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Surfaces, Interfaces, and Applications

Superhydrophilic, Underwater Directional Oiltransport Fabrics with a Novel Oil Trapping Function Sida Fu, Hua Zhou, Hongxia Wang, Haitao Niu, Weidong Yang, Hao Shao, Jinnan Wang, and Tong Lin ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b06533 • Publication Date (Web): 10 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

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ACS Applied Materials & Interfaces

Superhydrophilic, Underwater Directional Oil-transport Fabrics with a Novel Oil Trapping Function Sida Fua#, Hua Zhoua#, Hongxia Wang*a, Haitao Niua, Weidong Yangb, Hao Shaoa, Jinnan Wangc, Tong Lin*a a

Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia

b

Future Manufacturing Flagship, CSIRO, Clayton South, VIC 3169, Australia

c State

Key Laboratory of Pollution Control and Resource Reuse, School of the Environment,

Nanjing University, Nanjing 210023, China Corresponding authors’ emails: [email protected]; [email protected] KEYWORDS: superamphiphilic, underwater, directional oil transport, oil trapping ABSTRACT: In this study, we have prepared a novel superhydrophilic fabric that has underwater directional oil transport capability. The fabric was prepared using a two-step process consisting of dip-coating of a crosslinkable polymer, which comprises both oleophilic and hydrophilic groups, onto fabric substrate and single side UV irradiation of the coated fabric. The fabric had in air superhydrophilicity on the two side, and it can be wetted easily once immersed in water. The treated fabric showed underwater oleophobicity on the UV-exposed surface, whereas the unexposed back side still maintained underwater oleophilicity. At the optimized condition, the fabric in water transports oil automatically from the UV-exposed to the unexposed back side, but stops oil transport in the opposite direction. Such a directional oil transport takes place without the need for oil pre-wetting or formation of plastron layer on fabric. UV irradiation time showed an effect on oil transport ability. We further showed that the underwater directional oil transport fabric had a novel “oil trapping” ability. When used to seal a container, the fabric can trap oil into the

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container, and once trapped the oil was kept without releasing. This underwater directional oil transport fabric may be useful for development of high efficiency oil recovery systems.

1. Introduction Wettability driven directional liquid transport has received much attention owing to the proactive liquid transport capability and minimal requirement for external energy input1-4. It shows wide applications in smart textiles5, surface tension sensors6, oil-water separation7-10, water harvesting8, 11-12, microfluidic devices13 and aerosol oil mist filtration14. According to the type of liquid fluid to be transported, directional liquid transport can be divided into two main types: directional water transport (DWT) and directional oil transport (DOT). Two main strategies have been employed to prepare DWT fibrous membranes, 1) building a cross-plane hydrophobicity-to-hydrophilicity gradient along membrane thickness7, 15, and 2) forming opposite wettabilities in interconnected separate layers6, 11, 16. In 2010, Wang et al15 from our group first reported a DWT fabric fabricated by partial photo-degradation of a superhydrophobic fabric. Wu et al16 prepared a DWT nanofibrous membrane by electrospinning to form a dual-layer fibrous structure consisting of a hydrophilic layer and a hydrophobic layer. Zeng et al17 from our group prepared a DWT fabric by electrospraying a hydrophobic coating on one side of a hydrophilic fabric. Miao et al18 reported a trilayered fibrous membrane with progressive wettability. The middle layer assists to guide directional water transport continuously and spontaneously. Apart from those methods, other methods such as one-side vapor diffusion8, one-side O2/H2 plasma treatment8, and tightly stacking a hydrophobic metal mesh with hydrophilic fabric11 were reported. Recently, all-hydrophilic porous materials with asymmetric pores were also reported to be able to guide directional water transport19.

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DOT membranes were prepared using the approaches similar to preparation of DWT fabrics. Due to the multiplicity of oil fluids, however, a DOT membrane usually works selectively to the oils with a specific range of surface tension8, 20. Some DOT membranes show enhanced ability to recover oil from water6. A series of DOT membranes with DOT capability for oil fluids of different surface tensions were used for probing the surface tension of unknown oil fluids6. Most of the directional fluid transport fabrics reported so far work at a dry state in air. Recently, considerable interest has been devoted to superwettability in underwater environment. A few papers have reported about underwater directional oil transport (UW-DOT) across fabrics. However, most of the UW-DOT property had to be achieved under the condition that the fabric was either pre-wetted with oil8, 20 or able to form a plastron layer on the oleophilic surface21 (see a summary about UW-DOT materials in Supporting Information Table S1), which not only increase preparation complicity but also reduce the use reliability. However, UW-DOT functioning without preconditions has been less reported. In this study, we prepare a novel UW-DOT fabric using a dip coating method to apply a crosslinkable polymer, consisting of oleophilic and hydrophilic functional groups to fabric substrate, and by subsequently irradiating the coated fabric with UV light just on one side. A commercial polyester (PET) fabric was used as a model fabric substrate. The fabric showed in air superhydrophilicity on the two side, and it can be wetted easily once immersed in water. In water, the fabric can transport oil from the UV-exposed side to the unexposed back side, but it prevents oil from transport in the opposite direction. There was no oil pre-wetting or formation of plastron layer required to assist in oil transport. UV-irradiation time showed an effect on underwater oil transport feature. Longer irradiation hour led to no transport on the two sides. We further showed that such a UW-DOT fabric had a novel “oil trapping” capability. When used to seal a container, the UW-DOT fabric in water can trap oil into the container, and once trapped the oil was kept into

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the container without release. Such an oil locking function is unique, unachievable by other superwettability fabrics, such as oleophobic and oleophilic fabrics.

2. Results and discussion The UW-DOT fabric was fabricated by a two-step treatment method as schematically illustrated in Figure 1a. A commercial PET fabric was used as a model substrate. Firstly, the fabric substrate was dip-coated with a coating solution consisting of octadecylamine (ODA) and glycerol propoxylate triglycidyl ether (GPTE). This treatment allowed the fabric to have a superamphiphilic surface with 0° contact angle (CA) for both water and oil fluids (surface tension 18.4-72.8 mN m1)22.

The fabric showed almost identical surface wettability feature on the two sides. In the second

step, the coated fabric was UV irradiated (UV lamp wavelength mainly at 254 nm, intensity 38 mW/cm2) just on one side. After 2 hours of UV irradiation, the fabric was still superhydrophilic on both sides; however, in underwater environment, it showed a directional oil transport feature. Figures 1b & c show the scanning electron microscope (SEM) images of the treated fabric. After coating treatment, a conformal coating layer was formed on the fibers (Supporting Information Figure S1). After UV irradiation for 2 hours, both the UV exposed surface and the unexposed back side were almost unchanged in surface morphology. Atomic force microscope (AFM) imaging confirmed that the morphology had little change after UV irradiation (Figures 1d & e). In addition, the UV irradiation showed little effect on air permeability (Supporting Information Figure S2). These results indicate that UV treatment did not alter fibrous structure.

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Figure 1. a) Schematic of the procedure for dip-coating and UV irradiation, b) SEM image of coated fiber 2 hours UV irradiation side, and c) SEM image of coated fiber on the unexposed side (i.e. back side), d) AFM image of the coated fiber after (2 hour UV irradiated side), e) AFM image of the coated fiber on the unexposed side.

Figure 2 shows the results about wettability and underwater oil transport performance of the coated fabric after single side UV irradiation for 2 hours. At dry state in air, the fabric was superhydrophilic and superoleophilic (i.e. superamphiphilic) on both sides. When water was dropped on the fabric, it took 1.5 s for water to spread into the fabric (Figure 2a). It took shorter time, around 0.15 s, for hexane to spread into the fabric (Figure 2a). The two sides, i.e. UV exposed and unexposed, showed similar wetting feature of both water and hexane. When the UV irradiated fabric was immersed in water, it was wetted immediately. In underwater state, when hexane (~ 10 µL) was dropped to approach the UV exposed surface, it penetrated through the fabric and spread into the back layer (Figure 2c, also see Video S1). When hexane was dropped onto the back side, i.e. unexposed side, however, the hexane droplet spread along the surface without penetration through the fabric (Figure 2d, see Video S2). Therefore, the

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fabric showed a typical underwater directional oil transport characteristic, which is similar to the directional fluid transport reported on dry fabric in air7, 15.

Figure 2. Dropping a) water (5 µL) and b) hexane (5 µL) on the 2 hour UV treated fabric in air; c) & d) schematic illustration of UW-DOT effect and images taken from videos to show dropping hexane (~ 10 µL) onto the UW-DOT fabric; e) change of CA during dropping hexane on the 2 hour UV-irradiated fabric; f) CLSM image of the 2 hour UV irradiated fabric. The oleophobic layer was wetted by water containing florescent dye and the oleophilic layer was wetted by hexane.

Figure 2e shows the change of underwater contact angle (CAunderwater) with time when dropping hexane (~ 10 µL) on the fabric (2 hour UV treated). On the UV exposed side, the hexane CAunderwater decayed from 154° to 0° in 12 s. On the back side, the hexane CAunderwater reduced from 98° to 0° in 10 s. Although the change of the oil CA on the two sides showed a similar trend, oil droplets behaved differently. On the UV-irradiated front surface, oil penetrated through the fabric, whereas on the unexposed side, oil droplet just spread on the surface layer. These results are similar

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to the previous reports on directional oil transport fabrics7,

15,

expect for that the previously

reported DOT happened in dry state in air rather than in underwater environment. It has been established that the liquid repellent layer thickness plays a key role in deciding directional fluid transport property on fabric5. Here, we measured the underwater oleophobic layer thickness of the UV-treaded fabric using a scanning confocal microscope. As shown in Figure 2f, the portion with red fluorescence comes from oleophobic layer. It had a thickness around 186 μm. Such an underwater oleophobic layer thickness is similar to the hydrophobic layer thickness (~250 μm) for an in-air directional water transport fabric7. The chemistry features of the coated fabric before and after UV irradiation was examined by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Figure 3a shows the FTIR spectra. On the UV exposed surface, the peak at 3433 cm-1 was strengthened, suggesting increase in hydroxyl (-OH) groups. For the coated fabric without UV irradiation, peaks at 2971 and 2920 cm-1 were observed, which correspond to the asymmetric and symmetric vibrations of methylene (–CH2–) in alkyl group. After UV irradiation, on the UV exposed surface the peaks of methylene reduced observably, attributable to the decomposition of alkyl chains. However, the unexposed side showed little change. These results suggest that polarity groups are introduced to the UV exposed surface.

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Figure 3. a) FTIR spectra of coated fiber before and after 2 hour UV treatment, b) XPS survey spectra of coated fiber after 2 hour UV treatment, c) & d) XPS high-resolution C1s spectra of c) UV treated (2 hours) side and d) back side.

Figure 3b shows XPS survey spectra of both sides of the fabrics after UV irradiation. The fabric showed elements C, O, and N on the surface (see the element content data in Supporting Information Table S2). After UV irradiation, UV exposed side showed that the carbon atomic content decreased and oxygen atomic content increased, whereas the nitrogen atomic content showed little change, because of the introduce of polar groups, such as OH, COOH, and C=O. XPS high-resolution C1s spectrum of UV irradiated side is shown in Figure 1c. The peak at binding energy 290.3 eV was attributed to the C-N. The peak at binding energy 289.8 eV was attributed to the COOH groups. The peak at 288.7 eV was attributed to epoxy group. The peak at 287.6 eV was 8


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assigned to C=O group. The peak at 286.7 eV was assigned to C-O group. The peak at 286 eV corresponded to C-OH group. The peak at 285.8 eV was corresponded to C-C and C-H groups. In addition, N1s also showed peak at 401.1 eV (Supporting Information Figure S3a). XPS highresolution C1s spectrum of unexposed side is shown in Figure 3d and Figures S3b, which showed the similar results to the coated fabric22. These results confirmed that the coated fabric after UV irradiation showed increase in hydroxyl, carbonyl and carboxyl groups, which will increase hydrophilicity and underwater oleophobicity. The above results were obtained from the GPTE-ODA coated fabric with 2 hours of single side UV irradiation. We also examined the effect of UV irradiation time on surface wettability and liquid transport ability. It was found that the fabric showed UW-DOT property when the UV irradiation time varied in the range of 2-6 hours. The UV irradiation time affected the oil transport. For the 2 hour UV irradiated fabric, it took 12 s for hexane to transport from the UV exposed to the unexposed side. Longer irradiation time led to increase transport time. For the 6 hour UV irradiated fabric, transport of the same volume of hexane in this way took over 30 s (Figure 4a). This is presumably due to that increasing irradiation time leads to thicker underwater superoleophobic layer. In addition, UV irradiation time also affected oil spreading time on the unexposed side. With increasing the UV irradiation time from 2 to 6 hours, the oil spreading time increased from 12 s to 29 s (Figure 4a). When UV irradiation time was longer than 6 hours, oil cannot penetrate through the fabric from both sides due to stronger oleophobicity. Figure 4b shows CAunderwater of a hexane droplet on the 10 hour UV-irradiated fabric. During 24 hours of immersion in water, the droplet on the UV exposed side had a very small change in CAunderwater from 159° to 154°. The unexposed back maintained the original superoleophilicity CAunderwater of 0°. The immersion time showed almost no effect on (Supporting Information Figure S4). On the contrary, when the coated fabric was

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irradiated by UV light for just 1 hour, it maintained the dual-directional underwater oil transport property (Supporting Information Table S3).

Figure 4. a) Change of hexane CAunderwater with time for 10 hour UV irradiated fabric; b) oil transport time (from UV exposed to unexposed side) and spreading time (in unexposed side) for the UW-DOT fabrics prepared by UV different irradiation times; c, d) effect of UV irradiation time on CAunderwater of the fabric on c) UV exposed side, d) back side; e) 1, 2) photos of water and diesel dropped on the GPTE coated fabrics (in air): 1) non-UV treated sample, 2) 4 hour UV irradiated; 3-5) photos of diesel dropped on the surface of the GPTE coated fabric in underwater state: 3) non-UV treated sample, 4) UV treated (exposed side), 5) UV treated (unexposed side); f) 1, 2) photos of water and diesel dropped on the ODA coated fabrics (in air): 1) non-UV treated

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sample, 2) 4 hour UV irradiated; 3-5) photos of diesel dropped on the surface of the ODA coated fabric in underwater state: 3) non-UV treated sample, 4) UV treated (exposed side), 5) UV treated (unexposed side).

Figure 4c shows the change of the UV exposed surface CAunderwater with UV irradiation time. For comparison, the contact angle result for the non-irradiated fabric, i.e. just GPTE-ODA coated, is also included. For the non-irradiated fabric, it exhibited underwater superamphiphilicity for hexane, diesel, and gasoline (see Hexane result in Supporting Information Figure S5). After 1 hour of irradiation, the exposed surface increased the CAunderwater to 117° and 95° for hexane and diesel, respectively, however, CAunderwater for gasoline was still 0°. 2 hour UV treatment rendered the UV exposed surface with CAunderwater of over 154° only for hexane. In the range of 2-10 hours, the UV exposed surface maintained the CAunderwater almost unchanged. After 3 hour irradiation, the UV exposed surface showed CAunderwater over 151° for diesel, and such a high CAunderwater did not change with UV irradiation time even if the irradiation time was 10 hours. For gasoline, the CAunderwater increased in a much slower rate with UV irradiation time. After 9 hours of UV irradiation, the CAunderwater for gasoline incased to 158°. Though these changes in CAunderwater of the UV-exposed surface, the unexposed back surface did not change CAunderwater with UV irradiation. Even after 10 hours of UV irradiation, CAunderwater for the studied oil was 0° (Figure 4d). Here it should be pointed out that the single-side UV irradiation treatment shows little effect on the in air wettability. After 10 hours of UV irradiation, the dry fabric still has a superamphiphilicity in air, with contact angle of 0° for water and the oils studied (Supporting Information Table S4). We also investigated the transport properties of diesel and gasoline (surface tension 21.56 mN m-1 and 28.3 mN m-1) on the UV irradiated fabrics. As expected, the fabric showed UW-DOT

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property when the UV irradiation time was in the range of 3-5 hours, while the treatment time changed to 7-8 hours for gasoline (Supporting Information Figure S6 & Figure S7). The UV irradiated fabric showed reasonable stability. It can maintain the UW-DOT function for at least 5 days in ambient condition. After 6 days, the fabric started losing the underwater directional oil transport property. In previous papers, we reported the preparation of in-air directional fluid transport fabrics using single side UV degradation method7, 15. However, the fluid motion always takes place from the UV unexposed surface to the UV exposed surface. Here, the UV irradiated fabric showed a reverse oil motion, from the UV exposed surface to the UV unexposed side. In addition, the UWDOT took place easily in water without any pre-wetting or existence of plastron layer. A series of control experiments were conducted to probe the role of coating ingredients in surface wettability and oil transport property. When the fabric substrate was coated just by GPTE, it showed in air superamphiphilicity (Figure 4e) with contact angle of 0° for both water and oil. When immersed in water, however, the coated fabric became oleophobic (CAunderwater 145° for diesel, Figure 4e-2). When the GPTE coated fabric was subjected to a single-side UV irradiation for 4 hours, it still maintained the in-air superamphiphilic property on both sides (Figure 4e-3). In underwater environment, the fabric showed oleophobicity on both sides, and the UV irradiated and the non-irradiated surfaces had a similar CAunderwater, being around 145° for diesel (Figure 4e-4, 5). When the fabric was only coated with ODA, it showed hydrophobic-superoleophilic in air with a water contact angle of 138° and diesel contact angle of 0° (Figure 4f-1). In underwater state, the ODA coated fabric became superoleophilic (Figure 4f-2), having CAunderwater of 0° for diesel. When the ODA coated fabric was subjected to a single-side UV irradiation for 4 hours, the irradiated side became superamphiphilic in air (Figure 4f-3), while the unexposed side maintained the in air hydrophobicity-superoleophilicity. In water, however, the fabric showed superoleophilicity on

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both sides (Figure 4f-4, 5). Adjusting irradiation time (1-6 hours) did not alter the wettability change trend and no underwater oil transport was observed on the treated fabrics. In addition, the fabrics coated with GPTE and ODA and UV irradiation showed similar results on hexane (Supporting Information Figure S8). The above results suggest that coating treatment of fabric just with single ingredient, either GPTE or ODA, plus single side UV irradiation in the same condition did not result in underwater directional oil transport on the fabric. The underwater directional oil transport property should come from a joint action of GPTE and ODA, as well as the single side UV irradiation treatment. Based on the above results presented, the UW-DOT was proposed as schematically illustrated in Figure 5. The UV irradiation treatment does not affect the fibrous structure expect for the surface properties. Therefore, the underwater directional oil transport is originated from special surface properties of the fabric. This was similar to in-air directional fluid-transport fabrics7, 14-15. UV irradiation leads to the formation of underwater oleophobic surface on the UV irradiated surface, whereas the UV unexposed surface was almost unchanged in surface properties due to the low UV light intensity received (Figure 5a). A gradient wettability from underwater superoleophobicity to underwater oleophilicity will form after UV irradiation. This could be the driving force for the UW-DOT property, which is similar to in-air directional fluid transport fabrics7. The unexposed surface shows higher affinity to oil than water. In underwater environment, even if the fiber surface is fully wetted with water, oil can still spread easily into the unexposed fabric matrix (see Figure 5b top line). The larger affinity to oil than water is originated from the chemistry feature of the coating22. However, oil can just spread into the back side surface, without wetting the opposite UV irradiated surface because of the strong oleophobicity of the UV irradiated surface. When dropping oil to the UV exposed oleophobic surface, oil driven by the capillary force

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penetrates the thin oleophobic layer, and then moves to spread along the upper oleophilic surface (i.e. unexposed) (Figure 5b bottom line). Here it should be pointed out that the surrounding water in the oleophilic zone provides extra resistance to oil spreading. Only when the surface has a much higher affinity to oil than water can it overcome the hydration effect to allow oil spread into the matrix. The reasons for oil pre-wetting or forming a plastron layer that were reported in the previous papers on underwater directional oil transport fabrics were mainly due to inadequate in underwater oleophilicity and low affinity of water-wetted surface to oil. They both prevent oil from spreading in the oleophilic layer even if the oil can penetrate through the fabric from the opposite side. When the oleophilic side is pre-wetted with oil, the transported oil can merge into the pre-wetted oil layer with little resistance from water. In contrast, a plastron layer can also isolate water from the oleophilic zone. In this way, oil once breaking through the fabric from the opposite side can wick into the air-filled oleophilic layer without receiving the influence of surrounding water. Our UW-DOT differs from these pre-conditioned UW-DOT in that the oleophilic layer has already been hydrated with water (because of the hydrophilicity) and oil transported from the opposite side has to overcome the hydration effect before spreading into the oleophilicity layer. This requires the surface to be not only hydrophilic and oleophilic but also have much stronger affinity to oil than water.

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Figure 5. Schematic illustration of a) wettability change and b) UW-DOT mechanism.

One of the promising applications of UW-DOT materials is collection of oil spills from water. Oil contamination of water has become a spreading global issue in various fields such as industry, agriculture and our daily life. As such, removal of oil from water is important for industry production and environment protection23-25. Conventional oil recovery methods include absorbing with an oil absorber, burning, and spraying dispersants which are harmful to the environment26. A few papers have reported the use of UW-DOT materials for oil–water separation8, 20-21, which can only be used at preset conditions (see Table S1). Our UW-DOT fabric membrane showed promising in collecting oil from water. Figure 6 illustrates the potential application of our UW-DOT fabrics for oil collection. Here hexane was used an oil model. Two UW-DOT fabrics were put separately on the two ends of a glass tube with oleophobic surface faced outside (Figure 5b). In water, when oil contacted the

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fabric, it was transported into the container (Figure 5b, also see Video S3 in Supporting Information). However, once collected, the oil was locked into the container without release regardless of the locations (Supporting Information Figure S9, Video S4). The UW-DOT fabrics functioned like a one-way valve to trap and lock the oil.

Figure 6. a) Schematic illustration of underwater oil trapping (fabric is 2 hours UV treated); b) oil collection by a glass tube sealed with UW-DOT fabric (outer surface oleophobic), c)-e) control

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experiment to show oil collection using c) cotton fabric, d) untreated polyester fabric, e) PVDFHFP treated polyester fabric to seal the glass tube.

For comparison, we also tested other fabrics which had underwater oleophobicity (e.g. cotton fabric, (Figure 6c, Video S5), hydrophobic but underwater oleophilicity (uncoated polyester fabric Figure 6d, Video S6) and superhydrophobicity but underwater oleophilicity (PVDF-HFP treated polyester fabric Figure 6e, Video S7) (see the wettability feature in Table S5). They clearly show that both underwater oleophobic and underwater oleophilic fabrics cannot trap oil into the container. Although underwater oleophilic fabrics allowed oil spreading into the fabric matrix, they released the oil into the outer space. These results verify the unique behavior of our UW-DOT fabrics in oil collection. The oil separation for our directional oil transport fabrics follows a different principle to the conventional oil separation materials which are based on superhydrophobic-superoleophilic surface properties. For the conventional oil separation materials, oil is absorbed and stored into the porous materials until the pores are saturated. To recover the oil, the absorbed oil needs to be squeezed out so that the oil absorption material can be reused. For our UW-DOT fabrics, they are used mainly as a separating membrane with small storage capacity. The oil separated needs to be stored in an auxiliary container. In principle, the volume of the auxiliary container will decide its collection capacity. When the container is linked to a pipeline for oil transport, the system can collecting oil with unlimited ability. The treated fabric functions like a pump to selectively remove oil droplets from water, making the process continuous for large-area collection of oil spill. Although we used PET fabric as a model to prove this UW-DOT and the novel underwater “oil trapping” function, it should be suitable for treatment of other fabrics. Further improvement of treatment process and durability might lead to applications in practice.

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3. Conclusion We have prepared a novel superhydrophilic fabric with underwater directional oil transport function by pre-coating to make the fabric have a superamphiphilic surface and by subsequent single-side photo-degradation to create an underwater oleophobicity-to-oleophilicity across the thickness. The fabric after treatment maintains the superhydrophilicity on both sides, and just by immersing the fabric in water it can transport oil unidirectionally through the fabric. No oil prewetting is needed, and the treated fabric shows no plastron layer either. The oleophilic layer with stronger affinity to oil than water is critical to facilitate oil spreading in hydrated surface without oil pre-wetting or forming plastron layer. The fabric shows unique ability to trapping oil from water. This novel underwater directional oil-transport fabric may find applications in development of advanced oil recovery technology and devices.

4. Experimental Section Materials: Glycerol propoxylate triglycidyl ether (GPTE, molecular weight 434, epoxy value 0.69) was supplied by Alfa Chemistry and used as received. Octadecylamine (ODA), 1methylimidazole, ethanol, hexane, acid yellow, and oil blue were provided by Sigma-Aldrich. Polyester fabric (plain weave, 168 g·m-2, thickness ≈ 420 μm) was obtained from a local textile shop, and it was cleaned with acetone and distilled water before use. Preparation of underwater directional oil transport fabric: In first step, the amphibious superamphiphilic fabric was prepared according to our previous work. 5 g GPTE and a drop of 1methylimidazole were added to 50 ml ethanol and then stirred for 30 min. 1 g ODA was added to the GPTE solution and stirred overnight. The slight turbid solution further stirred for 15 min at 50 °C. After that, a transparent solution was prepared for coating. In second step, the coated polyester 18


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fabric was irradiated under a UV lamp (model EPS-100/F, Spectroline, wavelength mainly at 254 nm, intensity 38 mW/cm2) just from one fabric side. After irradiation, the fabric showed an underwater directional oil transport property. Characterizations: An SEM (Supra 55VP operated at an acceleration voltage of 5.0 kV) was used to observed the coating morphology. The underwater oleophobic layer thickness was measured on a scanning confocal microscope (LSCM, Leica TCS SP8). Before testing, the fabric sample water wetted with water containing Rhodamine B (1.0 wt%), a red fluorescent dye. The wetted sample was then immersed in oil. In this way, the water in the oleophilic zone was replaced by oil, leaving the oleophobic layer still wetted with the dye-containing water. The contact angle was measured on a Contact Angle Meter (KSV Model CAM 101) with liquid of 5 µL in volume. The spreading time was measured using a Contact Angle Meter (interval time is 0.033 s). FTIR spectra were measured in Attenuated Total Reflection mode using a Burker Vetex 70 instrument. The spectra were recorded under 64 scans at 4 cm-1 resolution. The XPS spectra were obtained on a VG ESCALAB 220-iXL XPS spectrometer with a monochromated AL Kα source (1486.6 eV) using samples of ~3 mm2 in size. The collected XPS results were analyzed by the CasaXPS software. AFM was conducted with a Cypher AFM (Asylum Research) using the tapping model. Air permeability was measured using an air permeability tester (FX 3300 air permeability tester III, Zurich, Switzerland) according to standard BS 5'636 (Great Britain). Test area was 5 cm2. Air pressure was set at 98 Pa. Six repeats were averaged for each test.

ASSOCIATED CONTENT Supporting Information: includes SEM images of the coated fiber, air permeability of fabric, photo of fabric, spreading time for UW-DOT fabrics, and tables to summarize underwater directional oil transport in porous structures, spreading time, element contents and wettability.

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AUTHOR INFORMATION Corresponding authors’ email: [email protected]; [email protected] # Sida

Fu and Hua Zhou contributed equally to this paper.

The authors declare no competing financial interest.

ACKNOWLEDGMENT The authors thank funding support from an Australian Research Council Discovery Project (DP190100306), Alfred Deakin Postdoctoral Fellowship (to H. Z.), and Institute for Frontier Materials (IFM) Research Excellence Grants scheme 2018.

REFERENCES (1)

Zheng, Y.; Bai, H.; Huang, Z.; Tian, X.; Nie, F.-Q.; Zhao, Y.; Zhai, J.; Jiang, L. Directional

Water Collection On Wetted Spider Silk. Nature 2010, 463 (7281), 640. (2)

Kong, Y.; Liu, Y.; Xin, J. H. J. J. o. M. C. Fabrics With Self-Adaptive Wettability

Controlled By “Light-And-Dark”. J. Mater. Chem. 2011, 21 (44), 17978-17987. (3)

Zhao, Y.; Wang, H.; Zhou, H.; Lin, T. Directional Fluid Transport in Thin Porous Materials

and its Functional Applications. Small 2017, 13 (4), 1601070. (4)

Cui, Y.; Li, D.; Bai, H. Bioinspired Smart Materials for Directional Liquid Transport. Ind.

Eng. Chem. Res. 2017, 56 (17), 4887-4897. (5)

Sarkar, M.; Fan, J.; Szeto, Y.-c.; Tao, X. Biomimetics Of Plant Structure In Textile Fabrics

For The Improvement Of Water Transport Properties. Text. Res. J. 2009, 79 (7), 657-668.

20


Page 20 of 31

Page 21 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(6)

Wang, H.; Zhou, H.; Yang, W.; Zhao, Y.; Fang, J.; Lin, T. Selective, Spontaneous One-

Way Oil-Transport Fabrics And Their Novel Use For Gauging Liquid Surface Tension. ACS Appl. Mater. Interfaces 2015, 7 (41), 22874-22880. (7)

Zhou, H.; Wang, H.; Niu, H.; Lin, T. Superphobicity/Philicity Janus Fabrics With

Switchable, Spontaneous, Directional Transport Ability To Water And Oil Fluids. Sci. Rep. 2013, 3, 2964. (8)

Tian, X.; Jin, H.; Sainio, J.; Ras, R. H.; Ikkala, O. Droplet And Fluid Gating By Biomimetic

Janus Membranes. Adv. Funct. Mater. 2014, 24 (38), 6023-6028. (9)

Wang, H.; Zhou, H.; Niu, H.; Zhang, J.; Du, Y.; Lin, T. Dual ‐ Layer

Superamphiphobic/Superhydrophobic‐Oleophilic Nanofibrous Membranes With Unidirectional Oil ‐ Transport Ability And Strengthened Oil–Water Separation Performance. Adv. Mater. Interfaces. 2015, 2 (4), 1400506. (10)

Li, N.; Yu, C.; Si, Y.; Song, M.; Dong, Z.; Jiang, L. Janus Gradient Meshes for Continuous

Separation and Collection of Flowing Oils under Water. ACS Appl. Mater. Interfaces 2018, 10 (8), 7504-7511. (11)

Cao, M.; Xiao, J.; Yu, C.; Li, K.; Jiang, L. Hydrophobic/Hydrophilic Cooperative Janus

System For Enhancement Of Fog Collection. Small 2015, 11 (34), 4379-4384. (12)

Jiang, J.; Gao, J.; Zhang, H.; He, W.; Zhang, J.; Daniel, D.; Yao, X. Directional Pumping

Of Water And Oil Microdroplets On Slippery Surface. Proceedings of the National Academy of Sciences 2019, 116 (7), 2482-2487. (13)

Buchberger, G.; Hischen, F.; Comanns, P.; Baumgartner, R.; Kogler, A.; Buchsbaum, A.;

Bauer, S.; Baumgartner, W. Bio-Inspired Microfluidic Devices For Passive, Directional Liquid Transport: Model-Based Adaption For Different Materials. Procedia Eng. 2015, 120, 106-111.

21



(14)

Wei, X.; Zhou, H.; Chen, F.; Wang, H.; Ji, Z.; Lin, T. High-Efficiency Low-Resistance

Oil-Mist Coalescence Filtration Using Fibrous Filters with Thickness-Direction Asymmetric Wettability. Adv. Funct. Mater. 2019, 29 (1), 1806302. (15)

Wang, H.; Ding, J.; Dai, L.; Wang, X.; Lin, T. Directional Water-Transfer Through Fabrics

Induced By Asymmetric Wettability. J. Mater. Chem. 2010, 20 (37), 7938-7940. (16)

Wu, J.; Wang, N.; Wang, L.; Dong, H.; Zhao, Y.; Jiang, L. Unidirectional Water-

Penetration Composite Fibrous Film Via Electrospinning. Soft Matter 2012, 8 (22), 5996-5999. (17)

Zeng, C.; Wang, H.; Zhou, H.; Lin, T. Directional Water Transport Fabrics with Durable

Ultra‐High One‐Way Transport Capacity. Adv. Mater. Interfaces. 2016, 3 (14), 1600036. (18)

Miao, D.; Huang, Z.; Wang, X.; Yu, J.; Ding, B. Continuous, Spontaneous, and Directional

Water Transport in the Trilayered Fibrous Membranes for Functional Moisture Wicking Textiles. Small 2018, 14 (32), 1801527. (19)

Shou, D.; Fan, J. An All Hydrophilic Fluid Diode for Unidirectional Flow in Porous

Systems. Adv. Funct. Mater. 2018, 28 (36), 1800269. (20)

Zhang, Y.; Cao, M.; Peng, Y.; Jin, X.; Tian, D.; Liu, K.; Jiang, L. Bioinspired Continuous

and Spontaneous Antigravity Oil Collection and Transportation. Adv. Funct. Mater. 2018, 28 (5), 1704220. (21)

Li, H.; Cao, M.; Ma, X.; Zhang, Y.; Jin, X.; Liu, K.; Jiang, L. “Plug‐and‐Go”‐Type

Liquid Diode: Integrated Mesh with Janus Superwetting Properties. Adv. Mater. Interfaces. 2016, 3 (19), 1600276. (22)

Fu, S.; Zhou, H.; Wang, H.; Niu, H.; Yang, W.; Shao, H.; Lin, T. Amphibious

Superamphiphilic Fabrics with Self-healing Underwater Superoleophilicity. Mater Horiz. 2019, 6 (1), 122-129.

22


Page 22 of 31

Page 23 of 31 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23)

Xue, Z.; Wang, S.; Lin, L.; Chen, L.; Liu, M.; Feng, L.; Jiang, L. A Novel Superhydrophilic

And Underwater Superoleophobic Hydrogel‐Coated Mesh For Oil/Water Separation. Adv. Mater. 2011, 23 (37), 4270-4273. (24)

Zhang, J.; Seeger, S. Polyester Materials With Superwetting Silicone Nanofilaments For

Oil/Water Separation And Selective Oil Absorption. Adv. Funct. Mater. 2011, 21 (24), 4699-4704. (25)

Liu, Y.; Su, Y.; Guan, J.; Cao, J.; Zhang, R.; He, M.; Gao, K.; Zhou, L.; Jiang, Z. 2D

Heterostructure Membranes with Sunlight‐Driven Self‐Cleaning Ability for Highly Efficient Oil–Water Separation. Adv. Funct. Mater. 2018, 28 (13), 1706545. (26)

Wang,

C.-F.;

Tzeng,

F.-S.;

Chen,

H.-G.;

Chang,

C.-J.

Ultraviolet-durable

superhydrophobic zinc oxide-coated mesh films for surface and underwater–oil capture and transportation. Langmuir 2012, 28 (26), 10015-10019.

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Figure 1. a) Schematic of the procedure for dip-coating and UV irradiation, b) SEM image of coated fiber 2 hours UV irradiation side, and c) SEM image of coated fiber on the unexposed side (i.e. back side), d) AFM image of the coated fiber after (2 hour UV irradiated side), e) AFM image of the coated fiber on the unexposed side. 99x44mm (300 x 300 DPI)



Figure 2. Dropping a) water (5 µL) and b) hexane (5 µL) on the 2 hour UV treated fabric in air; c) & d) schematic illustration of UW-DOT effect and images taken from videos to show dropping hexane (~ 10 µL) onto the UW-DOT fabric; e) change of CA during dropping hexane on the 2 hour UV-irradiated fabric; f) CLSM image of the 2 hour UV irradiated fabric. The oleophobic layer was wetted by water containing florescent dye and the oleophilic layer was wetted by hexane. 99x51mm (300 x 300 DPI)


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Figure 3. a) FTIR spectra of coated fiber before and after 2 hour UV treatment, b) XPS survey spectra of coated fiber after 2 hour UV treatment, c) & d) XPS high-resolution C1s spectra of c) UV treated (2 hours) side and d) back side. 99x91mm (300 x 300 DPI)



Figure 4. a) Change of hexane CAunderwater with time for 10 hour UV irradiated fabric; b) oil transport time (from UV exposed to unexposed side) and spreading time (in unexposed side) for the UW-DOT fabrics prepared by UV different irradiation times; c, d) effect of UV irradiation time on CAunderwater of the fabric on c) UV exposed side, d) back side; e) 1, 2) photos of water and diesel dropped on the GPTE coated fabrics (in air): 1) non-UV treated sample, 2) 4 hour UV irradiated; 3-5) photos of diesel dropped on the surface of the GPTE coated fabric in underwater state: 3) non-UV treated sample, 4) UV treated (exposed side), 5) UV treated (unexposed side); f) 1, 2) photos of water and diesel dropped on the ODA coated fabrics (in air): 1) non-UV treated sample, 2) 4 hour UV irradiated; 3-5) photos of diesel dropped on the surface of the ODA coated fabric in underwater state: 3) non-UV treated sample, 4) UV treated (exposed side), 5) UV treated (unexposed side). 99x100mm (300 x 300 DPI)


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Figure 5. Schematic illustration of a) wettability change and b) UW-DOT mechanism. 99x74mm (300 x 300 DPI)



Figure 6. a) Schematic illustration of underwater oil trapping (fabric is 2 hours UV treated); b) oil collection by a glass tube sealed with UW-DOT fabric (outer surface oleophobic), c)-e) control experiment to show oil collection using c) cotton fabric, d) untreated polyester fabric, e) PVDF-HFP treated polyester fabric to seal the glass tube. 84x99mm (300 x 300 DPI)


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TOC 50x39mm (300 x 300 DPI)


Superhydrophilic, Underwater Directional Oil ... - ACS Publications

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