation) of deposits, prepared from (a) 5 mM MnCl2 and (b) 5 mM NiCl2 solutions, containing 0.5 g L1 LPEI.

Fig. 7. SEM images of deposits, prepared from (a) 5 mM MnCl2 and (b) 5 mM NiCl2 solutions, containing 0.5 g L1 LPEI.

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reversal of the Hb molecules. The negative charge of the Hb molecules prevented Hb deposition at the cathode. However, in the pH gradient range [40] at the electrode surface, the electrostatic interactions of the negatively charged Hb with the positively charged LPEI and deposition of LPEI promoted the incorporation of Hb into the composite films. Electrically neutral CD molecules were codeposited with LPEI using PC-EPD. It is suggested that the LPEICD complexation to form polypseudorotaxane [19] can facilitate the CD incorporation into the LPEI deposit. The polypseudorotaxane [19] formation is a pH-dependent process, it can be enhanced in the high pH region at the cathode surface. Fig. 11 compares the FTIR spectra of LPEI, CD and Hb with spectra of the LPEI-Hb and LPEI-CD composite films. The FTIR spectrum

Fig. 9. TGA data for deposits, prepared from (a) 5 mM MnCl2 and (b) 5 mM NiCl2 solutions, containing 0.5 g L1 LPEI.

mass of 0.12 mg cm2 showed a capacitance of 32 mF cm2 (267 F g1) at a sweep rate of 2 mV s1. The capacitance of the LPEI-MOx film was comparable with capacitance of pure MOx films of similar mass [42] prepared by cathodic reduction of Mn7+ species in KMnO4 solutions. The capacitance retention (Fig. 10b) at 100 mV s1 was 44%. Turning again to data reported in the literature [41] on chemical precipitation from aqueous solutions it should be noted that the addition of alkali to the Mn2+ solutions results in precipitation of Mn(OH)2, which is gradually oxidized in air and transformed to MnOx. In our approach we used an electrogenerated base instead of alkali. Therefore, it is not surprizing that PC-EPD method resulted in the formation of MnOx. The use of LPEI-Mn2+ for electrosynthesis can potentially limit the size and composition of the particles formed in the LPEI matrix. The use of LPEI-H+ and LPEI-metal ion complexes opens a new an unexplored route in the fabrication of composites, containing functional organic molecules. In this investigation Hb and CD were used as model functional organic materials for the development of different electrochemical strategies, involving the use of LPEI-H+ and LPEI-Mn2+. It is important to note that many organic molecules, such as proteins and enzymes cannot be deposited cathodically or anodically [43] due to their charge reversal in the low pH region at the anode surface or at high pH conditions at the cathode surface. It is known [43] that Hb has an isoelectric point at pH  7. Therefore, in our experiments Hb and LPEI were both positively charged in a mixed solution at pH = 5. An electric field provided electrophoretic transport of Hb and LPEI toward the cathode. The local pH increase at the electrode surface resulted in the charge

Fig. 11. FTIR spectra of (a) LPEI, (b) CD, (c) Hb, (d) deposit prepared from aqueous 1 g L1 LPEI-H+ solution, containing 1 g L1 Hb, (e) deposit, prepared from 1 g L1 LPEI in 5 mM MnCl2 solution, containing 1 g L1 CD.

Fig. 10. (A) CVs at scan rates of (a) 2, (b) 5 and (c) 10 mV s1 and (B) capacitance versus scan rate for the film, prepared from 5 mM MnCl2 solution, containing 0.5 g L1 LPEI.

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of Hb shows absorptions at 1645 and 1535 cm1, which are attributed to amide I band and amide II band [44], respectively. Similar absorptions were observed in the spectrum of the composite LPEIHb films in addition to peaks of LPEI. The FTIR spectrum of CD showed a broad peak centered at 1018 cm1 due to CAOAC vibrations [45]. A similar absorption was observed in the spectrum of the deposit prepared from LPEI-Mn2+ solutions, containing CD. The shift of this peak to 1031 cm1 can result from the polypseudorotaxane formation. The results of FTIR studies confirmed that Hb and CD were incorporated into the LPEI films. In this investigation Hb was used as a model protein for the development of a deposition mechanism. It is expected that a similar approach can be used for the deposition of other proteins and enzymes for diverse applications in biomedical implants and biosensors. CD is a unique carrier [46–48] of various functional organic molecules, therefore CD can facilitate their incorporation into the composite LPEI films. 4. Conclusions The pH-dependent charge and solubility, unique binding and complex-forming properties of LPEI play a vital role in the mechanisms of EPD and PC-EPD. A new EPD method has been developed for the fabrication of composite films containing Mn3O4 and ZnO nanoparticles, as well as advanced flame-retardant materials, such as halloysite nanotubes and memory-type AMZ within the matrix of the water insoluble LPEI. A PELLI method has been developed for the agglomerate-free processing of AMZ particles and efficient extraction was achieved using DPA as an extractor. A conceptually new PC-EPD method has been developed, which is based on the use of LPEI-metal ion complexes. The PC-EPD method allowed for the fabrication of LPEI-Ni(OH)2 and LPEI-MnOx nanocomposites. The composites showed valuable flame retardant and charge storage properties. The unique film forming and chemical properties of LPEI allowed for the development of electrochemical strategies for the fabrication of organic composites using EPD and PC-EPD. Hb was used as a model protein for the fabrication of composite LPEI-Hb films. Another important finding was the possibility of the fabrication of composites, which contain CD, a unique carrier of various functional organic molecules. The development of PCEPD method paves the way for the synthesis of advanced organic-inorganic nanostructures, which cannot be formed by other electrosynthesis techniques [40,49]. Future work can result in the development of new composites, containing other proteins and enzymes for application in biomedical implants and biosensors. EPD and PC-EPD are versatile methods, which will allow for the deposition of novel LPEI based composites containing various functional inorganic materials. Acknowledgement The authors gratefully acknowledge the Natural Sciences and Engineering Research Council of Canada for the financial support and Elna Luckham from the Biointerfaces Institute at McMaster for her assistance with atomic force microscopy (AFM). References [1] C. Chen, B. Feng, S. Hu, Y. Zhang, S. Li, L. Gao, X. Zhang, K. Yu, Control of aluminum phosphate coating on mullite fibers by surface modification with polyethylenimine, Ceram. Int. 44 (1) (2018) 216–224. [2] Z. Gonzalez, C. Filiatre, C.C. Buron, A.J. Sanchez-Herencia, B. Ferrari, Electrophoretic deposition of Ni(OH)2 nanoplatelets modified by polyelectrolyte multilayers: study of the coatings formation in a laminar flow cell, J. Electrochem. Soc. 164 (7) (2017) 436–444. [3] A. Karimi, K.A. Kirk, S. Andreescu, Electrochemical investigation of pHdependent activity of polyethylenimine-capped silver nanoparticles, ChemElectroChem 4 (11) (2017) 2801–2806.

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