Fabrication of superhydrophobic aromatic cotton fabrics

Abstract

Aromatic silica nanocapsules were fabricated by loading fragrance into hollow mesoporous silica nanoparticles, and coated onto fibers. The obtained fabrics with aromatic nanocapsules were then hydrophobized by a water-repellent finishing agent to fabricate superhydrophobic aromatic fabrics. Scanning electron microscopy was conducted to investigate the morphologies of the nanocapsules and the fabric surfaces. Contact angle measurements of water droplets were conducted to show the wettability of the fabrics. The releasing properties of the silica nanocapsules and the superhydrophobic aromatic fabrics were thoroughly investigated. It was shown that the aromatic silica nanocapsules coated on fibers not only roughened the fabrics, favouring the superhydrophobicity of the substrates, but also imparted the fabrics with long-lasting fragrance due to their sustained-release effect. Importantly, the superhydrophobic property enhanced the sustained releasing performance of fragrance of the aromatic fabrics.

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Introduction

Superhydrophobic surfaces with water contact angles greater than 150° promise a wide range of applications,^1–5 thus they have been extensively studied over the last decade. From a functional point of view, multifunctionalization of superhydrophobic surfaces⁶ is an important way to advance these materials into practical applications, in addition to improving the durability of the superhydrophobicity.^5,7–13 On the one hand, superhydrophobic coatings can be used to improve the performance of conventional materials by surface modification; on the other hand, superhydrophobicity brings about new functions which are not available for the materials themselves.⁶ Additionally, new functions can be added on superhydrophobic surfaces to explore the adaptability of the materials to applications. Until now, many multifunctional superhydrophobic surfaces have been made, such as by incorporating transparent,^14–16 antireflective,^17–19 conductive,^20–24 flame-retardant,^25,26 UV-shielding^27–31 and the other properties onto superhydrophobic materials.

To impart additional functions to superhydrophobic materials, one important way is using functional materials to construct rough structures which are responsible for the superhydrophobicity of surfaces. It was demonstrated that using conductive materials, such as MWCNTs,²¹ graphite,²⁰ mesoporous carbon capsules,²² silver nanoparticles,²⁴ and polyaniline nanowires²³ to construct rough surfaces is very effective to fabricate conductive and superhydrophobic materials. Utilizing the intrinsic flame-retardant nature of the raw melamine materials, a superhydrophobic sponge with excellent flame retardancy was obtained.²⁵ In order to multifunctionalize superhydrophobic surfaces with UV-shielding property, nanomaterials such as TiO₂ nanoparticles,^27,29,31 ZnO nanoparticles/nanorods,^28,30 and CeO₂ nanoparticles³² were used to build roughness before hydrophobization of the materials. Exploring this strategy, researchers can add functions onto superhydrophobic materials according to the requirement of specific application. However, to the best of our knowledge, there are no superhydrophobic surfaces with fragrant property reported.

In this work, superhydrophobic fabrics with lasting lemon fragrance were fabricated in the light of the development trend of high value-added and multi-functional materials. It is recognized that lemon fragrance can not only refresh oneself, relieve tension, eliminate fatigue, and alleviate headaches, but also have multi-function of improving the circulation system, enhancing the immune system, as well as the sterilization and so on. Therefore, the obtained superhydrophobic aromatic fabrics might find great uses in indoor or outdoor applications. In order to obtain sustained-release property of fragrance, we firstly fabricated aromatic silica nanocapsules by loading fragrance into hollow mesoporous silica nanoparticles, utilizing their mechanical robustness, great versatility in surface functionalization, large inner cavity, and low density. Then the aromatic silica nanocapsules were coated onto fibers to make the fabrics aromatic and roughened. At last, the fabrics were hydrophobized with a water-repellent finishing agent to obtain superhydrophobic aromatic fabrics. The fabrication procedures were illustrated in Fig. 1, in which the essential oil can be replaced by fragrances according the requirement of specific applications.

Fig. 1 Illustration of fabrication of superhydrophobic aromatic cotton fabrics.

Experimental

Materials

Styrene, sodium dodecyl benzene sulfonate (SDBS) was purchased from Tianli Chemical Reagent Co., Ltd. Tetraethoxysilane (TEOS), aqueous ammonia (25 wt%), polyvinylpyrrolidone (PVP), hexadecyl trimethyl ammonium bromide (CTAB) were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. 2,2′-Azobis(2-methylpropionamidine) dihydrochloride (AIBA) was purchased from Qingdao Kexin New Materials Science and Technology Co., Ltd. Lemon essential oil (LO) was obtained from Guangzhou Rihua Flavor & Fragrance Co., Ltd. Waterborne polyurethane (WPU) was supplied by Yantai Daocheng Chemicals Co., Ltd. Fluorated water-repellent of AG-950 was purchased from Japan Asahi Glass Co., Ltd. Fatty alcohol polyoxyethylene ether, cotton fabrics and ethanol were commercially obtained. All chemicals were used without further purification.

Preparation of fragrant nanocapsules

Firstly, polystyrene (PS) nanoparticles were synthesized by one-stage emulsion polymerization of styrene according to our previous reports,³³ and used as a template to prepare hollow mesoporous silica nanoparticles (HMSN) as follows:^34,35 1.0 g of CTAB was dissolved in a mixture of 80 mL of water, 40 mL of ethanol. Then, 3 mL of NH₃·H₂O and 20 g of PS solution was added to above mixture, followed by stirring (250 rpm) for 10 min at 35 °C before adding dropwise 1.7 g of TEOS. The hydrolysis and condensation reactions of TEOS were carried out at 35 °C for 6 h under constant stirring to form PS@SiO₂ core@shell particles, which were centrifugated at 12 000 rpm for 5 min, and washed three times with copious amounts of water and ethanol respectively, and then dried at room temperature. After calcinations of the as-prepared PS@SiO₂ particles in air at 550 °C for 2 h, HMSN nanoparticles were obtained.

Then aromatic nanocapsules were prepared as follows:^36,37 0.4 g powder-like as-synthesized HSMN and 20 mL LO, were put into autoclave and sealed. The mixture was stirred at the temperature of 45 °C for 2 hours. The obtained aromatic nanocapsules were isolated by centrifugation, washed extensively with ethanol, and dried at room temperature for use.

Loading capacity and slow-release property of nanocapsules

Loading capacity (LC), which is one of the important parameters during the encapsulation process, was calculated as follows:where W₁ is the weight of the encapsulated lemon essential oil in nanocapsules and W₂ is the weight of nanocapsules.

The weight of the encapsulated lemon essential oil can be calculated indirectly by means of standard curve of lemon essential oil, using UV-visible-near infrared light spectrophotometer to determine the absorbance of the diluted loaded residue at the maximum absorption wavelength (λ_max) of 315 nm. The residue was collected by centrifugation at 12 000 rpm for 3 min, and the precipitate was washed with ethanol. The weight of nanocapsules refers to the weight of the powder after loading by centrifugal washing and freeze drying.

The releasing property of lemon essential oil from aromatic nanocapsules was determined in triplicate. The dried nanocapsules was placed in a culture dish and placed in air environment at different temperatures for a given time. A certain amount of nanocapsules were extracted and filtered at a fixed interval of time. The absorbance of lemon liquid extract was determined by UV-visible-near infrared light spectrophotometer, and the percentage release of lemon essential oil was calculated according to the following formula.

where M₀ is the weight of initial nanocapsule, and M_t is the weight of LO for nanocapsule after placement.

Fabrication of aromatic superhydrophobic cotton fabrics

A certain amount of aromatic nanocapsules (15 g L⁻¹), WPU (100 g L⁻¹), SDBS (2 g L⁻¹), and fatty alcohol polyoxyethylene ether (1 g L⁻¹) was dispersed into water to form a finishing solution using a high speed emulsifying shearing machine. Then cotton fabric samples (6 g, 15 cm × 25 cm) were dipped into 60 g finishing solution for 30 minutes, and nipped by a padder followed by drying at 80 °C for 2 min to obtain aromatic nanocapsule treated fabrics. At last, the above-prepared aromatic fabrics were dip-padded with AG-950 solution with a given concentration, dried at 100 °C, and cured at 150 °C for 3 min to obtain superhydrophobic aromatic fabrics.

Characterization

The morphology of nanoparticles were observed by a field scanning electron microscope (SEM, Hitachi S4800) and a transmission electron microscope (TEM, FEI Tecnai G2 F20 S-TWIN). The surface area was calculated by the Brunauer–Emmett–Teller (BET) method (Micromeritics Instrument Corp ASAP2460). Energy dispersive spectroscopy (EDS, Hitachi S4800) analysis has been performed to examine the chemical elements of the fabric. The loading capacity of lemon essential oil was determined using UV-visible-near infrared light spectrophotometer (Agilent Cary 5000). Determination of functional groups was done by Fourier transform infrared (FT-IR, Bruker VECTOR-22).

The surfaces of fabrics were observed by a field scanning electron microscope (FE-SEM, Hitachi S4800), the static contact angle (CA) of water on the surfaces was measured with a contact angle meter (OCA 20, Dataphysics, Germany). All the CAs and sliding angles (SA) were determined by averaging values measured at six different points on each sample surface.

Result and discussion

Preparation and properties of aromatic nanocapsules

In order to fabricate aromatic nanocapsules, smooth and round PS nanoparticles with an average diameter of approximately 200 nm and perfect monodispersity (Fig. 2(a)) were firstly prepared by emulsion polymerization and coated by SiO₂ through sol–gel process of TEOS in the presence of CTAB surfactants to form PS@SiO₂ core@shell nanoparticles with rough surface as shown in Fig. 2(b). Then PS@SiO₂ nanoparticles were calcinated to remove the template of PS and CTAB, resulting in HMSN nanoparticles, which are round and hollow with a shell thickness of about 33 nm as observed in Fig. 2(c and e). The shell is like having mesoporous structures as reported by previous work.^33,38

Fig. 2 SEM images of (a) PS, (b) PS@SiO₂, (c) HMSN particles, and (d) aromatic capsules; TEM images of (e) HMSN nanoparticle and (f) aromatic capsule.

For further confirmation, specific surface area and porosity measurements were conducted by the Brunauer–Emmett–Teller method. The nitrogen adsorption–desorption isotherms of HSMN (Fig. 3) showed a type IV adsorption behavior and indicated a typical mesoporous material with a pore size of 4.2 nm, a pore volume of 1.56 cm³ g⁻¹, and a BET surface area of 1694.94 m² g⁻¹.

Fig. 3 Nitrogen adsorption–desorption isotherms of HMSN.

Utilizing the hollow and mesoporous structure, HMSN were loaded with fragrance to fabricate aromatic nanocapsules. After adsorption for 2 h, the loading capacity of nanocapsules was up to 85.8%. The high storage capacity may be mainly attributed to their hollow nanostructure and porous shell, where fragrance molecules could be well stored. Beyond that, TEM image of HMSN was conducted after adsorption of essential oil for 2 h (Fig. 2(f)). Compared with the blank HMSN in Fig. 2(e), the aromatic nanocapsules in Fig. 2(f) are spherical after loading fragrance molecules, revealing a good structural stability. However, the surface roughness and the shell thickness obviously changed, and the hollow cavity of the HMSNs changed to be with some shadows. It should be noted that there were not any other materials added in the loading process of LO into HMSN. Therefore, this change might be owing to the interactions of lemon essential oil as well as the formation of aggregates of fragrance molecules by intermolecular forces (e.g. van der Waals, hydrogen bond).^39–42 These results indicated that fragrance was loaded not only on the surface but also into the core of HMSN, which might guarantee the initial as well as the lasting aromatic properties.

Fig. 4 presents the FT-IR spectra of HMSN nanoparticle, aromatic nanocapsule, and lemon essential oil, respectively. In Fig. 4(a), the bands at 807 and 1079 cm⁻¹ are assigned to the symmetrical and asymmetrical vibrations of the bond Si–O–Si. The band at 456 cm⁻¹ is attributed to the bending vibration of the bond Si–O. The spectrum of LO shows several peaks in the Fig. 4(c), in which the band at 2720 cm⁻¹ is the characteristic peaks of citral, the characteristic peak of limonene is 1645 cm⁻¹, and the absorption of C=O stretching vibration is 1730 cm⁻¹. The prominent difference of FT-IR spectrum between lemon essential oil and aromatic nanocapsule is the characteristic Si–O–Si stretching band of HMSN at 1079 cm⁻¹. From these absorption bands, it can be further identified that the lemon essential oil had been successfully loaded into HMSN.

Fig. 4 FT-IR spectra of (a) HMSN particle, (b) aromatic nanocapsules, and (c) lemon essential oil.

The standard curve of lemon essential oil was shown in Fig. 5. The linear regression equation was Y = 0.2434X + 0.0129 (R² = 0.9994), where Y is the absorbance and X is the concentration (in g L⁻¹) of pure lemon essential oil. The maximum loading capacity of the nanocapsules was 85.8% after measurement and calculation.

Fig. 5 Standard curve of lemon essential oil.

The releasing property of lemon essential oil from dried nanocapsules prepared was investigated at different temperatures, with the results shown in Fig. 6. It was found that the amount of the essential oil released was only 7.9% after placed 6 days at temperature of 20 °C. Moreover, essential oil can be released at high temperature of 50 °C for more than 30 hours. The release rate of fragrance of nanocapsules has become increasingly slow as time went on. The results indicated that the aromatic nanocapsules have better sustained-release effect.

Fig. 6 Release properties of LO from nanocapsules at (a) 20 °C, (b) 50 °C.

Aromatic superhydrophobic cotton fabrics

The aromatic property and sustained-release function of the aromatic nanocapsules can be applied to fibers to obtain aromatic fabrics with long-lived fragrance. It was found that, after treatment of fibers with aromatic nanocapsules, the pristine clean cotton fibers with typical longitudinal fibril structure (Fig. 7(a)) were decorated with nanoparticles and their aggregates as shown in Fig. 7(b). And the cotton fabrics became fragrant with lemon essential oil of 8.4% based on the weight of fibers. These nanoparticles as well as the aggregates roughened the fiber surfaces, which might facilitate superhydrophobicity of the fabrics after hydrophobization. SEM images of the aromatic fabrics treated with low surface energy materials of AG-950 of different concentration were shown in Fig. 7(c–h). AG-950 is a commonly used water-repellent containing fluorinated polymers with excellent film-forming property. Fig. 8(a) shows that only of C and O elements are detected on the pristine fabric, and no other impurities can be observed. After treatment with aromatic nanocapsules and AG-950 with concentration of 70 g L⁻¹, additional F and Si elements were observed, as shown in Fig. 8(b). The element Si is from aromatic nanocapsules, and the element of F is from AG-950.

Fig. 7 SEM images of (a) pristine cotton fibers, (b) nanocapsule-treated cotton fibers, and nanocapsule-treated cotton fibers treated by AG-950 of different concentration of (c) 30 g L⁻¹, (d) 40 g L⁻¹, (e) 50 g L⁻¹, (f) 60 g L⁻¹, (g) 70 g L⁻¹, and (h) 80 g L⁻¹.

Fig. 8 EDS spectra of (a) the pristine fabric and (b) the AG-950/nanocapsule-treated fabric.

High temperature curing of AG-950 on the fabrics formed a layer of coating on the surface of fibers. And the coating became thicker with the increase of AG-950 concentration, making enhanced covering of the particles on the fibers from the aromatic nanocapsules, which helped retain the aromatic compounds in the fabrics after hydrophobization, as shown in Fig. 9(a). It was found that the releasing amount of fragrance of AG-950 (70 g L⁻¹)/nanocapsule-treated cotton fabric is much lower than that of the nanocapsule-treated cotton fabric without AG-950 within the same time, as shown in Fig. 9(b). This means that hydrophobization of the fabrics sustained the release of fragrance from the nanocapsules.

Fig. 9 (a) Effect of AG-950 concentration on content of LO of AG-950/nanocapsule-treated fabric; (b) release properties of fragrance from nanocapsule-treated, and AG-950/nanocapsule-treated fabrics.

However, when the concentration of AG-950 reached 80 g L⁻¹, the capsule particles were almost completely covered and layered coatings were found on the fibers. This might hinder the release of fragrance from the nanocapsules affecting the aromatic effect, and decrease the roughness of fibers affecting the superhydrophobicity of the fabrics. Fig. 10 shows that the AG-950/nanocapsule-treated cotton fabrics have excellent water repellent property when the concentration of AG-950 was 70 g L⁻¹.

Fig. 10 Effect of AG-950 concentration on CA and SA of AG-950/nanocapsule-treated cotton fabric.

Fig. 11(a) shows that water can easily spread on the pristine cotton fabric, but formed round drops on the surface of the aromatic fabrics treated with AG-950, showing typical superhydrophobicity with CA up to 165.9°, making water droplets roll easily. When the pristine and AG-950/nanocapsule-treated fabric samples were immersed into dyed water, it was found that the pristine cotton fabric sank into the bottom of the water, while the AG-950/nanocapsule-treated fabric floated on the surface of water (Fig. 11(b)), indicating excellent water repellency. Stability test (Fig. S1–S3†) showed that AG-950/nanocapsule-treated fabric still maintained hydrophobic and aromatic after abrasion of 2000 cycles or laundering of 6 cycles, indicating good durability.

Fig. 11 Dyed water droplets on (a) pristine (top) and AG-950/nanocapsule-treated fabric (bottom), (b) free immersion of pristine and AG-950/nanocapsule-treated fabrics in dyed water.

The AG-950/nanocapsule-treated surface might be favorable to self-cleaning of surfaces. As shown in Fig. 12, the fabric was placed on an inclined plane with a certain slope, and water-soluble Remazol Red dye was used as a model blot and sprayed on pristine cotton fabrics and AG-950/nanocapsule-treated cotton fabric. Then some of the water was dripped onto the dyes of fabric. Fig. 12(a) shows that the pristine cotton fabrics were stained red immediately when the water contacted the substrates due to its hydrophilic property. In contrast, water was dyed red and then took the dye away in water droplets on the AG-950 treated aromatic cotton fabrics. The more the amount of water was used, the more the dye was taken away, and red stains were not found on the surface of fabric. Finally, the surface of the AG-950 treated aromatic cotton fabric became as clean as that before the dye spraying, showing excellent self-cleaning effect.

Fig. 12 Self-cleaning test of (a) pristine fabric, (b) AG-950/nanocapsule-treated fabric.

Conclusions

Superhydrophobic aromatic fabrics were successfully fabricated by roughening fibers with fragrant mesoporous silica nanocapsules followed by hydrophobization with low surface energy film-forming materials. The nanocapsules with the sustained-release property not only impart the fabrics with long-lived fragrance but also increased the roughness of fibers favouring the formation of superhydrophobic surfaces. Additionally, hydrophobization treatment not only makes the aromatic fabrics superhydrophobicity but also prevents the fragrance from fast release, enhancing the sustained release of fragrance. This strategy making aromatic property and superhydrophobicity complementary to each other provides an effective way to obtain multifunctional materials. More importantly, the prepared fabric has good durability.

Acknowledgements

This work was supported by National Natural Science Foundation of China (51372146, 51572161), Research Fund for the Doctoral Program of Higher Education of China (20136125110003), Major Program of Science Foundation of Shaanxi Province (2011ZKC05-7), Key Scientific Research Group of Shaanxi province (2013KCT-08), and Scientific Research Group of Shaanxi University of Science and Technology (TD12-03).

Notes and references

1. L. Wen, Y. Tian and L. Jiang, Angew. Chem., Int. Ed., 2015, 54, 3387–3399.
2. S. Wang, K. Liu, X. Yao and L. Jiang, Chem. Rev., 2015, 115, 8230–8293.
3. S. Nagappan and C.-S. Ha, J. Mater. Chem. A, 2015, 3, 3224–3251.
4. Y. Si and Z. Guo, Nanoscale, 2015, 7, 5922–5946.
5. C.-H. Xue and J.-Z. Ma, J. Mater. Chem. A, 2013, 1, 4146–4161.
6. X. Zhang, F. Shi, J. Niu, Y. Jiang and Z. Wang, J. Mater. Chem., 2008, 18, 621–633.
7. H. Wang, Y. Xue, J. Ding, L. Feng, X. Wang and T. Lin, Angew. Chem., Int. Ed., 2011, 50, 11433–11436.
8. H. Zhou, H. Wang, H. Niu, A. Gestos, X. Wang and T. Lin, Adv. Mater., 2012, 24, 2409–2412.
9. C.-H. Xue, P. Zhang, J.-Z. Ma, P.-T. Ji, Y.-R. Li and S.-T. Jia, Chem. Commun., 2013, 49, 3588–3590.
10. C.-H. Xue, Y.-R. Li, P. Zhang, J.-Z. Ma and S.-T. Jia, ACS Appl. Mater. Interfaces, 2014, 6, 10153–10161.
11. C.-H. Xue, X.-J. Guo, M.-M. Zhang, J.-Z. Ma and S.-T. Jia, J. Mater. Chem. A, 2015, 3, 21797–21804.
12. C.-H. Xue, Y.-R. Li, J.-L. Hou, L. Zhang, J.-Z. Ma and S.-T. Jia, J. Mater. Chem. A, 2015, 3, 10248–10253.
13. C.-H. Xue, X.-J. Guo, J.-Z. Ma and S.-T. Jia, ACS Appl. Mater. Interfaces, 2015, 7, 8251–8259.
14. S. Yu, Z. Guo and W. Liu, Chem. Commun., 2015, 51, 1775–1794.
15. S. Y. Lee, Y. Rahmawan and S. Yang, ACS Appl. Mater. Interfaces, 2015, 7, 24197–24203.
16. N. Yokoi, K. Manabe, M. Tenjimbayashi and S. Shiratori, ACS Appl. Mater. Interfaces, 2015, 7, 4809–4816.
17. A. Yildirim, T. Khudiyev, B. Daglar, H. Budunoglu, A. K. Okyay and M. Bayindir, ACS Appl. Mater. Interfaces, 2013, 5, 853–860.
18. P. Mazumder, Y. Jiang, D. Baker, A. Carrilero, D. Tulli, D. Infante, A. T. Hunt and V. Pruneri, Nano Lett., 2014, 14, 4677–4681.
19. X. Liu, Y. Xu, Z. Chen, K. Ben and Z. Guan, RSC Adv., 2015, 5, 1315–1318.
20. I. S. Bayer, V. Caramia, D. Fragouli, F. Spano, R. Cingolani and A. Athanassiou, J. Mater. Chem., 2012, 22, 2057–2062.
21. H. Yao, C.-C. Chu, H.-J. Sue and R. Nishimura, Carbon, 2013, 53, 366–373.
22. N. Mittal, D. Deva, R. Kumar and A. Sharma, Carbon, 2015, 93, 492–501.
23. M. Qu, G. Zhao, X. Cao and J. Zhang, Langmuir, 2008, 24, 4185–4189.
24. C.-H. Xue, J. Chen, W. Yin, S.-T. Jia and J.-Z. Ma, Appl. Surf. Sci., 2012, 258, 2468–2472.
25. C. Ruan, K. Ai, X. Li and L. Lu, Angew. Chem., Int. Ed., 2014, 53, 5556–5560.
26. H. Cao, H. Zheng, J. Yin, Y. Lu, S. Wu, X. Wu and B. Li, J. Phys. Chem. C, 2010, 114, 17362–17368.
27. W. Taoye, T. I. Tayirjan, C. Jianfeng and R. Sohrab, Nanotechnology, 2011, 22, 265708.
28. C.-H. Xue, W. Yin, S.-T. Jia and J.-Z. Ma, Nanotechnology, 2011, 22, 415603.
29. C.-H. Xue, S.-T. Jia, H.-Z. Chen and M. Wang, Sci. Technol. Adv. Mater., 2008, 9, 035001.
30. C.-H. Xue, W. Yin, P. Zhang, J. Zhang, P.-T. Ji and S.-T. Jia, Colloids Surf., A, 2013, 427, 7–12.
31. J. Y. Huang, S. H. Li, M. Z. Ge, L. N. Wang, T. L. Xing, G. Q. Chen, X. F. Liu, S. S. Al-Deyab, K. Q. Zhang, T. Chen and Y. K. Lai, J. Mater. Chem. A, 2015, 3, 2825–2832.
32. W. Duan, A. Xie, Y. Shen, X. Wang, F. Wang, Y. Zhang and J. Li, Ind. Eng. Chem. Res., 2011, 50, 4441–4445.
33. C.-H. Xue, Z.-D. Zhang, J. Zhang and S.-T. Jia, J. Mater. Chem. A, 2014, 2, 15001–15007.
34. H. Wu, B. Tang and P. Wu, J. Phys. Chem. C, 2012, 116, 2246–2252.
35. N. Kato, T. Ishii and S. Koumoto, Langmuir, 2010, 26, 14334–14344.
36. X. Y. Ming Dong, Y. Y. Li, F. Wei, Y. Zhou, S. L. Zhou and J. H. Zhu, RSC Adv., 2015, 5, 5494–5500.
37. K. Liu, Y. Xu and X. Wang, J. Food Eng., 2012, 110, 390–394.
38. Y. Bao, Y. Yang and J. Ma, J. Colloid Interface Sci., 2013, 407, 155–163.
39. H. Zhang, H. Xu, M. Wu, Y. Zhong, D. Wang and Z. Jiao, J. Mater. Chem. B, 2015, 3, 6480–6489.
40. S. Theisinger, K. Schoeller, B. Osborn, M. Sarkar and K. Landfester, Macromol. Chem. Phys., 2009, 210, 411–420.
41. Y. Zhang, Z. Zhi, T. Jiang, J. Zhang, Z. Wang and S. Wang, J. Controlled Release, 2010, 145, 257–263.
42. J. Hu, Z. B. Xiao, S. S. Ma, R. J. Zhou, M. X. Wang and Z. Li, J. Appl. Polym. Sci., 2012, 123, 3748–3754.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c6ra23558a

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