Microstructure-controllable nanocomplexes bulk possessed with durable superhydrophobicity

Journal Pre-proofs Microstructure-controllable Nanocomplexes Bulk Possessed with Durable Superhydrophobicity Cheng Chen, Mingming Liu, Yuanyuan Hou, Liping Zhang, Min Li, Dong Wang, Shaohai Fu PII: DOI: Reference:

S1385-8947(20)30411-3 https://doi.org/10.1016/j.cej.2020.124420 CEJ 124420

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Chemical Engineering Journal

Received Date: Revised Date: Accepted Date:

18 October 2019 27 January 2020 10 February 2020

Please cite this article as: C. Chen, M. Liu, Y. Hou, L. Zhang, M. Li, D. Wang, S. Fu, Microstructure-controllable Nanocomplexes Bulk Possessed with Durable Superhydrophobicity, Chemical Engineering Journal (2020), doi: https://doi.org/10.1016/j.cej.2020.124420

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Microstructure-controllable Nanocomplexes Bulk Possessed with Durable Superhydrophobicity Cheng Chen, Mingming Liu*, Yuanyuan Hou, Liping Zhang, Min Li, Dong Wang and Shaohai Fu* Jiangsu Engineering Research Center For Digital Textile Inkjet Printing, Key Laboratory of Eco-Textile, Jiangnan University, Ministry of Education, Wuxi, Jiangsu 214122, China

ABSTRACT: Based on a simple and convenient 1, 4-conjugated addition reaction, a new class of porous nanocomplexes (NCs) bulk was successfully fabricated without the need for a template via a facile gelation process involving dipentaerythritol penta-/hexa-acrylate (5Acl) and branched polyethylenimine ethylenediamine (BPEI), follow by modification with octadecylamine (OTCA). These NCs exhibited a durable superhydrophobicity and various applied performances. The synthesized pile-up granule size was controlled by regulating the addition of the branched agent (BPEI) and the types of reactive solvents. In addition, the microstructure and mechanical properties of the resultant NCs bulk could be adjusted from a soft and loose structure to a rigid and dense structure. To further endow the resultant NCs bulk with more versatile properties, different functional inorganic nanoparticles were compounded into the controlled NCs gel system to construct multifunctional organic/inorganic hybrid NCs bulk. For example, a magnetically controlled NCs bulk used for oil-water separation was prepared by doping magnetic substances into the loose NCs gel. Colored NCs chalk for fabricating a chromatic

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superhydrophobic coating was constructed by mixing nanoscale inorganic pigments into the compact NCs gel. Additionally, a superhydrophobic NCs elastomer was prepared in pentanol and could maintain its anti-wetting property after repeated pressing, as well as store air under water. It is believed that the ability to control the microstructure may promote the development of bulk superhydrophobic porous materials. The constructed multifunctional NCs monolith with robust superhydrophobicity holds promise for fundamental research and practical applications.

KEYWORDS:

Microstructure-controllable;

Nanocomplexes

bulk;

Durable;

Superhydrophobicity. 1. INTRODUCTION An artificial micro- or meso-porous structure that mimics natural porous materials provides a high specific surface area [1-2], which helps to facilitate the application of functional materials, e.g., for purification, drug release, supporting catalysts, and biological mass transfer. Generally, micro- or meso-porous functional materials are obtained by preparing a soft or hard template through a sequence of experimental steps and then removing the template after doping with a solid substance under the special conditions of high-temperature calcination, organic solvent soaking, or chemical corrosion [3-5]. Obviously, the current fabrication routes for porous functional materials are tedious [6], leading to restrictions on their range of applications and operational conditions. Diverse non-wetting phenomena for water droplets on surfaces have already been found in different organisms, such as the low water adhesion of the lotus leaf effect and the high water adhesion of the rose petal effect [7-8]. Inspired by the combination of surface roughness and low surface energy found on natural water-repellent surfaces, many approaches, including top-down

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and bottom-up methods, have been utilized to mimic these special natural surfaces, thereby obtaining man-made functional materials with superhydrophobicity. A variety of artificial superhydrophobic materials (contact angle  150, sliding angle  10) have been fabricated for use in a range of practical applications, including self-cleaning [9-12], microdroplet transportation [13-14], anti-icing [15-16], oil-water separation [17-21], and anti-fouling [22-23]. Actually, the application scope of superhydrophobic porous materials with high specific surface areas can be widened through multi-functionalization, which can make them available for multiple uses in specialized fields such as unidirectional filtration, pollutant disposal, controlledrelease, and directional infiltration. However, the unstable hierarchical micro/nano structure of artificial superhydrophobic porous surfaces and coatings prepared using the existing process can be easily destroyed when the surfaces and coatings are subjected to mechanical damage, leading to the deterioration of their anti-wetting effect and functional performances [24-25]. In order to improve the mechanical robustness of superhydrophobic porous surfaces and coatings, reactive sites for cross-linking within the chemical composition or cross points for physical bonding between structural segments have been introduced to intensify the structural hierarchy

and

low

surface

energy

distribution

[26-27].

However,

the

obtained

superhydrophobicity of these reinforced surfaces and coatings still gradually decreases upon damage to the external layer. Thus, a new class of bulk functional materials with internal and external superhydrophobicity has been designed and prepared in recent years [28-30]. Clearly, the non-wetting property has not been limited to the surface of these bulk functional materials compared to conventional superhydrophobic objects, allowing an all-around anti-wetting property on the inside and outside of the bulk superhydrophobic materials. Thus, even after physical damage to the external layer of such a bulk superhydrophobic material under abrading,

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scratching, or puckering, it is still difficult to wet the damaged bulk by contact with water because of its interior water repellent mechanism [28-29]. Hence, this new class of bulk superhydrophobic materials has potential value in fundamental research and practical applications. Several research groups have developed diverse approaches to obtain inherent three-dimensional superhydrophobicity extended to the entire functional bulk. Men et al. [28] created a superhydrophobic carbon nanotubes-polytetrafluoroethylene (CNTs-PTFE) bulk via a reaction between CNTs and PTFE in a metal mold under the conditions of a high temperature and high pressure. Tiwari et al. [31] fabricated robust and free-standing bulk superhydrophobic composites without fluoride based on a press-in-mold method by doping hydrophobic silica particles in different polymers. This kind of superhydrophobic bulk formed by compression molding could obtain a high mechanical strength, but there were almost no micro- or meso-pores in the bulk materials. Zhong et al. [32] investigated a preparation method to construct waterrepellent renewable cellulose aerogel using a microfibrillation treatment and then freezedrying, which could be used as a highly absorptive material for cleaning up oil spills. It was obvious that the obtained aerogel bulk had a hierarchical porous structure. However, the mechanical structure with ultralow density was easily damaged. Bulk superhydrophobic functional materials with both a porous structure and mechanical robustness have been developed and investigated by researchers. Ramakrishna et al. [33] first grafted silica particles with octadecyl chains under a long-term heating condition. Then, a dispersion of modified silica particles in xylene dripped onto a glass substrate was melted to form the bulk superhydrophobic porous coating over a long period. Zhang et al. [34] fabricated a bulk superhydrophobic polymer using the confined polymerization of divinylbenzene mixed with silica particles under a high-temperature condition, which exhibited a high specific surface area

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and large pore volume. However, it is noticeable that most existing methods for fabricating bulk superhydrophobic porous materials involve process complexity, strict operational conditions, tedious steps, and time-consuming reactions. Additionally, so far, there have been a limited number of feasible approaches used for realizing the efficient fabrication of a superhydrophobic porous bulk. Thus, further study is needed. Recently, by utilizing the reaction between the acrylate group and amino group, Manna et al. [35-36] synthesized a new kind of polymeric gel to construct superhydrophobic porous particulate coatings and loose bulk materials. However, in spite of discussing the impacts of alkylamine containing different alkyl chain lengths on the wettability, the inability to control the dimensions of the structure and mechanical properties of the prepared novel water-repellent polymer resulted in the display of only a single function on application. In the present study, superhydrophobic porous nanocomplexes (NCs) bulk was fabricated without using a template by means of gelation between dipentaerythritol penta-/hexa-acrylate (5Acl) and branched polyethylenimine ethylenediamine (BPEI), followed by wet-chemical modification with octadecylamine (OTCA) under room temperature conditions. These chemical processes were carried out via a simple and convenient 1, 4-conjugated addition reaction. Furthermore, the size of the pile-up granules in the NCs bulk was regulated by adjusting the amount of the branched agent (BPEI) added and the types of reactive solvents, making it possible to control the structural density and voids caused by gaps between NCs granules. Thereby, different microstructural NCs bulks, from loose to dense materials, were obtained and had diverse mechanical characteristics from soft to rigid. Based on the microstructure-controllable NCs bulk formed in absolute ethanol, magnetically controlled bulk NCs for use in oil-water separation and colored NC chalk used for fabricating chromatic superhydrophobic coatings were

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prepared by doping unbranched nanocomplexes (UNCs)-modified Fe3O4 or nanoscale inorganic pigments in polymeric NCs gels with various BPEI ratios, respectively. In addition, a superhydrophobic NCs elastomer could be fabricated in pentanol. By regulating and controlling the polymeric gel system, the as-prepared multifunctional organic/inorganic hybrid NCs bulk doped with functional inorganic nanoparticles had a robust superhydrophobicity and various applied performances, which showed their promise for a diverse range of scientific studies and industrial applications.

2. EXPERIMENTAL SECTION 2.1. Materials Dipentaerythritol

penta-/hexa-acrylate

(5Acl,

98%),

branched

polyethylenimine

ethylenediamine (BPEI, 98%), octadecylamine (OTCA, 98%), ferroferric oxide (Fe3O4, 30 nm) and aminopropyltriethoxysilane (APTES, 98%) were supplied by the Shanghai Macklin Biochemical Co. Absolute ethanol (99.7%), n-amyl alcohol (98%), and tetrahydrofuran (THF, 98%) were supplied by the Sinopharm Chemical Reagent Co. Analytical grade isooctane (98%), n-hexane (98%), chloroform (98%), dichloroethane (98%), dichloromethane (98%), sodium chloride, NaOH, and HCl (38%) were purchased from the Shanghai Chemical Reagent Co. Chrome green (CRG) was purchased from the Inner Mongolia Yellow River Chrome Salt Co. Iron Red (IR) was purchased from the Hangzhou Lihe Pigment Co. Prussian blue (PB) was purchased from the Shanghai Guandao Biological Engineering Co. 2.2. Preparation of NCs bulk First, 5Acl and BPEI were added to 10 mL of absolute ethanol to obtain a mixture, where the amount of 5Acl was maintained at 1.5 g, and the 5Acl:BPEI molar ratio was changed to 7:1,

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5:1 or 4:1. Then, the mixture was placed in a room temperature environment for a couple of minutes, over which time the liquid phase first became turbid, and then a milky-white polymeric gel was obtained as a result of the gelation between the 5Acl and BPEI via the 1, 4-conjugated addition reaction. After that, the prepared milky-white polymeric gel was added to 15 mL of THF containing 1.5 g of OTCA, and its hydrophobic modification was implemented for 24 h at room temperature. Finally, the microstructure-controllable NCs bulk was obtained, with the preparation route shown in Scheme 1.

Scheme 1. (a) The gelation reaction of 5Acl and BPEI in ethanol, (b) reaction principle of NCs, (c) NCs bulk after hydrophobic modification. 2.3. Synthesis of UNCs-modified Fe3O4 First, 50 mL of deionized water and 0.5 g of Fe3O4 were charged into a three-neck flask. Then, an NaOH aqueous solution (2 M) was added to the above solution to adjust the pH value

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to 9.5. Hydroxylation occurred, and it was kept at 60 °C for 3 h. Subsequently, the solution pH was adjusted to 4 by adding glacial acetic acid after 50 mL of absolute ethanol was charged into the above system. Immediately, 1.4 mL of aminopropyltriethoxysilane (APTES) was added to introduce amino groups on the surface of the Fe3O4. The mass ratio of the amino-functionalized Fe3O4:5Acl:OTCA was maintained at 1:6:6, and after adding 30 mL of THF, the modification of the UNCs was performed at 25 °C for 12 h. Finally, the UNCs-modified Fe3O4 was synthesized. 2.4. Fabrication of magnetic NCs bulk and colored NCs chalk The self-made UNCs-modified Fe3O4 (based on the weight of BPEI, 40 wt%) was mixed with 5Acl and BPEI in ethanol to form a magnetic bulk structure, with the molar ratio of 5Acl and BPEI set at 7:1. Inorganic pigments, including CRG, IR, and PB (0.2 g) were mixed with 5Acl and BPEI in ethanol to form colored chalk structures, where the molar ratio of 5Acl and BPEI was set at 5:1. The magnetic NCs bulk and colored NCs chalk were fabricated via the same method used for the preparation of the NCs bulk in absolute ethanol. 2.5. Fabrication of pentanol-based NCs bulk The reaction between 5Acl and BPEI was carried out in pentanol to form a polymeric structure, with various molar ratios for 5Acl and BPEI, including 7:1, 5:1, and 4:1. The pentanolbased NCs bulk-1, 2, and 3 were fabricated via the same method used for the preparation of the NCs bulk in absolute ethanol. 2.6. Characterization and measurements The characterization of the microstructure and element composition of each sample was carried out via a scanning electron microscope (SEM) apparatus (su1510, Hitachi) with energy dispersive spectrum (EDS). The voidage of each sample was tested using a true density meter (AccuPyc II 1340, Micromeritics). The BET specific surface area and pore volume of each

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sample were characterized using a full-automatic specific surface area and porosity analysis meter (TriStar II 3020, Micromeritics). The compressive stress-strain curves of the samples were tested via an electronic universal testing machine (Criterion40, MTS Systems). The rigidities of the samples were measured using a Shaw hardness tester (HLX-AC, HANDPI). The chemical bonds and functional groups of the samples were measured using infrared spectroscopy (iS50FTIR, Thermo Fisher). The X-ray diffraction (XRD) of each sample was tested utilizing an X-ray diffractometer with monochromatic Cu Kα radiation (D2 ADVANCE, Bruker). The contact angles of static water droplets (5 μL) to the samples and the sliding angles of dynamic water droplets (10 μL) to the samples were all measured using a contact angle meter equipped with a CCD camera (JC2000D1, Powereach) at room temperature. The bouncing process when a water droplet (5 μL) fell on the sample surface was captured using a high-speed camera (LC321S, Phantom), which was also used to capture the oil-absorbing process of a falling n-hexane droplet (10 μL) on the sample surface. The oil-absorption efficiency (, %) of the superhydrophobic bulk was calculated using the following equation:  = [(m1-m0)/m2]  100%, where m0 is the original mass of the bulk, m1 represents the total mass of the bulk after absorbing oil, and m2 denotes the mass of the oil in the oil-water mixture. An abrasion resistance test of a fabric sample was implemented by repeatedly dragging it 10 cm across sandpaper (mesh number, 1000) for 100 cycles, and the load bearing of the fabric sample was 100 g. Meantime, the wettability of the fabric sample was tested each 10 cycles.

3. RESULTS AND DISCUSSION 3.1. Control of BPEI on microstructure for NCs bulk

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The gelation reaction of 5Acl and BPEI in absolute ethanol could be carried out. Thus, the structure of the obtained polymeric gel network was mainly governed by the amount of the branched agent (BPEI). Evidently, the granular structure scale of the NCs bulk gradually decreased with an increase in the amount of BPEI. Meanwhile, the microstructure of the NCs bulk formed from pile-up granules in the NCs inevitably tended to densify (Figure 1a-c). Moreover, Figure S1a showed that the density of the NCs bulk significantly increased while its voidage quickly decreased during the densification trend caused by increasing the added BPEI content. Compared to loose NCs bulk-1 (density = 0.2442 g/cm3, voidage = 93.47 %), the density of dense NCs bulk-3 after drastic shrinkage sharply increased to 0.9549 g/cm3 and the voidage substantially decreased to 16.63 %. Additionally, the nitrogen adsorption-desorption isotherms and pore width distribution of the NCs bulk when increasing the BPEI ratio were investigated to verify the microstructure regulation of the NCs bulk-1, 2, 3 (Figure S2a-b). Figure S2c indicated that the specific surface area (9.9299 m2/g) and pore volume (0.009142 cm3/g) of NCs bulk-2 were apparently higher than those of NCs bulk-1 (specific surface area = 3.1169 m2/g, pore volume = 0.002345 cm3/g). This was attributed to a significant decrease in the scale of the NCs pile-up granules from NCs bulk-1 to NCs bulk-2. In addition, the BPEI ratio in NCs bulk-2 was conducive to facilitating pore formation in the NCs pile-up granules. Nevertheless, NCs bulk-3 achieved an extremely low specific surface area (0.7851 m2/g) and pore volume (0.000226 cm3/g), confirming the densified agglomeration trend in the microstructure of a NCs bulk containing an excessive BPEI ratio. As shown in Figure S3, from NCs bulk-1 to NCs bulk-3, the compressive stress-strain curves evidently became steeper, illustrating that the elasticity modulus of the NCs bulk gradually enhanced with increasing of the amount of BPEI, which resulted in the tendency for the NCs bulk to become rigid when the BPEI

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ratio increased. Meanwhile, the rigidity of the NCs bulk increased from 32 HSC to 77 HSC under the densification trend (Figure S1b), further indicating that the mechanical strength of the obtained NCs bulk could be controlled by adjusting the added amount of BPEI. As seen in the XRD data for the different NCs bulk controlled by changing the added amount of BPEI (Figure S1c), the XRD peaks of NCs bulk-1 to NCs bulk-3 moved from 19.92 to 22.58, with the crystallinity decreasing from 50.76 % to 30.78 %, confirming the increase in the branching degree from NCs bulk-1 to NCs bulk-3, as well as the densification of the NCs bulk. The reaction sites of 5Acl were not completely occupied when the added amount of BPEI was low. Thus, the gelation reaction between 5Acl and BPEI was performed to create NCs granules with a large scale under continuous crosslinking. When the amount of added BPEI was increased, the active sites of 5Acl were thoroughly blocked by the high amount of BPEI, leading to a decrease in the size of the formed NCs granules, which further resulted in an intergranular densification pileup (Figure S1d). As shown in Figure 1d, the infrared absorption peaks of the characteristic functional groups of the microstructure-controllable NCs bulk, such as the C-C bond (peaks at around 2917 cm-1 and 2849 cm-1), the ester bond (peak at around 1731 cm-1), the N-H bond (peak at around 1465 cm-1) and the C-N bond (peak at around 1160 cm-1), all appeared in the fourier transform infrared-attenuated total reflection (FTIR-ATR) spectra. According to the results for the areas of the spectral peaks in the FTIR-ATR spectra calculated by the Origin 8.5 software, the peak area ratio of the N-H bond and C-N bond in the FTIR-ATR spectra of the NCs bulk, which represented the target peak intensity, exhibited an escalating trend with an increase in the amount of BPEI (Figure S4). Because of the lipophilicity and hydrophobicity found in the as-prepared NCs bulk, the maximum oil-absorption capacities of the three kinds of the NCs bulk were measured. It was found that the maximum oil-absorption capacity of the NCs bulk

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decreased from 1.8936  0.0238 g/g (NCs bulk-1) to 0.0940  0.0082 g/g (NCs bulk-3), when the amount of added BPEI increased (Figure 1e). Figure 1f-h showed that when falling water droplets (5 μL) touched the various prepared NCs bulk surfaces, they bounced and formed spherical shapes, exhibiting superior water-repellency. In sharp contrast to this excellent waterbouncing capacity, oil droplets (n-hexane, 10 μL) easily infiltrated and spread on the surfaces of the NCs bulk with different microstructures (Figure 1i-k). Furthermore, loose NCs bulk-1 could absorb the n-hexane into the internal bulk in 21 ms, which was a shorter oil-absorption time than those exhibited by the other prepared NCs bulk, showing its remarkable lipophilicity and strong oil absorbency. The increase in the oil-absorption time further confirmed the densification trend for the microstructures of the NCs bulk with an increasing BPEI ratio.

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Figure 1. Microstructure of (a) NCs bulk-1, (b) NCs bulk-2 and (c) NCs bulk-3, (d) FTIR-ATR spectra and (e) oil-absorption (n-hexane) of various NCs bulks, water bouncing behavior of (f) NCs bulk-1, (g) NCs bulk-2, (h) NCs bulk-3, oil absorbing behavior (n-hexane) of (i) NCs bulk-1, (j) NCs bulk-2, (k) NCs bulk-3. 3.2. Control of reactive solvent on microstructure for NCs bulk To determine how the performances differed from those of the previously mentioned NCs bulk formed in absolute ethanol, the influences of reactive solvents on the granular structure of the NCs during the gelation formation were further researched. Polymeric NCs gel was prepared in pentanol, after which the different microstructures of the NCs granules were viewed using SEM observations. Figure 2a-c showed that the NCs granular structure had the same densification trend as the previously discussed absolute ethanol-based NCs bulk with an increase in the amount of added branched agent (BPEI), whereas the granule sizes of the as-prepared pentanol-based NCs bulks were all higher than those of the corresponding absolute ethanol-based NCs bulks, indicating that the formation process for the NCs pile-up granules in pentanol was different from that in absolute ethanol. From Figure 2d, it could be seen that the infrared

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characteristic absorption peaks of the functional groups originating from the NCs composition were all present in the FTIR-ATR spectra for the three kinds of pentanol-based NCs bulks, including the C-C bond (peaks at around 2916 cm-1 and 2849 cm-1), the ester bond (peak at around 1732 cm-1), the N-H bond (peak at around 1465 cm-1) and the C-N bond(peak at around 1160 cm-1), confirming that pentanol did not affect the chemical composition and functional groups of the formed NCs. Based on calculations using the via Origin 8.5 software, Figure S5 showed that the peak area ratio (representing the peak intensity) of the N-H bond and C-N bond in the FTIR-ATR spectra for the pentanol-based NCs bulk also appeared to increased with the BPEI ratio in the pentanol system. In contrast, the XRD spectra for the pentanol-based NCs bulks showed sharp X-ray diffraction peaks at 22 (Figure 2e), with the sharpness higher than that for the NCs bulks formed in absolute ethanol. This indicated that the as-prepared pentanolbased NCs bulks were well-crystallized compared to the absolute ethanol-based NCs bulks. This was because the well-crystallized pentanol-based NCs bulks had larger crystal grains and internal point particles with a regular arrangement. Moreover, the crystallinity of the pentanol-based NCs bulks decreased from 54.17 % to 31.86 % when the amount of added BPEI was increased, with crystallinities that were greater than those of the corresponding absolute ethanol-based NCs bulks, suggesting that it was not conducive for the effective branching reaction of the NCs pileup granules to be carried out when the reactive solvent was pentanol. In order to further determine the impacts of the branched agent (BPEI) on the physical performance of the NCs bulk obtained in pentanol, the density, voidage, and rigidity values of different pentanol-based NCs bulks were measured, as shown in Figure S6. With an increase in the amount of BPEI participating in the pentanol-based NCs formation, the density of the prepared pentanol-based NCs bulks increased from 0.2278 g/cm3 to 0.6093 g/cm3, whereas the voidage decreased from

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84.92 % to 51.19 %, showing that the pentanol-based NCs bulk tended toward a densification state (Figure S6a). As seen in the nitrogen adsorption-desorption isotherms and pore width distribution of pentanol-based NCs bulk-1, 2, 3 (Figure S7a-b), when the BPEI ratio increased in the pentanol system, the specific surface area and pore volume gradually increased (Figure S7c). Meanwhile, pentanol-based NCs bulk-3 with a high BPEI ratio still had a larger specific surface area (29.5767 m2/g) and pore volume (0.031167 cm3/g) than pentanol-based NCs bulk-1, 2, which was caused by the obvious decline in the size of the NCs pile-up granules, as well as the suitable BPEI ratio being conducive to pore formation in the pentanol system. From pentanolbased NCs bulk-1 to pentanol-based NCs bulk-3, the compressive stress-strain curves steepened with an increase in the amount of BPEI in the pentanol system (Figure S8). Thus, continuously increasing elasticity modulus caused the apparent characteristic of rigidification in the pentanolbased NCs bulk. Meanwhile, the rigidity of the NCs bulk formed in pentanol increased from 24 HSC to 59 HSC (Figure S6b), reconfirming that a densification trend occurred in the microstructure of the pentanol-based NCs bulk. As shown in Figure S6c, the migration of BPEI molecular chains in pentanol with a high viscosity was hindered form extending the length of the BPEI chains. This caused an increase in the occupied chemical space for active sites between BPEI and 5Acl, and then produced pile-up granules with a larger scale compared to the absolute ethanol-based NCs granules. Just as important, the branching reaction rate of BPEI to 5Acl in the viscous solvent system decreased, causing the branching degrees of the pentanol-based NCs bulks to be lower than those of the corresponding absolute ethanol-based NCs bulks. This showed the overall increase in the crystallinities of the NCs bulk obtained in pentanol. Therefore, the physical and chemical performances displayed by the pentanol-based NCs bulk were different from those of the NCs bulk formed in absolute ethanol. Additionally, the as-prepared

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pentanol-based NCs bulk could all achieve strong superhydrophobicity (contact angle  160, sliding angle  5) (Figure 2f).

Figure 2. Microstructure of (a) pentanol-based NCs bulk-1, (b) pentanol-based NCs bulk-2 and (c) pentanol-based NCs bulk-3, (d) FTIR-ATR spectra, (e) XRD spectra and (f) wettability of different pentanol-based NCs bulks. 3.3. Characterization and performance of magnetic superhydrophobic NCs bulk

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To endow the NCs bulk with magnetism, nanoscale Fe3O4 was selected as a magnetic filler and doped into the sol reaction system between 5Acl and BPEI before the gelatinization and hydrophobic modification. Because the nanoscale Fe3O4 had inherent hydroxyl groups, the hydrophobization of the nanoscale Fe3O4 helped to avoid the effect of an introduced hydrophilic component on the wettability of the as-prepared NCs bulk. The hydrophobic treatment of the nanoscale Fe3O4 was implemented via amino-functionalization of the Fe3O4, followed by the insitu growth of UNCs (5Acl-OTCA without BPEI) on the amino-functionalized Fe3O4 (Figure S9a). Figure S9b-d showed that the N and Si element contents of the nanoscale Fe3O4 increased from 0.91 % and 0.20 % to 13.67 % and 9.17 %, respectively, after amino-functionalization, whereas the contact angle decreased from 58 to 14, indicating that amino groups were successfully grafted onto the nanoscale Fe3O4. The N and Si element contents of the aminofunctionalized Fe3O4 were decreased from 13.67 % and 9.17 % to 1.93 % and 1.49 %, respectively, via the UNCs modification treatment. Meanwhile, its C element content increased to 44.85 %, with the contact angle increasing from 14 to 150, revealing that OTCA with a long alkyl chain was introduced into the amino-functionalized Fe3O4 with the help of the 1, 4conjugated addition reaction with participation by 5Acl. Figure S9e showed that infrared absorption peaks for the N-H bond (peak at 1652.24 cm-1), the Si-O-Si bond (peak at 1008.12 cm-1) and the Fe-O bond (peak at 519.14 cm-1) appeared in the FTIR-ATR spectra of the aminofunctionalized Fe3O4 formed from the modification of Fe3O4 using the silane coupler APTES. After the 1, 4-conjugated addition reaction of 5Acl and OTCA on the amino-functionalized Fe3O4, the FTIR-ATR spectra of the UNCs-modified Fe3O4 showed the infrared characteristic absorption peaks of the synthesized UNCs, including the C-C bond (peaks at 2918.78 cm-1 and 2849.84 cm-1), the ester bond (peak at 1733.24 cm-1), and the C-N bond (peak at 1204.83 cm-1).

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Furthermore, the XRD diffraction peak of the UNCs at 19 appeared on the XRD spectra of the UNCs-modified Fe3O4, confirming the in-situ formation of UNCs on the nanoscale Fe3O4 (Figure S9f). The as-prepared hydrophobic UNCs-modified Fe3O4 was doped as a magnetic filler in the formation process of the polymeric gel system to obtain lightweight magnetic superhydrophobic NCs bulk, which possessed a high contact angle (167), low sliding angle (2), and strong waterimpact resistance (Figure 3a-b). Roughened polymeric granules could be seen in the microstructure of the magnetic NCs bulk, as shown in Figure 3c and S10. This microstructure roughening was caused by the random distribution of UNCs-modified Fe3O4 during the formation of NCs granules. Figure S11a showed that the infrared absorption peak of the Fe-O bond (peak at 537.57 cm-1) that originated from the UNCs-modified Fe3O4 existed in the FTIRATR spectra of the prepared magnetic NCs bulk. Meanwhile, XRD diffraction peaks of the UNCs-modified Fe3O4 at 2 of 35, 56, and 62 also existed in the XRD spectra of the magnetic NCs bulk, evidently demonstrating that a stable composite between the NCs and UNCs-modified Fe3O4 was realized to form NCs bulk with magnetism (Figure S11b). Moreover, the Fe element content (1.46 %) was found in the atomic EDS mapping data of the magnetic NCs bulk (Figure 3d), showing the stable compounding system of the UNCs-modified Fe3O4 and NCs bulk. Obviously, the magnetic NCs bulk grafted with long alkyl chains had a high C element content (90.06 %). Figure 3e showed that a water droplet could completely detach from the surface of the magnetic NCs bulk after water droplet declining and then upward separating. An evident air pocket layer distributed on the magnetic NCs bulk was observed when it was submerged in water, after which the magnetic NCs bulk rose to the water surface to achieve a floating state with nonwetting (Figure 3f). The lightweight magnetic superhydrophobic NCs bulk floated on the water,

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and their movement track could be controlled by the orientation of a magnet (Figure 3g), indicating the realization of remote-control for the prepared magnetic superhydrophobic NCs bulk.

Figure 3. (a) Magnetic NCs bulk with superhydrophobicity and lightweight, (b) water-impact resistance, (c) microstructure, (d) atomic EDS mapping, (e) water adhesion behavior, (f) floating state and (g) magnetic control process of magnetic NCs bulk.

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To determine the oil-absorbing ability of the magnetic superhydrophobic NCs bulk, the maximum oil-absorption and cyclic oil-absorption values of NCs bulk-1 without or with UNCsmodified Fe3O4 were measured after immersion in light and heavy oil. Figure 4a-d showed that the maximum oil-absorption and cyclic oil-absorption values of the magnetic NCs bulk were all higher than those of NCs bulk-1 without UNCs-modified Fe3O4. Meanwhile, the cyclic oilabsorption and superhydrophobicity of the magnetic NCs bulk showed little adverse effect during repeated immersion in n-hexane for 10 times, showing properties that were superior to those of NCs bulk-1. In addition, the oil-absorption efficiencies of the magnetic NCs bulk in various light or heavy oil-water mixtures were all more than 90 % (Figure S12a). Moreover, the cyclic oil-absorption efficiency for n-hexane or dichloromethane still remained above 92 % or 95 %, respectively (Figure S12b). The strengthening mechanism of the oil-absorbing ability and water-repellency of the magnetic NCs bulk were attributed to the increases in the specific surface area and pore volume caused by the composite of UNCs-modified Fe3O4 and the formed NCs pile-up granules. The BET data from Figure S13 demonstrated that the specific surface area (3.1423 m2/g) and pore volume (0.002427 cm3/g) of the magnetic NCs bulk were slightly higher than those of NCs bulk-1 (specific surface area = 3.1169 m2/g, pore volume = 0.002345 cm3/g). As seen in Figure 4e, although there was a certain distance between the magnetic NCs bulk and edible oil floating on water, the bulk controlled by the magnet could move into contact with the edible oil and completely absorb it, indicating that the magnetic NCs bulk had a good magnetic control capacity. Figure 4f showed that when the magnetic superhydrophobic NCs bulk was used in a vacuum suction valve, it successfully separated the n-hexane floating on brine (3.5 %), realizing the extensive absorption of an oil slick under a pressure-driven condition. Hence, the as-prepared magnetic NCs bulk could be used in special valves to assemble oil-water separation

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devices, overcoming the problem of limited maximum oil-absorption in such a magnetic bulk. In addition, sinking dichloromethane was also easily absorbed into the submerged magnetic NCs bulk (Figure 4g). Therefore, it was believed that the magnetic superhydrophobic NCs bulk held promise for oil-water separation and environmental governance applications.

Figure 4. (a) Maximum oil-absorption, (b) cyclic oil-absorption (n-hexane) of NCs bulk-1 and magnetic NCs bulk, wettabiliy of (c) magnetic NCs bulk and (d) NCs bulk-1 after repeatedly absorbing n-hexane, (e) directed absorbing of light oil (edible oil) using magnetic control, (f) oilwater separation process, (g) absorbing of heavy oil (dichloromethane).

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However, the as-prepared magnetic NCs bulk inevitably suffered various extreme situations when in use. Thereby, the influences of extreme conditions on the wettability of the magnetic NCs bulk should be discussed in detail. Based on the results in Figure 5a, it could be seen that the contact angles and sliding angles of the magnetic NCs bulk after soaking in an alkali liquid (pH 13), an acid liquid (pH 1), a brine (3.5 %), or dichloromethane for 12 h still remained in the state of superhydrophobicity (contact angle  150, sliding angle  10), showing that the magnetic NCs bulk had high resistances to soaking treatment. Furthermore, as shown in Figure 5b, the contact angles of water with different pH values on the surface of the magnetic NCs bulk were all higher than 165, with sliding angles lower than 5. In addition, when the magnetic NCs bulk was treated by heating (90 C) or radiating (UV light) for 12 h, the treated bulk still had high contact angles ( 165) and low sliding angles ( 5) (Figure 5c-d). Based on the above results, the magnetic NCs bulk maintained strong water-repellency under a variety of extreme conditions, thus indicating that the superhydrophobic magnetic NCs bulk had good chemical stability.

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Figure 5. Wettability of magnetic NCs bulk under conditions of (a) soaking treatment for 12 h, (b) different pH value, (c) heat treatment (90 C) for 12 h, (d) UV radiation for 12 h. 3.4. Applied properties of colored superhydrophobic NCs chalk NCs bulk-2, which had a densified microstructure due to the size shrinkage of the NCs pileup granules, had a chalklike appearance and hardness. Thus, it could be used as a superhydrophobic chalk (Figure 6a). As shown in Figure 6b-e, the obtained superhydrophobic NCs chalk with an extremely high C element content could endow hydrophilic latex gloves and leather with a strong water-repellency after repeated rubbing using the chalk. When the angle between the water stream and latex gloves was 50 or 15 and the flow rate of the water stream was 0.16 m/s or 0.31 m/s, two water sputtering columns could clearly be seen (Figure 6d). Meanwhile, the frictional superhydrophobic NCs chalk powder was still stably distributed on the leather surface even after water impact. At present, the multi-functionalization of textiles through

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a series of technological means is the main development trend for the entire textile industry transformation. Thereby, numerous industrial textiles, medical textiles, protective textiles, etc. are successively being fabricated for applications in many fields. However, based on the existing methods for textile treatment, both the coloration and water-repellent treatments of hydrophilic fabrics are difficult to accomplish using a simple route. In view of this, nanoscale inorganic pigments, including CRG, IR, and PB, were used in the gelatinization formation of NCs bulk-2 to fabricate superhydrophobic NCs chalks with three-primary colors, while simultaneously endowing hydrophilic fabric with various color hues and a strong water-repellency by means of the same rubbing method (Figure 6f). Chemical information for the as-prepared NCs/CRG chalk was obtained via FTIR-ATR and XRD measurements (Figure S14). The FTIR-ATR spectra and XRD spectra of the NCs/CRG chalk showed an infrared absorption peak for the Cr-O bond at 561.19 cm-1 and an XRD diffraction peak for NCs bulk-2 at 20.55, which showed that the pigmented chalk was composed of the NCs and nanoscale pigments. As shown in Figure 6h, the different color coated fabrics obtained by rubbing the NCs/CRG, NCs/IR, and NCs/PB chalks on fabric surfaces achieved higher contact angles ( 165) and lower sliding angles ( 5). Beyond that, the superior superhydrophobicity of the obtained color coated fabrics was attributed to the formation of a nanoscale rough surface structure on the fabric, with the help of the uniform distribution of composite pile-up granules rubbed from the pigmented NCs chalk (Figure 6g and S15). As seen in Figure 6i, after dripping water on the fabric, dirt stained on the frictional NCs coated fabric could easily be removed along with the water droplets, allowing a thorough cleaning to be achieved, and demonstrating that the hydrophilic fabric coated with the superhydrophobic NCs chalk had a self-cleaning performance. Moreover, coffee, milk tea, and juice droplets dripped on the fabric could not infiltrate and spread on the fabric after it was

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rubbed with the NCs/CRG, NCs/IR, or NCs/PB chalk. The droplets swiftly slid off without any liquid residue remaining, thus showing the excellent anti-fouling capacity (Figure 6j-l). During a 100 abrasion cycles test of the color coated fabric faced down on sandpaper (mesh number, 1000) under a load of 100 g, the contact angle mildly decreased from 168 to 160, and the sliding angle slightly increased from 3 to 9. Furthermore, after 100 high-strength abrasion cycles, the color coated fabric did not show significant damage (Figure S16). This revealed that the superhydrophobic color coated fabric obtained from repeated rubbing with the pigmented NCs chalk possessed a certain level of abrasion resistance.

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Figure 6. (a) Microstructure and appearance, (b) atomic EDS mapping, (c) wettability of NCs chalk, water-repellency of (d) latex gloves and (e) leather after repeated rubbing using NCs chalk, (f) colored superhydrophobic fabric treated by NCs/CRG chalk, NCs/IR chalk and NCs/PB chalk, (g) microstructure of NCs/CRG chalk, (h) wettability of NCs/CRG, NCs/IR and NCs/PB coated fabric, (i) self-cleaning property of NCs coated fabric, anti-fouling property of (j) NCs/CRG, (k) NCs/IR and (l) NCs/PB chalk. 3.5. Performance evaluation of superhydrophobic NCs elastomer To estimate the possibility of using the obtained pentanol-based NCs bulk-1 as a superhydrophobic polymeric elastomer, its elastic property and wettability were investigated in detail. Figure 7a showed that a certain degree of deformation appeared in the NCs elastomer under pressing (with a downward force of 15 N). Moreover, the deformation of the pressed NCs elastomer rapidly recovered in 0.89 s when the pressure was removed. Furthermore, the NCs elastomer could still maintain its superhydrophobicity with a high contact angle ( 160) and low

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sliding angle ( 5) during 50 repetitions of cyclic pressing (Figure 7b). The water droplets easily rolled off the surface of the tilted NCs elastomer (tilt angle, 5) whether or not it was squeezed (Figure 7c-d). In the meantime, dripping water was not able to wet the squeezed NCs elastomer (Figure 7e), showing that the as-prepared NCs elastomer possessed a durable elasticity and strong water-repellency. When the immersed NCs elastomer suffered squeezing, continuous bubbling was seen on the pressed elastomer surface, followed by deformation recovery of the immersed NCs elastomer after removing the squeezing. Additionally, the superhydrophobicity of the NCs elastomer could still be maintained after squeezing underwater, with a contact angle of 161 and a sliding angle of 5 (Figure 7f). This indicated that the superhydrophobic NCs elastomer with a fluffy structure could store air underwater, which showed that it was a promising candidate for an underwater air receiver with superaerophilicity.

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Figure 7. (a) Deformation and then recovery of NCs elastomer, (b) wettability of NCs elastomer after cyclic pressing, water droplets slid off from NCs elastomer (c) before and (d) after squeezing (tilt angle, 5), squeezing of NCs elastomer in (e) air or (f) water.

4. CONCLUSION Various structural NCs bulks were fabricated in absolute ethanol via a simple and convenient 1, 4-conjugated addition reaction by controlling the molar ratios of the branched agent (BPEI) in the gelation process between 5Acl and BPEI. This made it possible to obtain superhydrophobic NCs bulks with controlled microstructures after modifying the synthesized polymeric gel with OTCA at room temperature. Based on the relevant findings on controlling the structure of absolute ethanol-based NCs bulk, UNCs-modified Fe3O4 was mixed with a loose NCs gel to prepare magnetic superhydrophobic NCs bulk, which could be applied to oil-water separation under magnet control. Additionally, NCs bulk-2 containing nanoscale inorganic pigments was used as a superhydrophobic colored chalk to endow solid substrates with a strong water-repellency and color hue by simply utilizing repeated rubbing. In addition, pentanol-based NCs bulk-1 with an elastic property was found and used in a superhydrophobic elastomer application. To summarize, the microstructure-controllable NCs bulk formed in absolute ethanol or pentanol all had a durable superhydrophobicity and could potentially be applied in various areas such as oil-water separation, self-cleaning coatings, colored anti-fouling surfaces, waterrepellent elastomers with deformation recovery, and underwater air receivers.

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ASSOCIATED CONTENT Supporting Information. Density and voidage, rigidity, XRD spectra, control mechanism of microstructure-controllable NCs bulk via adjusting the amount of BPEI; nitrogen adsorptiondesorption isotherms, pore width distribution, BET specific surface area, pore volume, compressive stress-strain curve, peak area ratio of the N-H bond and the C-N bond in FTIR-ATR spectra of NCs bulk-1, 2, 3; peak area ratio of the N-H bond and the C-N bond in FTIR-ATR spectra, nitrogen adsorption-desorption isotherms, pore width distribution, BET specific surface area, pore volume, compressive stress-strain curve of pentanol-based NCs bulk-1, 2, 3; density and voidage, rigidity, control mechanism of different pentanol-based NCs bulk prepared by controlling amount of BPEI; EDS data, contact angle, FTIR-ATR spectra, XRD data of Fe3O4, amino-functionalized Fe3O4 and UNCs-modified Fe3O4, XRD data of UNCs (without BPEI); surface morphology of polymeric pileup-granules in NCs bulk-1, magnetic NCs bulk and UNCsmodified Fe3O4; FTIR-ATR spectra and XRD spectra of magnetic NCs bulk; oil-absorption efficiency, cyclic oil-absorption efficiency (n-hexane or dichloromethane), nitrogen adsorptiondesorption isotherms, pore width distribution, BET specific surface area and pore volume of magnetic NCs bulk; FTIR-ATR spectra and XRD spectra of NCs/CRG chalk and CRG; surface morphology and atomic EDS mapping of NCs/CRG coated fabric; wettability of NCs/CRG coated fabric during abrasion cycles test. The Supporting Information is available free of charge on the website at DOI: AUTHOR INFORMATION Corresponding Author

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E-mail: [email protected] (Shaohai Fu); E-mail: [email protected] (Mingming Liu). Notes The authors declare no competing financial interest. ACKNOWLEDGMENT This work was supported by the Fundamental Research Funds for the Central Universities [grant numbers JUSRP51907A, JUSRP11916, JUSRP21933]; and Postgraduate Research & Practice Innovation Program of Jiangsu Province [grant numbers KYCX18_1827]. We also thank Jiangnan University for supporting the course of research. REFERENCES [1] C.M. Parlett, K. Wilson, A.F. Lee, Hierarchical Porous Materials: Catalytic Applications, Chem. Soc. Rev. 42 (2013) 3876-3893. 10.1039/c2cs35378d. [2] Y. Li, Z.Y. Fu, B.L. Su, Hierarchically Structured Porous Materials for Energy Conversion and Storage, Adv. Func. Mater. 22 (2012) 4634-4667. https://doi.org/10.1002/adfm.201200591. [3] M.T. Gokmen, F.E. Du Prez, Porous Polymer Particles-A Comprehensive Guide to Synthesis, Characterization, Functionalization and Applications, Prog. Polym. Sci. 37 (2012) 365-405. https://doi.org/10.1016/j.progpolymsci.2011.07.006. [4] H. Sai, K.W. Tan, K. Hur, E. Asenath-Smith, R. Hovden, Y. Jiang, M. Riccio, D.A. Muller, V. Elser, L.A. Estroff, S.M. Gruner, U. Wiesner, Hierarchical Porous Polymer Scaffolds from Block Copolymers, Science 341 (2013) 530-534. 10.1126/science.1238159.

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☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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Highlights:  Superhydrophobic porous NCs bulk was fabricated without using a template.  Control on microstructure of NCs bulk was realized.  Doped NCs bulk had durable superhydrophobicity and various applications.

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