Self Cleaning
One-Step Modification of Fabrics with Bioinspired Polydopamine@Octadecylamine Nanocapsules for Robust and Healable Self-Cleaning Performance Yanhua Liu, Zhilu Liu, Yupeng Liu, Haiyuan Hu, Yi Li, Pengxun Yan, Bo Yu,* and Feng Zhou*
Self-cleaning fabrics have received much attention in industry and daily life for their advantages that fabrics can be avoided from frequent washing and hence their service life can be extended. Increasing demands for self-cleaning, comfortable and safe textile products prescribes the intensive development of new technologies of textile processing and treatment.[1–3] One of the most intensively developing directions of applying modern achievements in textile industry is the formation of biomimic water repellent fabrics, where dirt is removed by water flux easily. However, applications of these fabrics in practice are limited by the low robustness, since once being mechanically or chemically destroyed they lose their hydrophobic behavior.[4,5] Therefore, improving the robustness of fabrics with water repellency becomes the urgent demand for their practical application.[6,7] Some methods have been developed to obtain textiles with robust liquid repellency such as mechanical and chemical stability. One of the approaches is to create the roughness on the fabric and establish the chemical bonds between the coating and the fabric.[7–11] In order to establish strong adhesion between the coating and the substrates, one approach has been inspired by the adhesive proteins in which 3,4-dihydroxyphenylalanine plays a key role in the attachment to various type of surfaces.[12] The chemistry has also been used to establish robust superhydrophobicity on different substrates.[13–17]
Y. H. Liu, Z. L. Liu, Y. P. Liu, H. Y. Hu, Prof. P. X. Yan, Dr. B. Yu, Prof. F. Zhou State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Sciences Lanzhou 730000, PR China E-mail: [email protected]: [email protected] Y. H. Liu, Prof. P. X. Yan School of Physical Science and Technology Lanzhou University Lanzhou 730000, PR China Dr. Y. Li Institute of Textiles and Clothing The Hong Kong Polytechnic University Hong Kong 649490, PR China DOI: 10.1002/smll.201402383 small 2014, DOI: 10.1002/smll.201402383
Another important method is to introduce the bio-inspired self-healing function into the modified textiles.[1,2,18–21] Selfhealing is of particular interest to improve durability because any textiles, no matter how durable, is susceptible to physical and chemical damages. Several approaches to self-healing liquid repellent textiles have been reported, for example, Tong Lin et al reported a two-step wet-chemistry coating method for durable self-healing superamiphobic surface.[1,18–20] The coated fabrics showed excellent durability to acid, UV light, washing and abrasion. Wu et al prepared an abrasion durable and self-healable superhydrophobic cotton fabric by means of a radiation-induced graft polymerization technique.[21] The water repellency can survive after thousands of abrasion cycles. When the superhydrophobicity is destroyed by mechanical damage, it can be restored by simply stream ironing. Recently, different groups have introduced hydrophobic molecules infused porous surfaces for self-healing omniphobicity.[22–24] Based on this, they prepared SLIPS-functionalized cotton and polyester fabrics which exhibited pressure tolerance and mechanical robustness.[2] However, most of the works on self-healing coatings with extreme wetting properties used fluoro-containing agents which are harmful to environment and human body, and the preparation process also is complicated. Thus, it would be desirable to facile create liquid repellent coatings with self-healing ability, robustness and non-toxicity, which is believed to be an efficient and longdesired way to solve the problem of poor durability caused by physical and chemical damages. Herein, we report that one step approach to prepare self-healing hydrophobic fabrics without using any fluoro-containing compounds. The approach uses polydopamine@octadecylamine (PDA@ODA) nanocapsules to modify fabrics, where PDA nanocapsule is used as a container for storing ODA with low-surface-energy. The PDA@ODA nanocapsules were spontaneously deposited from a microemulsion of octadecylamine and dopamine onto fabrics with high adhesion strength and provided roughness to complement the microscale roughness inherent in the fabric weaves for hydrophobicity. When the coated fabric is destroyed by physical and chemical damages and lose its liquid repellency, ODA molecules can migrate to the surface and restore the liquid repellency.
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Figure 1. (a) Schematic illustration of chemical structures and coating procedure for the fabrication of hydrophobic fabric, (b) photo of fabric before (blue) and after (brown) coating treatment, (c) liquid droplets on PDA@ODA nanocapsules coated fabric.
The chemical structure of materials used for the coating solutions and the process of fabric treatment are shown in Figure 1. PDA@ODA nanocapsules were used as coating materials and applied onto the fabric substrate using a simple in-situ polymerization method. After coating treatment, the fabric turned to brown, as depicted in Figure 1b. As illustrated in Figure 1c, the modified fabric showed a considerable increase in its liquid repellency. The water, juice, coffee and milk droplets (10 µL) form round balls on the treated fabric with a contact angle (CA) of 145°, 140°, 138°, 142°, respectively. Though the contact angles don’t show a lotus effect (CA > 150°), these liquid droplets don’t pin on surface and have very low sliding angle of less than 10°. Thus, the textile exhibited very good anti-contamination property. To demonstrate the self-cleaning behaviors of the modified fabric, both liquids and solid contamination were tested. As an example of liquid contamination, as shown in Figure S1 in supplementary materials, gloves modified with PDA@ODA nanocapsules shows strong anti-contamination property even when being soaked in juice and cola. Not any stain was left on modified gloves, while untreated gloves were hydrophilic and liable to be stained. For solid contamination, a thick layer of dust particles as a solid contamination example was spread on the modified surface, as described in Figure S2. With a flux of water running across the fabric, the dust particles can be easily removed from the surface. After rolling off from the surface, dust particles can be removed from the fabric while
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the fabric still remain dry, as shown in Figure S2c. On the surface of uncoated fabric, dust particles could not be removed with the water flow, conversely, they still stick to the surface (Figure S2d). Figure 2 provides the morphological information of the fabric before and after the coating treatment. Without coating, the fibers showed a smooth surface (Figure 2a,c). The coated fibers were much rougher (Figure 2b,d), which provides roughness at the nanoscale to compliment the microscale roughness inherent in the fabric weave. The roughness is resulted from the formed PDA@ODA nanocapsules, as seen in Figure 2d clearly. The inset transmission electron microscope (TEM) image proves the nanoparticle coated on fiber is PDA@ODA nanocapsule. The chemical components of the coating layer were verified by Fourier-transform infrared spectroscopy (FTIR), as illustrated in Figure 2e. After coating modification, the vibration peak appeared at 1645 cm−1, which was assigned to the C=N stretching vibrations of Schiff base reaction product between PDA and ODA.[17] The peaks appeared at 2922 and 2856 cm−1 were attributed to C–H stretching vibrations of methylene. The FTIR results confirmed that the fabric was covered with PDA@ODA nanocapsules with alkyl chain on the surface. To demonstrate the self-healing ability, the coated fabric was destroyed by plasma treatment using oxygen as gas source. After the treatment, the surface became hydrophilic with a contact angle of 0° to water, juice, coffee and milk
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small 2014, DOI: 10.1002/smll.201402383
One-Step Modification of Fabrics for Robust Self-Cleaning
Figure 2. Scanning electron microscope (SEM) images of (a,c) uncoated and (b,d) PDA@ODA coated fabrics, the inset shows a TEM image of PDA@ODA nanocapsule, in which the scale is 20 nm, (e) FTIR spectra of uncoated, coated fabrics and PDA@ODA nanocapsules.
(Figure 3a). However, When the fabric treated by plasma was heated at 80 °C for 20 min, its liquid-repellency was restored (Figure 3c). Under SEM, the coated fabric after 20 times plasma treatment still remained the micro- and nano-scale
hierarchical structure though the fiber surface became more rougher (Figure 3b). After healing by heat treatment, seen from Figure 3d, the fiber morphology is uniform with welldistributed nanocapsules as before. This self-healing ability
Figure 3. Photos of liquid droplets on fabrics (a) after plasma treatment and (c) after plasma and heat treatment, SEM images of fabrics (b) after plasma treatment and (d) after plasma and heat treatment, (e) contact angles of water, juice, coffee, and milk on the coated fabric in the ten cycles of plasma and heat treatment. (f) Schematic and data of dyeing and self-healing of dyed fabric. small 2014, DOI: 10.1002/smll.201402383
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was repeatable and worked for 10 times. Figure 3e shows the change of CA in ten cycles of plasma and heat treatments. It is interesting to note that the treated fabric can repair its liquid-repellency easily. The heat induced self-healing property makes fabrics’s hydrophobicity be repaired in each heating process. As shown in Figure S3 (Supporting Information), after plasma treatment, the peak at 1645 cm−1 corresponded to C=N reduced considerably, and peaks intensity at 2922 and 2856 cm−1 attributed to C–H stretching vibrations of methylene also decreased. When the plasma treated fabric was heated at 80 °C for 20 min, the peak at 1645 cm−1 increased, and the peaks at 2922 and 2856 cm−1 were also increased. These results indicate that plasma treatment breaks C=N bonds between PDA and ODA, and hence alkyl chains also were detached from the coated layer, while heat treatment leads to the release of ODA molecules from the capsules and reintroduces alkyl chains for the fabric surface. The color change due to deposition of PDA is undesirable in textile industry. It is very important to investigate whether the treated fabric could be further dyed and whether dyeing would affect the self-healing property. As shown in Figure 3f, the self-healed textile was treated with oxygen plasma and was subsequently dyed with different dyes. The brown color of modified fabrics can be changed to acceptable colors for textiles after dyeing with rose red, orange, and blue colors. Interestingly, the dyed fabric still remains self-healing property, the mechanism is shown in the scheme of Figure 3f. This makes the technology promising for real application. On critical issue for fabric modification is that the modified materials must withstand laundering. Laundering durability of the coated fabric was evaluated in blank water and in soap solution by machine and hand washing. As shown in Figure 4a, after being treated in water after 20 cycles of home machine laundry, the coated fabric still maintained its liquid-repellency though the CA underwent a slight change with the increasing washing cycles. Figure 4b depicts that the
hydrophobicity of the coated fabric decreased slightly after washing, but the hydrophobicity restored with the CA of 144° when it was heated at 80 °C for 20 min. After washing 20 cycles, the PDA@ODA nanocapsules can be clearly observed on the coating surface (Figure 4c,d), indicating that the nanocapsules were immobilized firmly on the fiber surface. In order to further test the washing durability of the coated fabric, it was washed 5 minutes by hand in an aqueous solution containing soap powders. As shown in Figure 4e, after hand-laundering, the coated fabric still remains its hydrophobicity, and liquid droplets can roll off easily from the surface (Figure 4f), which verified that the fabric coated with PDA@ODA capsules has good washing durability both in pure water and in soap solution. The change in liquid repellency with abrasion cycles is presented in Figure 5a. With the increase of abrasion cycles, the contact angle of water, juice and coffee decreased slightly. It was very interesting to note that the abrasion-induced degradation in liquid repellency was repairable. As shown in Figure 5b, once heat treatment was performed on the fabric after abrasion, the hydrophobicity of the fabric was retained. Under SEM (Figure 5c and d), the morphologies of the fabric after abrasion almost have no change, remaining rough structure coated with PDA@ODA nanocapsules. According to these results, the self-healing mechanism of PDA@ODA capsules modified fabric was proposed. When the coating was damaged by plasma treatment, alkyl chains on the surface was destroyed, and then PDA layer exposured, leading to reduced hydrophobicity because of the increased surface free energy. When the plasma treated fabric was heated at 80 °C, some amount of ODA in PDA@ODA capsules melted and became to liquid due to its low fusion point (50–54 °C), which leaded to release of ODA. ODA molecules will migrate from the inside of PDA@ODA capsules to the surface of PDA@ODA capsules. As a result, the surface energy decreased considerably, resulting in recovery of liquid repellency.
Figure 4. (a) CA change with washing cycles, the inset is the photo of liquid droplets on coated fabric after washing 20 cycles, (b) water contact angle change after washing and heat treatment, (c, d) SEM images of the coated fabric after (c) 20 cycles washing and (d) heat treatment. Photos of liquid droplets on the coated fabric after hand-laundering using soap solution (e) and the surface of coated fabric after liquid droplets rolled off (f).
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small 2014, DOI: 10.1002/smll.201402383
One-Step Modification of Fabrics for Robust Self-Cleaning
Figure 5. (a) CA change with abrasion cycles, (b) water contact angle before and after heat treatment for every 100 abrasion cycles, inserted images: the images of water droplets on the fabric before and after an abrasion test of 500 cycles and after heat treatment, (c, d) SEM images of the coated fabric after 500 cycles abrasion.
In conclusion, a facile in-situ polymerization method has been developed to coat fabrics with polydopamine@octadecylamine and hence endows the fabrics with self-cleaning and multi-self-healing ability. The treated fabric is also durable to withstand washing and mechanical abrasion without apparently changing the hydrophobicity. Moreover, the fabric has self-healing ability after surface damage with oxygen plasma. Such a durable and hydrophobic fabric with self-healing ability may be useful for various applications in self-cleaning protection in our everyday life. Thanks to the versatile adhesive property of polydopamine on virtually any substrates, the approach shows very good compability with a variety of substrate materials, such as different types of fabrics, glass, sponge, paper, polymeric materials (see supplementary materials Figure S4-S8).
Experimental Section Materials: Dopamine was purchased from Acros Organic. Octadecylamine (ODA) and tris (hydroxymethyl) aminomethane (Tris) were obtained from Shanghai Chemical Regent Co. Fabrics are commercially available polyester fabric (double-faced pile). Methods: Firstly, ODA was added in deionized water by supersonic stirring to form an ivory-white emulsion. Then, ODA emulsion was dispersed in Tris-HCl (pH = 8.5) buffer with 0.5 mg/mL dopamine and a piece of clean fabric was soaked to the as-prepared mixture for 24 h at ambient temperature. Finally, the resulting brown textile was washed with ethanol and deionized water to remove the residuals, and then dried at room temperature for 12 h. Plasma Treatment: The sample was subjected to an oxygen plasma treatment using a plasma machine (Diener Electronic, small 2014, DOI: 10.1002/smll.201402383
Germany) for each 30 s plasma treatment. Such a plasma treatment can make the sample completely hydrophilic (contact angle: 0°). The plasma treated fabric was heated at 80 °C for 20 min. Then contact angle was measured again after self-healing. Washing Durability: The washing durability was evaluated using a laundering machine (Haier Co., Ltd, Qingdao, China). The fabric sample was laundered in 12 L water and with standard washing mode at 25 °C. After 45 min laundering, the sample was taken out and dried at room temperature, then the contact angle was measured. Healing was performed by heating the damaged sample at 80 °C for 20 min. Then, contact angle was measured again after self-healing. Abrasion Test: The abrasion durability was tested using a dry crocking method according to the GB/T 3920–2008 standard. The fabric sample was fixed on a dynamic disk which was brought into contact with an abradant superjacent. Uncoated fabric was used as abradant, and the abradant was fixed on a separate motionless disk. A loading pressure of 10 kPa was employed. During the test, the dynamic disk moved to and fro, in which the movement rate was 200 mm/min and the reciprocate stroke was 40 mm. Dyeing Method: In order to prettify the fabric modified with PDA@ODA nanocapsules, the fabric was dyed with rose red, orange, and blue colors. The coated cotton fabric was treated using oxygen plasma and then dipped in three kinds of dyebaths respectively (1% azaleine solution, 1% methyl orange solution, and 1% methylene blue solution) for 10 min. The unfixed dye was removed by water rinsing and then the dyed fabric was dried in oven at 80 °C for 20 min. Characterization: Sessile water-droplet contact angle (CA) values were acquired using a DSA-100 optical contact-angle meter (Kruss Co., Ltd., Germany) at ambient temperature. A 10 µL amount of deionized water, juice, coffee, milk were respectively dropped
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onto the samples using an automatic dispense controller, and the CAs were determined automatically using the Laplace-Young fitting algorithm. Average CA values were obtained by measuring the sample at five different positions, and images were captured with a digital camera (Sony, Ltd., Japan). SEM images were obtained on a JSM-6701F field emission scanning electron microscope (FESEM, Japan) at 5–10 kV, and TEM images were obtained on a FEI Tecnai G2 F30 transmission electronic microscope. Fourier transform infrared (FT-IR) spectroscopy was performed to investigate the characteristics of the specimens with KBr pellets on a Nicolet is 10 instrument (Thermo Scientific). All the photos were taken using a Canon camera.
Supporting Information Supporting Information is available from the Wiley Online Library or from the author.
Acknowledgements This research project was financially supported by the National Natural Science Foundation of China (51203173, 21303233 and 51335010). [1] H. X. Wang, H. Zhou, A. Gestos, J. F. Fang, H. T. Niu, J. Ding, T. Lin, Soft Matter 2013, 9, 277–282. [2] C. Shillingford, N. MacCallum, T. S. Wong, P. Kim, J. Aizenberg, Nanotechnology 2014, 25, 014019. [3] C. H. Xue, J. Z. Ma, J. Mater. Chem. A. 2013, 1, 4146–4161. [4] S. Li, S. Zhang, X. Wang, Langmuir 2008, 24, 5585– 5590.
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[5] R. Dastjerdi, M. Montazer, S. Shahsavan, Colloid Surface B 2010, 81, 32–41. [6] T. Verho, C. Bower, P. Andrew, S. Franssila, O. Ikkala, R. H. A. Ras, Adv. Mater. 2011, 23, 673–678. [7] B. Deng, R. Cai, Y. Yu, H. Q. Jiang, C. L. Wang, J. Li, L. F. Li, M. Yu, J. Y. Li, L. D. Xie, Q. Huang, C. H. Fan, Adv. Mater. 2010, 22, 5473–5477. [8] J. Zimmermann, F. A. Reifler, G. Fortunato, L. C. Gerhardt, S. Seeger, Adv. Funct. Mater. 2008, 18, 3662–3669. [9] H. Zhou, H. X. Wang, H. T. Niu, A. Gestos, X. G. Wang, T. Lin, Adv. Mater. 2012, 24, 2409–2412. [10] C. H. Xue, P. Zhang, J. Z. Ma, P. T. Ji, Y. R. Li, S. T. Jia, Chem. Commun. 2013, 49, 3588–3590. [11] M. E. Yazdanshenas, M. Shateri-Khalilabad, Ind. Eng. Chem. Res. 2013, 52, 12846–12854. [12] H. Lee, S. M. Dellatore, W. M. Miller, P. B. Messersmith, Science 2007, 318, 426–430. [13] L. Zhang, J. J. Wu, Y. X. Wang, Y. H. Long, N. Zhao, J. Xu, J. Am. Chem. Soc. 2012, 134, 9879–9881. [14] Y. Liao, R. Wang, A. G. Fane, J. Membrane Sci. 2013, 440, 77–87. [15] I. You, Y. C. Seo, H. Lee, RSC Adv. 2014, 4, 10330–10333. [16] J. L. Wang, K. F. Ren, H. Chang, S. M. Zhang, L. J. Jin, J. Jian, Phys. Chem. Chem. Phys. 2014, 16, 2936–2943. [17] Q. Zhu, Q. M. Pan, ACS Nano 2014, 8, 1402–1409. [18] H. X. Wang, Y. H. Xue, J. Ding, L. F. Feng, X. G. Wang, T. Lin, Angew. Chem. Int. Ed. 2011, 50, 11433–11436. [19] H. Zhou, H. X. Wang, H. T. Niu, A. Gestos, T. Lin, Adv. Funct. Mater. 2013, 23, 1664–1670. [20] H. X. Wang, H. Zhou, A. Gestos, J. Fang, T. Lin, ACS Appl. Mater. Inter. 2013, 5, 10221–10226. [21] J. X. Wu, J. Y. Li, B. Deng, H. Q. Jiang, Z. Q. Wang, M. Yu, L. F. Li, C. Y. Xing, Y. J. Li, Sci. Rep. 2013, 3, 2951. [22] X. L. Wang, X. J. Liu, F. Zhou, W. M. Liu, Chem. Commun. 2011, 47, 2324–2326. [23] Y. Li, L. Li, J. Q. Sun, Angew. Chem. Int. Ed. 2010, 49, 6129–6133. [24] T. S. Wong, S. H. Kang, S. K. Y Tang, E. J. Smythe, B. D. Hatton, A. Grinthal, J. Aizenberg, Nature 2011, 477, 443–447.
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Received: August 9, 2014 Published online:
small 2014, DOI: 10.1002/smll.201402383
One-Step Modification of Fabrics with Bioinspired Polydopamine@Octadecylamine Nanocapsules for Robust and Healable Self-Cleaning Performance Yanhua Liu, Zhilu Liu, Yupeng Liu, Haiyuan Hu, Yi Li, Pengxun Yan, Bo Yu,* and Feng Zhou*
Self-cleaning fabrics have received much attention in industry and daily life for their advantages that fabrics can be avoided from frequent washing and hence their service life can be extended. Increasing demands for self-cleaning, comfortable and safe textile products prescribes the intensive development of new technologies of textile processing and treatment.[1–3] One of the most intensively developing directions of applying modern achievements in textile industry is the formation of biomimic water repellent fabrics, where dirt is removed by water flux easily. However, applications of these fabrics in practice are limited by the low robustness, since once being mechanically or chemically destroyed they lose their hydrophobic behavior.[4,5] Therefore, improving the robustness of fabrics with water repellency becomes the urgent demand for their practical application.[6,7] Some methods have been developed to obtain textiles with robust liquid repellency such as mechanical and chemical stability. One of the approaches is to create the roughness on the fabric and establish the chemical bonds between the coating and the fabric.[7–11] In order to establish strong adhesion between the coating and the substrates, one approach has been inspired by the adhesive proteins in which 3,4-dihydroxyphenylalanine plays a key role in the attachment to various type of surfaces.[12] The chemistry has also been used to establish robust superhydrophobicity on different substrates.[13–17]
Y. H. Liu, Z. L. Liu, Y. P. Liu, H. Y. Hu, Prof. P. X. Yan, Dr. B. Yu, Prof. F. Zhou State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical Physics Chinese Academy of Sciences Lanzhou 730000, PR China E-mail: [email protected]: [email protected] Y. H. Liu, Prof. P. X. Yan School of Physical Science and Technology Lanzhou University Lanzhou 730000, PR China Dr. Y. Li Institute of Textiles and Clothing The Hong Kong Polytechnic University Hong Kong 649490, PR China DOI: 10.1002/smll.201402383 small 2014, DOI: 10.1002/smll.201402383
Another important method is to introduce the bio-inspired self-healing function into the modified textiles.[1,2,18–21] Selfhealing is of particular interest to improve durability because any textiles, no matter how durable, is susceptible to physical and chemical damages. Several approaches to self-healing liquid repellent textiles have been reported, for example, Tong Lin et al reported a two-step wet-chemistry coating method for durable self-healing superamiphobic surface.[1,18–20] The coated fabrics showed excellent durability to acid, UV light, washing and abrasion. Wu et al prepared an abrasion durable and self-healable superhydrophobic cotton fabric by means of a radiation-induced graft polymerization technique.[21] The water repellency can survive after thousands of abrasion cycles. When the superhydrophobicity is destroyed by mechanical damage, it can be restored by simply stream ironing. Recently, different groups have introduced hydrophobic molecules infused porous surfaces for self-healing omniphobicity.[22–24] Based on this, they prepared SLIPS-functionalized cotton and polyester fabrics which exhibited pressure tolerance and mechanical robustness.[2] However, most of the works on self-healing coatings with extreme wetting properties used fluoro-containing agents which are harmful to environment and human body, and the preparation process also is complicated. Thus, it would be desirable to facile create liquid repellent coatings with self-healing ability, robustness and non-toxicity, which is believed to be an efficient and longdesired way to solve the problem of poor durability caused by physical and chemical damages. Herein, we report that one step approach to prepare self-healing hydrophobic fabrics without using any fluoro-containing compounds. The approach uses polydopamine@octadecylamine (PDA@ODA) nanocapsules to modify fabrics, where PDA nanocapsule is used as a container for storing ODA with low-surface-energy. The PDA@ODA nanocapsules were spontaneously deposited from a microemulsion of octadecylamine and dopamine onto fabrics with high adhesion strength and provided roughness to complement the microscale roughness inherent in the fabric weaves for hydrophobicity. When the coated fabric is destroyed by physical and chemical damages and lose its liquid repellency, ODA molecules can migrate to the surface and restore the liquid repellency.
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Figure 1. (a) Schematic illustration of chemical structures and coating procedure for the fabrication of hydrophobic fabric, (b) photo of fabric before (blue) and after (brown) coating treatment, (c) liquid droplets on PDA@ODA nanocapsules coated fabric.
The chemical structure of materials used for the coating solutions and the process of fabric treatment are shown in Figure 1. PDA@ODA nanocapsules were used as coating materials and applied onto the fabric substrate using a simple in-situ polymerization method. After coating treatment, the fabric turned to brown, as depicted in Figure 1b. As illustrated in Figure 1c, the modified fabric showed a considerable increase in its liquid repellency. The water, juice, coffee and milk droplets (10 µL) form round balls on the treated fabric with a contact angle (CA) of 145°, 140°, 138°, 142°, respectively. Though the contact angles don’t show a lotus effect (CA > 150°), these liquid droplets don’t pin on surface and have very low sliding angle of less than 10°. Thus, the textile exhibited very good anti-contamination property. To demonstrate the self-cleaning behaviors of the modified fabric, both liquids and solid contamination were tested. As an example of liquid contamination, as shown in Figure S1 in supplementary materials, gloves modified with PDA@ODA nanocapsules shows strong anti-contamination property even when being soaked in juice and cola. Not any stain was left on modified gloves, while untreated gloves were hydrophilic and liable to be stained. For solid contamination, a thick layer of dust particles as a solid contamination example was spread on the modified surface, as described in Figure S2. With a flux of water running across the fabric, the dust particles can be easily removed from the surface. After rolling off from the surface, dust particles can be removed from the fabric while
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the fabric still remain dry, as shown in Figure S2c. On the surface of uncoated fabric, dust particles could not be removed with the water flow, conversely, they still stick to the surface (Figure S2d). Figure 2 provides the morphological information of the fabric before and after the coating treatment. Without coating, the fibers showed a smooth surface (Figure 2a,c). The coated fibers were much rougher (Figure 2b,d), which provides roughness at the nanoscale to compliment the microscale roughness inherent in the fabric weave. The roughness is resulted from the formed PDA@ODA nanocapsules, as seen in Figure 2d clearly. The inset transmission electron microscope (TEM) image proves the nanoparticle coated on fiber is PDA@ODA nanocapsule. The chemical components of the coating layer were verified by Fourier-transform infrared spectroscopy (FTIR), as illustrated in Figure 2e. After coating modification, the vibration peak appeared at 1645 cm−1, which was assigned to the C=N stretching vibrations of Schiff base reaction product between PDA and ODA.[17] The peaks appeared at 2922 and 2856 cm−1 were attributed to C–H stretching vibrations of methylene. The FTIR results confirmed that the fabric was covered with PDA@ODA nanocapsules with alkyl chain on the surface. To demonstrate the self-healing ability, the coated fabric was destroyed by plasma treatment using oxygen as gas source. After the treatment, the surface became hydrophilic with a contact angle of 0° to water, juice, coffee and milk
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small 2014, DOI: 10.1002/smll.201402383
One-Step Modification of Fabrics for Robust Self-Cleaning
Figure 2. Scanning electron microscope (SEM) images of (a,c) uncoated and (b,d) PDA@ODA coated fabrics, the inset shows a TEM image of PDA@ODA nanocapsule, in which the scale is 20 nm, (e) FTIR spectra of uncoated, coated fabrics and PDA@ODA nanocapsules.
(Figure 3a). However, When the fabric treated by plasma was heated at 80 °C for 20 min, its liquid-repellency was restored (Figure 3c). Under SEM, the coated fabric after 20 times plasma treatment still remained the micro- and nano-scale
hierarchical structure though the fiber surface became more rougher (Figure 3b). After healing by heat treatment, seen from Figure 3d, the fiber morphology is uniform with welldistributed nanocapsules as before. This self-healing ability
Figure 3. Photos of liquid droplets on fabrics (a) after plasma treatment and (c) after plasma and heat treatment, SEM images of fabrics (b) after plasma treatment and (d) after plasma and heat treatment, (e) contact angles of water, juice, coffee, and milk on the coated fabric in the ten cycles of plasma and heat treatment. (f) Schematic and data of dyeing and self-healing of dyed fabric. small 2014, DOI: 10.1002/smll.201402383
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was repeatable and worked for 10 times. Figure 3e shows the change of CA in ten cycles of plasma and heat treatments. It is interesting to note that the treated fabric can repair its liquid-repellency easily. The heat induced self-healing property makes fabrics’s hydrophobicity be repaired in each heating process. As shown in Figure S3 (Supporting Information), after plasma treatment, the peak at 1645 cm−1 corresponded to C=N reduced considerably, and peaks intensity at 2922 and 2856 cm−1 attributed to C–H stretching vibrations of methylene also decreased. When the plasma treated fabric was heated at 80 °C for 20 min, the peak at 1645 cm−1 increased, and the peaks at 2922 and 2856 cm−1 were also increased. These results indicate that plasma treatment breaks C=N bonds between PDA and ODA, and hence alkyl chains also were detached from the coated layer, while heat treatment leads to the release of ODA molecules from the capsules and reintroduces alkyl chains for the fabric surface. The color change due to deposition of PDA is undesirable in textile industry. It is very important to investigate whether the treated fabric could be further dyed and whether dyeing would affect the self-healing property. As shown in Figure 3f, the self-healed textile was treated with oxygen plasma and was subsequently dyed with different dyes. The brown color of modified fabrics can be changed to acceptable colors for textiles after dyeing with rose red, orange, and blue colors. Interestingly, the dyed fabric still remains self-healing property, the mechanism is shown in the scheme of Figure 3f. This makes the technology promising for real application. On critical issue for fabric modification is that the modified materials must withstand laundering. Laundering durability of the coated fabric was evaluated in blank water and in soap solution by machine and hand washing. As shown in Figure 4a, after being treated in water after 20 cycles of home machine laundry, the coated fabric still maintained its liquid-repellency though the CA underwent a slight change with the increasing washing cycles. Figure 4b depicts that the
hydrophobicity of the coated fabric decreased slightly after washing, but the hydrophobicity restored with the CA of 144° when it was heated at 80 °C for 20 min. After washing 20 cycles, the PDA@ODA nanocapsules can be clearly observed on the coating surface (Figure 4c,d), indicating that the nanocapsules were immobilized firmly on the fiber surface. In order to further test the washing durability of the coated fabric, it was washed 5 minutes by hand in an aqueous solution containing soap powders. As shown in Figure 4e, after hand-laundering, the coated fabric still remains its hydrophobicity, and liquid droplets can roll off easily from the surface (Figure 4f), which verified that the fabric coated with PDA@ODA capsules has good washing durability both in pure water and in soap solution. The change in liquid repellency with abrasion cycles is presented in Figure 5a. With the increase of abrasion cycles, the contact angle of water, juice and coffee decreased slightly. It was very interesting to note that the abrasion-induced degradation in liquid repellency was repairable. As shown in Figure 5b, once heat treatment was performed on the fabric after abrasion, the hydrophobicity of the fabric was retained. Under SEM (Figure 5c and d), the morphologies of the fabric after abrasion almost have no change, remaining rough structure coated with PDA@ODA nanocapsules. According to these results, the self-healing mechanism of PDA@ODA capsules modified fabric was proposed. When the coating was damaged by plasma treatment, alkyl chains on the surface was destroyed, and then PDA layer exposured, leading to reduced hydrophobicity because of the increased surface free energy. When the plasma treated fabric was heated at 80 °C, some amount of ODA in PDA@ODA capsules melted and became to liquid due to its low fusion point (50–54 °C), which leaded to release of ODA. ODA molecules will migrate from the inside of PDA@ODA capsules to the surface of PDA@ODA capsules. As a result, the surface energy decreased considerably, resulting in recovery of liquid repellency.
Figure 4. (a) CA change with washing cycles, the inset is the photo of liquid droplets on coated fabric after washing 20 cycles, (b) water contact angle change after washing and heat treatment, (c, d) SEM images of the coated fabric after (c) 20 cycles washing and (d) heat treatment. Photos of liquid droplets on the coated fabric after hand-laundering using soap solution (e) and the surface of coated fabric after liquid droplets rolled off (f).
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One-Step Modification of Fabrics for Robust Self-Cleaning
Figure 5. (a) CA change with abrasion cycles, (b) water contact angle before and after heat treatment for every 100 abrasion cycles, inserted images: the images of water droplets on the fabric before and after an abrasion test of 500 cycles and after heat treatment, (c, d) SEM images of the coated fabric after 500 cycles abrasion.
In conclusion, a facile in-situ polymerization method has been developed to coat fabrics with polydopamine@octadecylamine and hence endows the fabrics with self-cleaning and multi-self-healing ability. The treated fabric is also durable to withstand washing and mechanical abrasion without apparently changing the hydrophobicity. Moreover, the fabric has self-healing ability after surface damage with oxygen plasma. Such a durable and hydrophobic fabric with self-healing ability may be useful for various applications in self-cleaning protection in our everyday life. Thanks to the versatile adhesive property of polydopamine on virtually any substrates, the approach shows very good compability with a variety of substrate materials, such as different types of fabrics, glass, sponge, paper, polymeric materials (see supplementary materials Figure S4-S8).
Experimental Section Materials: Dopamine was purchased from Acros Organic. Octadecylamine (ODA) and tris (hydroxymethyl) aminomethane (Tris) were obtained from Shanghai Chemical Regent Co. Fabrics are commercially available polyester fabric (double-faced pile). Methods: Firstly, ODA was added in deionized water by supersonic stirring to form an ivory-white emulsion. Then, ODA emulsion was dispersed in Tris-HCl (pH = 8.5) buffer with 0.5 mg/mL dopamine and a piece of clean fabric was soaked to the as-prepared mixture for 24 h at ambient temperature. Finally, the resulting brown textile was washed with ethanol and deionized water to remove the residuals, and then dried at room temperature for 12 h. Plasma Treatment: The sample was subjected to an oxygen plasma treatment using a plasma machine (Diener Electronic, small 2014, DOI: 10.1002/smll.201402383
Germany) for each 30 s plasma treatment. Such a plasma treatment can make the sample completely hydrophilic (contact angle: 0°). The plasma treated fabric was heated at 80 °C for 20 min. Then contact angle was measured again after self-healing. Washing Durability: The washing durability was evaluated using a laundering machine (Haier Co., Ltd, Qingdao, China). The fabric sample was laundered in 12 L water and with standard washing mode at 25 °C. After 45 min laundering, the sample was taken out and dried at room temperature, then the contact angle was measured. Healing was performed by heating the damaged sample at 80 °C for 20 min. Then, contact angle was measured again after self-healing. Abrasion Test: The abrasion durability was tested using a dry crocking method according to the GB/T 3920–2008 standard. The fabric sample was fixed on a dynamic disk which was brought into contact with an abradant superjacent. Uncoated fabric was used as abradant, and the abradant was fixed on a separate motionless disk. A loading pressure of 10 kPa was employed. During the test, the dynamic disk moved to and fro, in which the movement rate was 200 mm/min and the reciprocate stroke was 40 mm. Dyeing Method: In order to prettify the fabric modified with PDA@ODA nanocapsules, the fabric was dyed with rose red, orange, and blue colors. The coated cotton fabric was treated using oxygen plasma and then dipped in three kinds of dyebaths respectively (1% azaleine solution, 1% methyl orange solution, and 1% methylene blue solution) for 10 min. The unfixed dye was removed by water rinsing and then the dyed fabric was dried in oven at 80 °C for 20 min. Characterization: Sessile water-droplet contact angle (CA) values were acquired using a DSA-100 optical contact-angle meter (Kruss Co., Ltd., Germany) at ambient temperature. A 10 µL amount of deionized water, juice, coffee, milk were respectively dropped
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onto the samples using an automatic dispense controller, and the CAs were determined automatically using the Laplace-Young fitting algorithm. Average CA values were obtained by measuring the sample at five different positions, and images were captured with a digital camera (Sony, Ltd., Japan). SEM images were obtained on a JSM-6701F field emission scanning electron microscope (FESEM, Japan) at 5–10 kV, and TEM images were obtained on a FEI Tecnai G2 F30 transmission electronic microscope. Fourier transform infrared (FT-IR) spectroscopy was performed to investigate the characteristics of the specimens with KBr pellets on a Nicolet is 10 instrument (Thermo Scientific). All the photos were taken using a Canon camera.
Supporting Information Supporting Information is available from the Wiley Online Library or from the author.
Acknowledgements This research project was financially supported by the National Natural Science Foundation of China (51203173, 21303233 and 51335010). [1] H. X. Wang, H. Zhou, A. Gestos, J. F. Fang, H. T. Niu, J. Ding, T. Lin, Soft Matter 2013, 9, 277–282. [2] C. Shillingford, N. MacCallum, T. S. Wong, P. Kim, J. Aizenberg, Nanotechnology 2014, 25, 014019. [3] C. H. Xue, J. Z. Ma, J. Mater. Chem. A. 2013, 1, 4146–4161. [4] S. Li, S. Zhang, X. Wang, Langmuir 2008, 24, 5585– 5590.
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Received: August 9, 2014 Published online:
small 2014, DOI: 10.1002/smll.201402383
