Amphiphobic Nanocellulose-Modified Paper

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Amphiphobic nanocellulose-modiﬁed paper: fabrication and evaluation† Cite this: RSC Adv.,2016,6,13328 Patchiya Phanthong,a Guoqing Guan,*ab Surachai Karnjanakom,a Xiaogang Hao,c Zhongde Wang,c Katsuki Kusakabed and Abuliti Abudulaab

Amphiphobic nanocellulose-modified paper with high durability is successfully fabricated using a facile two-step method. Firstly, nanocellulose-modified paper is prepared through dipping filter paper, i.e., glass microfiber (GM) filter paper and polytetrafluoroethylene (PTFE) filter paper in a dilute nanocellulose dispersed solution. Subsequently, the nanocellulose-coated paper is treated with trichloro(1H,1H,2H,2H- tridecafluoro-n-octyl)silane (FOTS) via chemical vapor deposition. The obtained paper is found to have superhydrophobicity and oleophobicity, repelling both polar and non-polar liquids, on which the drops of water and non-polar liquids with high molecular weight become marble shaped, and the contact angles of water and n-hexadecane reach 156 and 144, respectively. Furthermore, such amphiphobic nanocellulose-modified papers exhibit excellent surface durability in several environments including at various temperatures, and in acid and alkaline solutions, salt solutions and seawater. In addition, such Received 25th November 2015 amphiphobic nanocellulose-modified papers show good repellant properties for several kinds of liquids Accepted 20th January 2016 from our daily life. With outstanding protection to a diverse range of liquids, the amphiphobic DOI: 10.1039/c5ra24986d nanocellulose-modified paper can be applied in the fields of self-cleaning, anti-bacterial, and anti- www.rsc.org/advances corrosion materials.

1 Introduction On the contrary, a solid surface with oil repellent properties is named an oleophobic surface. It is expected that materials can In nature, lotus leaves show self-cleaning properties, on which be developed with an amphiphobic surface, on which both water drops can be removed quickly. This phenomenon water and oil can be repelled quickly. In other words, an inspired us to fabricate similar materials with water repellent amphiphobic surface combines hydrophobicity and oleopho- properties. A simple and quantitative indicator to evaluate the bicity, resulting in a surface with super anti-wetting properties.

Published on 25 January 2016. Downloaded by Taiyuan University of Technology 08/08/2016 04:39:29. tendency of the repelling or wetting properties of a liquid is the This anti-wetting property relates to various advantages such as contact angle of the liquid on the solid surface. A hydrophilic being self-cleaning, anti-bacterial, anti-reective, corrosion solid surface is a surface wetted from water spreading without resistant and so on.8,9 However, the development of such kinds the formation of any droplets or the surface with a water contact of materials is full of more challenges since the lower surface angle of less than 90; in contrast, a hydrophobic solid surface tension of oil generally leads to a higher solid surface attraction – repels the spreading of water generally and has a water contact and as a result oil can easily wet a superhydrophobic surface.8 12 angle higher than 90. Recently, it has been most popular to To fabricate articial superhydrophobic surfaces, two impor- develop a solid surface with superhydrophobicity, on which tant factors, i.e., roughness and surface energy, need to be water apparently forms a droplet, easily slides oﬀ, and the considered. For the surface roughness, Cassie et al.13 addressed formed water droplet has a contact angle of larger than 150.1–7 the wetting theory modelling the wettability of a rough surface. At the small protrusions of a rough surface, it cannot be lled by liquid but can be lled by air, thus only the top areas of a rough aGraduate School of Science and Technology, Hirosaki University, 1-Bunkyocho, surface are wetted by liquid.1,5,6 For the surface energy, liquids Hirosaki 036-8560, Japan with lower surface tension than the critical surface tension of bNorth Japan Research Institute for Sustainable Energy (NJRISE), Hirosaki University, the substrate will wet the surface.2 Generally, superhydrophobic 2-1-3, Matsubara, Aomori 030-0813, Japan. E-mail: [email protected]; Fax: +81- surfaces are extremely low surface energy materials, especially 17-735-5411; Tel: +81-17-762-7756 1 14 cDepartment of Chemical Engineering, Taiyuan University of Technology, Taiyuan lower than the surface tension of water (72.1 mN m ), thus it 030024, China will not be wetted by water. However, to fabricate super- dDepartment of Nanoscience, Sojo University, 4-22-1 Ikeda, Nishi-ku, Kumamoto 860- oleophobic surfaces, other factors which can protect from oil 0082, Japan penetrating the texture should be considered.8,10–12 In addition, † Electronic supplementary information (ESI) available. See DOI: the lower surface tension of oil, i.e., n-hexadecane (27.47 mN 10.1039/c5ra24986d

13328 | RSC Adv.,2016,6, 13328–13334 This journal is © The Royal Society of Chemistry 2016 View Article Online Paper RSC Advances

m 1),14 than water is another challenge for developing the low transform infrared spectroscopy (FTIR) for investigation of the surface tension of superoleophobic surfaces. To fabricate wettability, morphology, and chemical structure of the amphi- superamphiphobic surfaces, a specic combination of low phobic surface. The durability of the amphiphobic surface energy and reentrant surface structure is needed.10–12 Li nanocellulose-modied paper was also tested in various envi- et al.11 developed a method to design and create cellulose-based ronments including at various temperatures, and in acid and natural materials with superamphiphobic properties by alkaline solutions, salt solutions and seawater. In addition, 10 combining the control of cellulose ber size and structure using kinds of liquids from our daily life were used to test its repellant plasma etching and uoropolymer deposition. The obtained properties. It is expected that this will become a facile method handsheets exhibited contact angles of greater than 150 for to fabricate amphiphobic papers with high durability. water, ethylene glycol, motor oil and n-hexadecane. Jin et al.15 also prepared amphiphobic cellulose-based materials using 2 Experimental liquid treatments to generate the necessary roughness, followed 2.1 Materials by self-assembling a 1H,1H,2H,2H-peruorooctyl trimethox- ysilane (PFOTMS) monolayer onto the surface. Nanocellulose from bleached hardwood was provided by Daio Nanocellulose has recently gained great attention from Paper Corporation. GM lter paper (pore size: 1.6 mm; GF/A, researchers and industry because it has some unique properties Whatman) and hydrophilic PTFE lter paper (pore size: 0.1 including high tensile modulus, high specic surface area, mm; H010A047A, Advantec) were used as substrates. FOTS (98%, biodegradability, biocompatibility and sustainability.16,17 Espe- TCI, Japan) was used as received. Sulfuric acid aqueous solution cially, nanocellulose has nanoscale dimensions and is rich in (47 wt%), sodium hydroxide, sodium chloride, n-hexane, n- hydroxyl groups with good aﬃnity to a variety of materials. octane, n-hexadecane, toluene, ethylene glycol, and formamide Thus, it can be applied to make high quality paper with special were purchased from Wako Pure Chemical Ltd. and used surface properties or modify other solid surfaces.18 Using without any further purication. Vacuum pump oil (ultragrade nanocellulose to increase the roughness and reactivity of 15) was purchased from Edwards Ltd. Seawater was collected surfaces is an attractive idea to modify substrates for achieving from Aomori Bay, Aomori City, Japan, and also used for testing amphiphobicity using a natural source. Meanwhile, most without any pretreatment. 19,20 research has used hard particles such as SiO2 particles,  21 22  per uoropolyether (PFPE), and Al2O3 nanoparticles for 2.2 Preparation of nanocellulose-modi ed substrates  surface modi cation to achieve superhydrophobicity and The substrates (GM lter paper and hydrophilic PTFE lter oleophobicity. paper) were cleaned by soaking them in ethanol for 5 h followed To decrease the surface tension of substrates, silane is one by drying them at 110 C for 12 h. Various concentrations (0.01, kind of chemical which interacts with substrates and achieves 0.1 and 0.5 wt%) of nanocellulose dispersions in distilled water amphiphobicity. Silane is a silicon chemical consisting of were prepared at room temperature. A piece of cleaned a hydrolytic center which can react with hydroxyl groups and the substrate was dipped into the well-dispersed nanocellulose 2 long tail of organic substituents. Many kinds of silanes have aqueous solution for 5 h at room temperature. Then, the been used for the generation of amphiphobic surfaces. Jin substrate was taken out from the dispersion solution and dried 23 Published on 25 January 2016. Downloaded by Taiyuan University of Technology 08/08/2016 04:39:29. et al. studied a superamphiphobic aerogel formed through the overnight at 50 C under vacuum. As such, the nanocellulose- chemical vapour deposition of a membrane with various kinds modied papers were obtained. of silane, in which 200 mL of (tridecauoro-1,1,2,2- tetrahydrooctyl) trichlorosilane was used to generate amphi- 2.3 Amphiphobic treatment phobicity. Gonçalves et al.19 studied superhydrophobic cellulose  nanocomposites using two kinds of uorosiloxanes. 500 mLof A piece of nanocellulose-modi ed paper was further treated  with 50 mL of FOTS in a 25 mL bottle, which was sealed with 1H,1H,2H,2H-per uorooctyl triethoxysilane was applied and  a cap and placed in an oven at 90 C for various periods (1–9 h). obtained a water contact angle of 146.8 on their modi ed cellulose ber surface. Even silane is an active chemical for Then, the FOTS-treated paper was stored under vacuum at 50 C producing amphiphobic surfaces, although the environmental overnight for the removal of the unreacted chemical. issues of using it are a concern. Decreasing the amount of silane used in the modication will be a selective way to reduce the 2.4 Characterization harmfulness to nature. Contact angle measurements were carried out using a contact In this study, to obtain amphiphobic papers with high angle meter (DMe-201, Kyowa Interface Science). A 5 mL drop of durability, nanocellulose was used to modify two kinds of lter liquid (water, n-hexane, n-octane, or n-hexadecane) was applied papers, i.e., glass microber (GM) lter paper and hydrophilic on the surface of the substrates. The contact angle was analyzed polytetrauoroethylene (PTFE) lter paper, using a dip coating using FAMAS soware version 3.5.0. All surface contact angle method at rst and then, the nanocellulose-modied paper was values reported here were the average values of at least three treated via chemical vapor deposition with 50 mL of tri- measurements made on diﬀerent positions of the sample chloro(1H,1H,2H,2H-tridecauoro-n-octyl)silane (FOTS). The as- surface. obtained amphiphobic paper was characterized using a contact The surface morphology of the paper was examined using angle meter, scanning electron microscopy (SEM), and Fourier scanning electron microscopy (SEM, SU8010, Hitachi) at an

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acceleration voltage of 1.0 kV. A small piece of paper was xed superhydrophobicity with a water contact angle as large as 156 on carbon tape. Then, the sample was sputter-coated with Pt at and a water droplet on the surface becomes a marble (Fig. 1A 15 mA for 20 seconds to avoid charging. and B). In addition, the nanocellulose concentration has an The chemical composition of the substrate was character- effect on achieving amphiphobicity. Furthermore, its surface ized using Fourier transform infrared spectroscopy (FTIR) also repels the non-polar liquids with high molecular weights, which was recorded by using a Jasco FT/IR-4200 infrared spec- i.e. n-hexadecane and n-octane, and the contact angles reach trophotometer with wavelengths in the range of 500–4000 cm 1. 144 and 118, respectively (Fig. 1C and D). It indicates that the A small piece of the sample was cut and placed between two obtained surface has both superhydrophobicity and near mini-KBr plates, following by pressing into a thin pellet for superoleophobicity in this case. However, it should be noted characterization. that it has no oleophobicity for the non-polar liquids with a low molecular weight such as n-hexane (Fig. 1E). The different 2.5 Durability testing wettability between the low and high molecular weight non- polar liquids comes from the distinctive liquid surface ff To test the e ects of various environments on the amphiphobic tensions at 20 Cofn-hexane, n-octane, and n-hexadecane  properties of FOTS-treated nanocellulose-modi ed paper the which are 18.40, 21.62, and 27.47 mN m 1, respectively.14 Here,  ff selected papers were rstly placed at di erent environmental because the surface energy of the obtained paper has decreased, temperatures ( 30, 9, 30, and 50 C) for 6 h; various concen- it cannot be wetted by water, n-hexadecane, and n-octane. trations of NaCl solutions (1, 3, and 5 wt%) for 6 h at room However, the surface energy is still higher than the liquid ff temperature, various solutions with di erent pH values (1, 3, 5, surface tension of n-hexane, so it can be still wetted by n-hexane. 7, 9, 11, and 14; prepared using 47 wt% sulfuric acid and The contact angles of water, n-hexane, n-octane, and n-hex- sodium hydroxide) for 6 h at room temperature, and seawater in adecane on the FOTS-treated nanocellulose-modied PTFE lter different periods (6, 12, and 24 h) at room temperature, papers with various loading amounts of nanocellulose and respectively. Then, the pretreated papers were dried at 50 C various FOTS treatment periods were also measured. As shown overnight under vacuum for the contact angle measurement. in Table S-1 in the ESI,† the results are similar to those of the  The FOTS-treated nanocellulose-modi ed papers were also FOTS-treated nanocellulose-modied GM lter papers. For the m ff tested by dropping 5 L of ten di erent kinds of liquids directly 0.1 wt% nanocellulose-modied PTFE lter paper, aer it is ff for measuring their contact angles. These ten di erent liquids treated with FOTS for 5 h, its surface also exhibits super- included seawater, sodium chloride solution (5 wt%), distilled hydrophobicity with a water contact angle as large as 153 and ¼ water (7 C), distilled water (50 C), sulfuric acid solution (pH a water droplet on the surface becomes a marble (Fig. S-1A and ¼ 1), sodium hydroxide solution (pH 14), toluene, ethylene B†). However, for the three non-polar liquids, its surface only glycol, formamide, and vacuum pump oil. repels n-hexadecane with a contact angle of 92 (Fig. S-1C†). It indicates that this surface also has superhydrophobicity but only 3 Results and discussion has oleophobicity for some non-polar liquids with a larger molecular weight. For the non-polar liquids with a lower 3.1 Wettability molecular weight, i.e. n-octane and n-hexane, the contact angles †

Published on 25 January 2016. Downloaded by Taiyuan University of Technology 08/08/2016 04:39:29. Table 1 demonstrates the contact angles of water, n-hexane, n- are 43 and 26 , respectively (Fig. S-1D and E ). Herein, it should octane, and n-hexadecane on the FOTS-treated nanocellulose- be noted that the applied GM lter paper has an average pore modied GM lter papers with various loading amounts of diameter of 1.6 mm whereas PTFE lter paper has an average nanocellulose and various FOTS treatment periods, compared pore diameter of 0.1 mm, which could have some effect on their with the untreated samples. One can see that the GM lters amphiphobic properties. In this study, the FOTS-treated without nanocellulose modication and FOTS treatment can be nanocellulose-modied papers with the best amphiphobic wet by water and the other three types of non-polar liquids. This properties were selected for further characterization and testing. is because the GM lter paper is made of borosilicate with a ne capillary structure, which can absorb water and other liquids in fast ow rates for enabling its ltration quality. Moreover, the 3.2 Surface morphology surface energy of unmodied GM lters should be higher than Fig. 2A–C show the morphologies of original GM lter paper, 0.1 the surface tension of water and the other three types of non- wt% nanocellulose-modied GM lter paper and FOTS-treated polar liquids. For the nanocellulose-modied GM lter papers 0.1 wt% nanocellulose-modied GM lter paper, respectively. with various concentrations of nanocellulose but without FOTS One can see that the original GM lter paper is composed of treatment, they also show good affinity to water and the three various straight bers with a smooth surface (Fig. 2A). Aer non-polar liquids since the loaded nanocellulose also has modication with 0.1 wt% nanocellulose, the glass bers are a number of hydroxyl groups, which can create hydrogen bonds found to be signicantly covered with nanocellulose (Fig. S-3A†) with water and organic molecules, making the liquids spread and the surfaces of the bers become rough (Fig. 2B). For the over the surface.1,2 In contrast, for the FOTS-treated papers, the FOTS-treated paper, no signicant difference can be found in wettability is at the level of hydrophobicity and oleophobicity. the morphology (Fig. 2C). However, as shown in the insets of Interestingly, for the 0.1 wt% nanocellulose-modied GM lter Fig. 2, the contact angles of water and n-hexadecane on it have paper, aer it is treated with FOTS for 5 h, its surface exhibits obvious distinctions.

13330 | RSC Adv.,2016,6, 13328–13334 This journal is © The Royal Society of Chemistry 2016 View Article Online Paper RSC Advances

Table 1 Contact angles of various liquids on FOTS treated and untreated nanocellulose-modiﬁed GM ﬁlter papers

Average contact angle ()

Samples Water n-Hexane n-Octane n-Hexadecane

GM lter paper 0 0 0 0 FOTS treated for 1 h 142 0 128 135 FOTS treated for 5 h 145 0 128 138 FOTS treated for 9 h 148 0 117 137

0.01 wt% nanocellulose/GM lter paper 0 0 0 0 FOTS treated for 1 h 151 0 81 134 FOTS treated for 5 h 155 0 93 136 FOTS treated for 9 h 154 0 100 120

0.1 wt% nanocellulose/GM lter paper 0 0 0 0 FOTS treated for 1 h 134 0 53 90 FOTS treated for 5 h 156 0 118 144 FOTS treated for 9 h 154 0 106 140

0.5 wt% nanocellulose/GM lter paper 0 0 0 0 FOTS treated for 1 h 134 0 43 83 FOTS treated for 5 h 139 0 40 58 FOTS treated for 9 h 128 0 74 95

Fig. 1 Liquid droplets on the amphiphobic surface of FOTS treated 0.1

Published on 25 January 2016. Downloaded by Taiyuan University of Technology 08/08/2016 04:39:29. wt% nanocellulose-modiﬁed GM ﬁlter paper. (A) Marble shaped water droplets; (B) water; (C) n-hexadecane; (D) n-octane; (E) n-hexane.

Fig. S-2A–C† show the morphologies of original PTFE lter paper, 0.1 wt% nanocellulose-modied PTFE lter paper and FOTS-treated 0.1 wt% nanocellulose-modied PTFE lter paper, respectively. Compared with GM lter paper, original PTFE lter paper has a denser structure with smaller PTFE bers and lower porosity. Similar to the nanocellulose-modied GM lter paper, for the FOTS-treated nanocellulose-modied PTFE lter paper, no signicant difference can be found in the morphology (Fig. S-2B and C†). However, as shown in the insets of Fig. S-2,† the contact angles of water and n-hexadecane on it have obvious distinctions, and the FOTS-treated nanocellulose-modied PTFE lter paper also shows superhydrophobicity and oleophobicity. In this study, one main advantage of loading nanocellulose on GM lter paper or PTFE lter paper is to increase the roughness of the bers in the lter paper, which is bene- Fig. 2 SEM images of (A) GM filter paper; (B) 0.1 wt% nanocellulose- cial for modifying the wettability of them from hydrophilicity modified GM filter paper; (C) FOTS treated 0.1 wt% nanocellulose- and oleophilicity to superhydrophobicity and oleopho- modified GM filter paper. Insets: contact angles of water and n- hexadecane. bicity.1,3,11,13,15,19,24 Arbatan et al.24 fabricated superhydrophobic

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paper by using cellulose nanobers as a binder to coat precip- itated calcium carbonate on lter paper, followed by treatment with a solution of alkyl ketene dimer in n-heptane, and found that the water contact angle on the obtained paper was much larger than that without using cellulose nanober as a binder. This result is similar to the present study, in which nanocellulose is an eﬀective material for substrate modication. It should be noted that nanocellulose can be solely used for increasing the roughness of the substrate due to its high surface area, which leads to strong adhesion on the bers of the substrate,25 which is positive for amphiphobicity.

3.3 Chemical structure Fig. 3 shows FT-IR spectra of (a) GM lter paper, (b) 0.1 wt% nanocellulose-modied GM lter paper, and (c) FOTS-treated 0.1 wt% nanocellulose-modied GM lter paper. Since the GM lter paper is made of 100% borosilicate glass, its main

chemical composition is silicon dioxide (SiO2), boric oxide 26 (B2O3), and other alkali oxides. In its FT-IR spectrum (Fig. 3-a), the detected peak at 1370 cm 1 is associated with the B–O stretching vibration band while the absorption peak at 1075 cm 1 is the asymmetric stretching vibration of Si–O–Si.27 Aer it is modied using nanocellulose, the absorption peaks at 3500– 3200 and 2894 cm 1 are attributed to the O–H stretching and C–H stretching of nanocellulose, respectively (Fig. S-3B†).28,29 In addition, the appearance of the absorption peak at 1649 cm 1 indicates water absorption by nanocellulose. This result Fig. 3 (A) FT-IR spectra of (a) GM filter paper, (b) 0.1 wt% nano- conrms that the modication using nanocellulose successfully cellulose-modified GM filter paper, and (c) FOTS treated 0.1 wt% increases the amount of O–H on the modied substrate. Aer nanocellulose-modified GM filter paper; (B) enlargement between 1 the FOTS treatment, new absorption peaks are detected at 500–2000 cm . around 1243 and 1143 cm 1 (Fig. 3B-c), which are the C–F 22 stretching and symmetric CF2 stretching of FOTS, respectively. 1 the wavelengths of 1205, and 1150 cm . Based on these FTIR Another new absorption peak at 1072 cm 1 is associated to the results, the possible reaction which occurred on the Si–O–Si asymmetric stretching vibration of FOTS, indicating nanocellulose-modied lter paper should be as shown in – Published on 25 January 2016. Downloaded by Taiyuan University of Technology 08/08/2016 04:39:29. that FOTS has reacted with the OH bonds of nanocellulose.   Fig. 4. The lter paper modi ed with nanocellulose can not only Moreover, the intensity of the O–H group at 3500–3200 cm 1 is increase the roughness of the nanobers, but also increase the also decreased due to less –OH bonds aer the amphiphobic active hydroxyl groups on the paper. With the chemical vapor treatment. This result conrms that the surface of the deposition of FOTS a thin lm composed of covalent linkages as nanocellulose-modied GM lter paper has been successfully shown in Fig. 4 leads to the amphiphobicity of the modied with FOTS, resulting in the improvement of the nanocellulose-modied papers.2,6,21,22,31,32 wettability to superhydrophobicity and oleophobicity. Fig. S-4† shows FT-IR spectra of (a) PTFE lter paper, (b) 0.1 3.4 Durability wt% nanocellulose-modied PTFE lter paper, and (c) FOTS- treated 0.1 wt% nanocellulose-modied PTFE lter paper. As The durability of the amphiphobic surface of the FOTS-treated shown in Fig. S-4a,† the characteristic peaks of PTFE at 1205, 0.1 wt% nanocellulose-modied GM lter paper was evaluated 1 30  1150, and 636 cm indicate stretching of the CF2 group. For by measuring the contact angle a er putting it in various the 0.1 wt% nanocellulose-modied PTFE lter paper, new environments. Fig. 5A shows the contact angles of water and n- peaks at 3500–3200, 2894, and 1649 cm 1 are detected, which hexadecane aer 6 h of soaking in various concentrations of indicate the existence of nanocellulose (Fig. S-4b†). However, for the FOTS-treated 0.1 wt% nanocellulose-modied PTFE lter paper, peaks corresponding to FOTS and Si–O–Si cannot be obviously detected even though the wettability has been improved from hydrophilicity and oleophilicity to amphiphobicity (Fig. S-4c†). This is because the spectral features of new structures such as Si–O–Si from the chemical vapor deposition Fig. 4 Schematic of the chemical vapor deposition of FOTS (R ¼

have been hidden by the main spectral features of PTFE, i.e. at C8H13F4) on the nanocellulose-modiﬁed surface.

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NaCl. The results indicate that the contact angles undergo no Table 2 Contact angles of various liquids on FOTS treated 0.1 wt% fi fi obvious change aer soaking in 1, 3, and 5 wt% NaCl and the nanocellulose-modi ed GM lter paper wettability still remains at the level of superhydrophobic and Average contact ff oleophobic states. Fig. 5B shows the e ect of environmental Liquid angle () temperature on amphiphobicity. One can see that the amphiphobicity is almost unchanged in cold environments, and in Seawater 153 a hot environment (50 C) the contact angles of water and n- Sodium chloride solution (5 wt%) 152 Distilled water (7 C) 150 hexadecane decreased less than 10% but still remain in the Distilled water (50 C) 148 range of amphiphobicity. Fig. 5C shows the durability of the Sulfuric acid solution (pH ¼ 1) 153 amphiphobic surface aer soaking in various solutions with Sodium hydroxide solution (pH ¼ 14) 151 different pH values. One can see that the water contact angles Toluene 136 decrease by around 3% and 7% aer 6 h of soaking in a strong Ethylene glycol 143 Formamide 150 acidic solution (pH ¼ 1) and strong basic solution (pH ¼ 14), Vacuum pump oil 143 respectively, but still remain in the range of ultrahydrophobicity while the contact angle of n-hexadecane decreased by around 3% aer soaking in strong basic solution but still remained in the range of ultraoleophobicity. Fig. 5D shows the stability of the amphiphobic surface soaked in real seawater for 6, 12, and 24 h. One can see that the contact angles aer 24 h of soaking decrease by only around 3% and also remain in the range of amphiphobicity. Fig. S-5† shows the durability of the amphiphobic surface of FOTS-treated 0.1 wt% nanocellulose-modied PTFE lter paper, which was also evaluated by measuring the contact angle aer putting it in the same environments. Almost identical results were obtained. Thus, it can be concluded that the obtained amphiphobic lter papers have excellent durability in various environments. Fig. 6 Various liquid droplets on the amphiphobic surface of FOTS Table 2 and Fig. 6 represent the contact angles of different treated 0.1 wt% nanocellulose-modified GM filter paper. kinds of liquids dropped on the amphiphobic surface of 0.1 wt% nanocellulose-modied GM lter paper. One can see that all contact angles of seawater, sodium chloride solution (5 toluene, ethylene glycol, formamide, and vacuum pump oil are wt%), distilled water (7 C), distilled water (50 C), sulfuric acid higher than 135, indicating that the amphiphobicity is solution (pH ¼ 1), sodium hydroxide solution (pH ¼ 14), retained for different kinds of liquids. Similarly, as shown in Table S-2 and Fig. S-6,† for the amphiphobic surface of 0.1 wt%

Published on 25 January 2016. Downloaded by Taiyuan University of Technology 08/08/2016 04:39:29. nanocellulose-modied PTFE lter paper, except for toluene and vacuum pump oil, the contact angles of the other liquids are larger than 120, also indicating that amphiphobicity can be retained for diﬀerent kinds of liquids.

4 Conclusions

Amphiphobic nanocellulose-modied papers with high durability have been successfully fabricated using a facile two-step method, in which nanocellulose-modied paper can be prepared through dipping lter paper such as GM lter paper and PTFE lter paper in a dilute nanocellulose dispersed solution and then, the nanocellulose-coated paper is further treated with FOTS via chemical vapor deposition. The obtained paper is found to have superhydrophobicity and oleophobicity which can repel various polar and non-polar liquids. Under the Fig. 5 Durability of the contact angles of water and n-hexadecane on optimum conditions, the contact angles of water and n-hex- the amphiphobic surface of FOTS treated 0.1 wt% nanocellulose- fi fi adecane reach 156 and 144 , respectively on the amphiphobic modi ed GM lter paper in various environments. (A) Soaking in   various NaCl solutions for 6 h; (B) various environmental temperatures; surface of 0.1 wt% nanocellulose-modi ed GM lter paper. (C) soaking in various solutions with different pH values; (D) soaking in Furthermore, the obtained amphiphobic nanocellulose- real seawater for different periods. modied papers exhibit high surface durability in several

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