Multifunctional Directional Water Transport Fabrics with Moisture

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Cite This: ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

Multifunctional Directional Water Transport Fabrics with Moisture Sensing Capability Hongxia Wang,*,† Haitao Niu,† Hua Zhou,† Xin Wei,† Weidong Yang,‡ and Tong Lin*,† †

Institute for Frontier Materials, Deakin University, Geelong, VIC 3216, Australia Future Manufacturing Flagship, CSIRO, Clayton South, VIC 3169, Australia

‡

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S Supporting Information *

ABSTRACT: Previous fabrics with directional fluid transport capability typically have a single function to transport liquid. Multifunctional directional fluid fabrics are highly desirable for making “smart” textiles but remain a challenge to develop. In this study, we have for the first time prepared a multifunctional, directional water transport fabric. By using a two-step coating process, we applied polypyrrole (PPy), a conducting polymer, on one side of a hydrophilic fabric (cotton). We showed that the single-side PPy-coated fabrics had reasonable conductivity (surface resistance in the range of 43−54 kΩ/□) and a one-way water transport function. We further showed that by integrating metal-plated nylon wires on the two sides, the fabric can be used as a capacitive sensor to sense water content in the fabric. The conducting layer enables the sensor device to have a sufficient capacitance response. Reasonable integration of the metal electrodes allows the device to have a minimal effect on the directional water transport and breathability of the fabric. Such a novel multifunctional fabric may find applications in making “smart” clothing. KEYWORDS: directional water transport, conductivity, multifunctional, fabrics, moisture sensor

1. INTRODUCTION Fabrics that can transport liquid unidirectionally from one side of a fabric to another, also referred to as “directional fluid transport fabrics”, have received much attention because of the automatic, energy-free fluid manipulation capability. They have shown great potential in many fields including functional textiles, workwear, health/aged care, water−oil separation, water harvesting, and oil−gas separation.1−7 Directional water transport fabrics are prepared based on two main strategies: (1) cross-plane hydrophobicity-to-hydrophilicity gradient1 and (2) layered hydrophobic and hydrophilic structure.2 Wang et al.1,8,9 from our group first reported a single-side photodegradation method to prepare directional water transport fabrics. Wu et al.2 reported a directional water transport nanofibrous membrane prepared by an electrospinning method. Zhang et al.10,11 prepared a directional water transport membrane with a cross-plane hydrophilic-to-hydrophobic gradient using a phase separation method. Zeng et al.12 used a single-side electrospraying method to endow a hydrophilic fabric with a one-way water transport capability. Despite these studies, the directional water transport fabrics reported predominantly have a single function to transfer water from one side to another besides the intrinsic properties from the fabric substrate. Rendering directional water transport with multifunction will broaden the application scope and offer opportunities to develop novel functionality. However, there are few reports on multifunctional directional water transport fabrics in research literature. © 2019 American Chemical Society

One function that we have been trying to endow directional water transport with is moisture sensing because of the potential in monitoring the sweat rate.13−15 The sweat rate is known to be an important index to associate with body core temperature, variability, environmental conditions, heat acclimatization, nutrition, hydration status, illness, and disorders,16,17 hence signifying the individual performance18 useful for medical monitoring, health/aged care, sport, and personal protections.19 Sensors for detecting moisture content in fabrics were developed based on various principles such as electrical resistance, capacitance, and surface acoustic waves.14,20−22 The capacitive sensors are advantageous over the other sensor types owing to the high reliability, low energy consumption, and broad range.14 Several papers have reported the integration of film-based capacitive sensors into textile fabrics.15,23 However, embroidering film sensors in fabrics could influence the air permeability of the fabric. Fabric-based moisture sensors are desirable for the high breathability and softness to wear but are challenging to develop. In the earlier studies, we have prepared electrically conductive superhydrophobic fabrics using a vapor-phase polymerization technology.24,25 The fabric had a superhydrophobic surface (water contact angle of 169°) with Received: April 18, 2019 Accepted: June 4, 2019 Published: June 4, 2019 22878

DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

Research Article

ACS Applied Materials & Interfaces

Figure 1. (a) Scheme of single-side electrospray treatment and vapor-phase polymerization to prepare the PPy coating. (b) Polymerization reaction. (c, d) SEM images of the (c) uncoated cotton fabric and (d) PPy-coated cotton surface. (e) TEM image of the PPy-coated fiber (crosssectional view). (f) FTIR spectra and (g) XPS survey spectra of the cotton fabrics. (h) Photos to show the one side PPy-coated cotton fabric (inset, the magnified zone). V/s scan rate in a potential range of 0−3.0 V.20,21,26 The detection of water content inside the fabric was performed in a lab with the temperature and humidity conditioned at 25 °C and 50−60% RH, respectively. The air humidity was detected in a chamber at 25 °C, with the humidity adjustable in the range of 20−80% RH. The fabric in the dry state was used for this test. 2.5. Other Characterizations. Surface morphology was observed on a field emission electron microscope (FESEM, Leo 1530, Gemini/ Zeiss). The coating thickness was estimated using a transmission electron microscope (JEOL-2100F, Japan) at an accelerating voltage of 200 keV, and a Gatan image filter was used to assist in acquiring the images. The TEM samples were fabricated by embedding the cotton fibers in epoxy resin (45359 epoxy-embedding kit, Fluka). The solidified sample was sliced on a Leica EM UC6 ultramicrotome with a diamond knife to get 80 nm-thick slices. For coating thickness calculation, at least 30 measurements from 30 reads were used to calculate the average thickness. Fourier transform infrared (FTIR) spectra were measured in ATR mode on a Bruker Optics FTIR spectrometer (Ettlingen, Germany). Surface roughness was measured using a Cypher atomic force microscope (AFM) (Asylum Research). A commercial contact angle meter (KSV CAM101 Instruments Ltd.) was used to measure contact angles. The water droplets for contact angle measurement have a volume of 13 μL. A standard two-probe method (AATCC 76-1995) was used to measure the surface resistance of the coated fabrics. The liquid transport property was characterized according to the AATCC (American Association of Textile Chemists and Colorists) test method (AATCC 195-2011). An M290 MMT (Moisture Management Tester) and 0.9% NaCl were used for testing. Fabric samples were conditioned in the required environment (temperature, 21 ± 2 °C; RH, 65 ± 2%) for over 24 h before testing. The breakthrough pressure was measured using an apparatus developed in our previous study.1 During testing, the flow rate was set at 20 mL/min. A standard method (AATCC 61-2006 test no. 2A) was used to wash the fabric samples for washing durability evaluation. The washing was carried out in a standard laundry machine (Fong, Fong’s National Engineering Co. Ltd., Hong Kong, China) equipped with

reasonable conductivity. Such a multifunctional coating is patternable and can be used to form an electric circuit on fabrics. In this study, we for the first time prepare a novel fabric with directional water transport, single-side electrical conductivity, and moisture sensing functions. A cotton fabric was used as a model. When a thin layer of conducting polymer (polypyrrole in our study) was applied to one side of the fabric, it showed both directional water transport and electrical conductivity features. By integrating two metal-plated nylon wires (as electrodes) into the treated fabric, they are able to sense moisture within the fabric. The electrode integration showed a very little effect on directional water transport and air permeability of the fabric.

2. EXPERIMENTAL SECTION 2.1. Materials. Pyrrole (C4H5N), FeCl3·6H2O, and ethanol were obtained from Sigma-Aldrich and used without purification. A cotton (plain woven, 244 g/m2) fabric purchased from a local market was used as a substrate. A gold-plated textile wire (Cu/Au6; diameter, 200 μm) was obtained from Elektrisola Feindraht AG. 2.2. Single-Side Coating of Polypyrrole. An ethanol solution consisting of 10% (w/v) FeCl3 6H2O was electrosprayed to the cotton fabric on just one side. After drying at room temperature for 30 min, the as-sprayed fabric was placed into a chamber filled with pyrrole-saturated nitrogen. After 10 min, the fabric was taken out from the chamber, and it was then rinsed with ethanol and water to remove impurities. 2.3. Preparation of Fabric Sensor. The capacitive moisture sensor was prepared by stitching two gold-plated nylon wires separately on the two sides of the PPy-coated fabric. For comparison, the fabric without the PPy coating was also used for making fabric sensors. 2.4. Characterization of Sensor Properties. Capacitance was measured using an electrochemical workstation (CHI760D) at a 0.5 22879

DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

Research Article

ACS Applied Materials & Interfaces 500 mL (75 mm × 75 mm) stainless-steel lever-lock canisters. An AATCC standard reference detergent WOB (0.15%, w/w) and 50 stainless steel balls were added to a 150 mL aqueous solution for laundering the fabric sample (size, 50 mm × 150 mm). The laundering was performed at 49 °C and a 40 ± 2 rpm stirring speed for 45 min. After rinsing with tap water, the laundered sample was dried at room temperature. Such a washing treatment corresponds to five cycles of home machine laundering. In this paper, the equivalent number of home laundering cycles was reported. The air permeability test was performed according to the SIST EN ISO 9237:1999 standard using an FX 3300 air permeability tester, and the average value of 10 measurements was reported. A standard ASTM E96M16D was employed to measure the moisture permeability at 32.2 °C with an air speed of 0.26 m/s. A Martindale abrasion tester (IDM. Instrument Design and Maintenance) was used to test the abrasion resistance (standard ASTM D4966). The fabric sample was mounted on a dynamic disk to allow its contact with the abradant (untreated fabric), which was mounted on the base disk. A weight load was applied to the upper shaft to generate a 12 kPa pressure on the sample. During testing, the dynamic disk rotates on its axis, while the axis circulates across the abradant. Such a test is widely used for evaluation of heavy-duty upholstery fabrics prepared by a coating treatment.

N+ (bipolaron) bonds. These results suggest that PPy exists on the sprayed cotton fabric surface.30−32 It should be pointed out that PPy only formed just on the FeCl3-sprayed side of the fabric. The back side, which was not coated with FeCl3, showed the original morphology and chemical characteristics (Supporting Information). Figure 1h shows a photo of the treated cotton. The black spots viewed in the back view originate from the large pores of the fabric, which enable some PPy-coated areas to be seen from the back side. The cotton fabric without treatment shows a hydrophilic surface with a contact angle (CA) of 0° to water. Water droplets spread into the fabric immediately once they made contact with the cotton fabric (Supporting Information, Figure S5). For the cotton completely coated with PPy, it had a hydrophobic surface with a WCA of 147°. The water droplet (volume, 25 μL) on the PPy-coated fabric remained in a nearly spherical shape. The hydrophobicity was stable, allowing the water droplet to stay for long hours without spreading, which is in accordance with our previous report.24 Such a high hydrophobicity keeps it dry during contact with water. When the cotton fabric was single-side-coated with PPy, the coated side showed different surface properties to both the uncoated fabric and the one entirely coated with PPy. As seen in Figure 2a, when water dropped onto the PPy-coated surface

3. RESULTS AND DISCUSSION The fabric treatment procedure is illustrated in Figure 1a. A modified electrospray method was employed to apply FeCl3 solution to one side of the cotton fabric. After drying at room temperature, the electrosprayed cotton was placed to a chamber filled with pyrrole vapor. Polymerization took place once pyrrole made contact with FeCl3 (see the polymerization reaction in Figure 1b). After the reaction, the sprayed area turned black. This indicates that polypyrrole (PPy) forms on the fabric. The surface morphology can be observed by SEM imaging. As shown in Figure 1c,d, after coating with PPy, the fibers looked rougher (Figure 1d), indicating the deposition of solid materials on the surface. The rough surface was further confirmed by AFM imaging (Supporting Information). The PPy-coated fibers increased the root mean square roughness from 38.7 to 110.6 nm. TEM imaging verified that cotton fibers were indeed coated with a thin layer of material, with an average thickness of 83 nm (Figure 1e). Figure 1f shows the Fourier transform infrared spectroscopy (FTIR) spectra of the cotton fabrics. For the PPy-coated cotton, the strong vibration peaks at ∼1547 and 1452 cm−1 corresponding to the skeletal vibration and in-plane deformation vibration of pyrrole rings appeared. The bands at 1040 and 1312 cm−1 represented CH in-plane and C− N bond vibrations, respectively. The peak at 889 cm−1 originated from the out-of-plane vibration for CH.24,27 These results verify the formation of polypyrrole. Figure 1g shows the X-ray photoelectron spectroscopy (XPS) survey spectra. On the PPy-coated surface, elements C, N, and Cl appeared in the spectra. A trace amount of Fe (atomic content, 0.05%) was detected, which was attributed to the trapping of the polymer matrix. The existence of the trace Fe ions shows little effect on surface properties and conductivity. Cl ions in the PPy function as a dopant to ensure good conductivity of PPy.28,29 The high-resolution C 1s spectra indicated the occurrence of new peaks at 284 eV (assigned to β carbon of the pyrrole rings) and 285 eV (α carbon of the pyrrole rings). The peak at 286 eV came from CN, C−OH, and CNH+ (polaron) bonds. The peak at 287.6 eV originated from CO and −C

Figure 2. (a, b) Images taken from the videos recorded during dropping of water on the (a) PPy side and (b) back side. (c) WCA change with time for water droplets on the PPy-coated fabric. (d) Summary of the R value, air permeability, and surface resistance of the fabric. (Sample: cotton fabric with a PPy coating depth of ∼40 μm.)

(i.e., hydrophobic surface), it penetrated immediately the surface layer and spread along the opposite surface. When water was dropped onto the uncoated side (i.e., hydrophilic surface), however, it spread just along the surface layer without transporting to the PPy-coated side (Figure 2b). Figure 2c shows the water CA change when a water droplet is dropped on the PPy-coated fabric. On the PPy-coated side, the CA decreased from 147 to 0° in 4 s although the surface was hydrophobic. This is because water penetrated the coating layer and wicked into the uncoated cotton matrix. In this case, the PPy layer still remained non-wetted. On the unsprayed surface, the CA reduced from 73 to 0° within 1 s due to water spreading directly into the cotton matrix. Such water contact angle changes were also reported on other directional water transport fabrics.9,12,33 These results indicate that one-side PPy treatment enables the cotton fabric to have a directional water transport property. In addition, the treated fabric showed different breakthrough pressures between the two sides. From the PPy-coated to the uncoated side, the breakthrough pressure was 2.5 ± 0.2 cmH2O because of the resistance from the fabric matrix.9,12,33 22880

DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

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Figure 3. (a−c) Effects of PPy coating depth on (a) surface resistance, (b) R values, and (c) air permeability. (d−f) Effects of FeCl3 concentration in the electrospraying solution on (d) surface resistance, (e) R values, and (f) fabric air permeability of the PPy-coated fabric (PPy coating depth, ∼40 μm).

in the surface resistance to ∼42 kΩ. The increased conductivity can be explained by the fact that the increase in the PPy coating depth also improves the interfiber connection within the coated fibrous matrix. The PPy-coated side had a maximum R value when the PPy coating layer was ∼40 μm in thickness. Lower R values resulted when the coating depth was larger or smaller than ∼40 μm. In contrast, the R value on the back side always remains negative, and at a low coating depth, the R value on the back side showed a more negative value. These changing trends in the R value come from the effect of the PPy-coated hydrophobic layer on water transport. In addition, the air permeability reduced slightly with the increase in the PPy coating depth presumably due to the PPy coating reducing the pore size of the coated layer. With an increase in the PPy coating layer thickness, the portion of the smaller pore increases, leading to reduced air permeability (Figure 3c). To increase the conductivity of the PPy coating layer, we adjusted the FeCl3 concentration in the electrospraying solution. To ensure having a directional water transport property on the coated fabrics, we kept the coating depth at ∼40 μm. As shown in Figure 3d−f, with increasing the FeCl3 concentration from 1.0 to 20.0%, the surface resistance on the PPy-coated surface reduced from 170 ± 2 to 55 ± 0.2 kΩ/□. The increased conductivity originated from the thicker PPy coating layer formed from the solution of higher FeCl3 content, which increases the interfiber connection. Adjusting the FeCl3 concentration showed a very little effect on the R value (Figure 3e). This is because directional water transport property is mainly determined by the coating depth and surface wettability of the PPy. Increasing the FeCl3 concentration led to an increase in the PPy coating thickness on the cotton fibers. As a result, the pores in the coated area became smaller in size. As expected, a higher FeCl 3 concentration led to a little reduction in air permeability (Figure 3f) due to the reduced pore size in the coated fabric layer.

However, the pressure in the reverse direction was much higher, being 11.7 ± 1.3 cmH2O. The one-way transport capacity index (R value) was measured to quantitatively characterize the water transport ability. As listed in Figure 2d, the control cotton fabric had negative R values around −25 to −36% on both sides. For the single-side PPy-coated fabric, the PPy-coated side had an R value of 225%, whereas the R value for the uncoated back side was −85%. A negative R value suggests water accumulation on the feeding surface, whereas a positive value indicates that water tends to move through the fabric and wicks into the opposite side. The opposite R values between the two sides are indices of directional water transport fabrics.12 The effects of the PPy coating on air and moisture permeability were examined. For the single-side PPy-coated fabric, which had a directional water transport property, the two fabric sides showed similar air permeability, being 24.7 ± 0.5 cm3/cm2/s. The value was slightly lower than that of the uncoated fabric (29.2 cm3/cm2/s) because the PPy coating reduced the pore size of the coated layer. The moisture permeability of the coated fabric was determined according to a standard method (ASTM E96M-16D). At 50% humidity, the PPy-coated side had a moisture permeability of 0.457 g/m2 h, which was similar to that of the uncoated side (0.476 g/m2 h). In our previous studies,1,3,9,12 we have elucidated that wettability-driven directional water transport is highly dependent on the depth of the hydrophobic layer. Here, we found that when the depth of the PPy coating layer was smaller than 30 μm, a dual transport feature occurred on the treated cotton fabric, whereas nontransport on both sides resulted when the coating layer was thicker than 60 μm. When the PPy coating was in the range of 30−60 μm, the fabric showed a directional water transport property. The PPy coating thickness affects the surface resistance, R value, and air permeability, as shown in Figure 3a−c. When the coating depth was ∼20 μm, the surface resistance was 360 kΩ. Increasing the PPy coating depth to ∼80 μm led to a decrease 22881

DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

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ACS Applied Materials & Interfaces

Figure 4. (a) Illustration of the fabric sensor prototype. (b, c) Photos of the fabric sensor. (d) Capacitance at different air humidity levels. (e) Capacitance at different sweat loading levels. (f) Capacitance at different temperature levels (air humidity, 20%; sweat loading, 30 g/m2).

dialectic constant), and d is the interelectrode distance. When the medium between the electrodes is a solid or liquid substance

We further showed that this single-side, electrically conductive, directional water transport fabric can be used for preparing moisture sensors. To do this, we developed a device prototype based on the single-side PPy-coated fabric. Figure 4a illustrates the prototype device structure. Two gold-plated nylon wires were mounted on the fabric through stitching at selective spots. To ensure coverage of a large area, the Auplated wires were arranged in a nearly rectangular wave. A photo of the prototype device is shown in Figure 4b. The sensor device is flexible and can be bent and folded, as shown in Figure 4c. The metalized nylon thread had little effect on the water transport feature and air permeability of the fabric (Supporting Information). The R values for the prototype device were 182% (on the PPy side) and −67% (on the back side), and the air penetrability was 24.7 cm3/cm2/s. Here, it should be pointed out that this device is just a prototype to demonstrate the feasibility. The electrodes and device structure can be improved using various methods such as sputtering coating or printing. Figure 4d shows the capacitance results of the fabric device in an ambient environment with different humidity levels. With increasing the relative humidity from 20 to 80%, the capacitance increased linearly in the range of 0.4−1.8 pF. This test was performed on the dry fabric. A larger capacitance was observed when simulated sweat (1% w/v NaCl solution in water) was added into the fabric matrix. As shown in Figure 4e, when the loading of the simulated sweat increased from 20 to 70 g/m2, the capacitance increased almost linearly from 1.66 to 15.24 pF. The change of capacitance caused by sweat loading is almost 10 times larger than that caused by environment humidity. Therefore, the fabric device can be used to measure the content of sweat in the fabric. The above results can be explained by the change of dielectric properties between the two electrodes. For a flat capacitor just filled with air, the capacitance (C) can be described as C=

Q A =ε V d

C = ε0εr

A d

(2)

Here, ε0 is the permittivity for air, and εr is the permittivity for the medium. In our case, there is no change in the device structure except that moisture is added to the fabric matrix. Since salt water has a much larger permittivity than air, the inclusion of salt water largely increases the capacitance. We also tested the effect of temperature on the capacitance. Since this multifunctional fabric was designed for measuring sweat content in fabric, the temperature change should be around the body temperature. Here, the temperature range of 25−45 °C was chosen. As shown in Figure 4f, the capacitance change in this temperature range was less than 0.4 pF, which is far smaller than the change caused by air humidity. Therefore, the temperature change should have very little effect on the detection. We also probe the role of the PPy coating in the sensor device by using a control fabric (without PPy) to make the sensor device. As expected, the device made of the control fabric had a very small capacitance, and it showed almost no response to the loading of simulated sweat (Supporting Information). The much larger response of the PPy fabric device than that of the control fabric can be explained by the effective capacitor formed between the PPy layer and back electrode. Since the metal wires have very small areas, just the metal wires cannot form an effective capacitor. In addition, the PPy-coated fabric showed reasonable durability to repeat wash and abrasion. After standard laundering for 50 cycles, the fabric still maintained the directional water transport feature, with R values of 227% (PPy side) and −71% (back side). After abrasion for 10,000 cycles, the R values almost remained unchanged (Supporting Information). The SEM images indicated that washing led to a very small change in the surface morphology of the PPy coating. For abrasion, the PPy coating on the top surface fibers was partially damaged, but the fibers underneath still maintained an original surface feature (Supporting Informa-

(1)

where Q is the electrical charge, V is the applied voltage, A is the area of the plate electrode, ε is the permittivity of air (e.g., 22882

DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

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ACS Applied Materials & Interfaces

(5) Zhao, Y.; Yu, C.; Lan, H.; Cao, M.; Jiang, L. Improved Interfacial Floatability Of Superhydrophobic/Superhydrophilic Janus Sheet Inspired By Lotus Leaf. Adv. Funct. Mater. 2017, 27, 1701466. (6) 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, 1600276. (7) 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, 1704220. (8) Wang, H.; Wang, X.; Lin, T. Unidirectional Water Transfer Effect From Fabrics Having A Superhydrophobic-To-Hydrophilic Gradient. J. Nanosci. Nanotechnol. 2013, 13, 839−842. (9) 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. (10) Zhang, Y.; Feng, W.-X.; Legrand, Y.-M.; Supuran, C. T.; Su, C.Y.; Barboiu, M. Dynameric Host Frameworks For The Activation Of Lipase Through H-Bond And Interfacial Encapsulation. Chem. Commun. 2016, 52, 13768−13770. (11) Zhang, Y.; Barboiu, M. Dynameric Asymmetric Membranes For Directional Water Transport. Chem. Commun. 2015, 51, 15925− 15927. (12) 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, 1600036. (13) Yang, Y. L.; Lo, L. H.; Huang, I. Y.; Chen, H. J. H.; Huang, W. S.; Huang, S. R. S. Improvement Of Polyimide Capacitive Humidity Sensor By Reactive Ion Etching And Novel Electrode Design. In Sensors; IEEE: 2002, 1, 511−514. (14) Chen, Z.; Lu, C. Humidity Sensors: A Review Of Materials And Mechanisms. Sens. Lett. 2005, 3, 274−295. (15) Saha, D.; Das, S.; Sengupta, K. Development Of Commercial Nanoporous Trace Moisture Sensor Following Sol−Gel Thin Film Technique. Sens. Actuators, B 2008, 128, 383−387. (16) Nybo, L.; Secher, N. H. Cerebral Perturbations Provoked By Prolonged Exercise. Prog. Neurobiol. 2004, 72, 223−261. (17) Nielsen, B.; Nybo, L. Cerebral Changes During Exercise In The Heat. Sports Med. 2003, 33, 1−11. (18) McGuigan, M. Monitoring Training and Performance in Athletes; Human Kinetics: Champaign, 2017. (19) Kaya, T.; Liu, G.; Ho, J.; Yelamarthi, K.; Miller, K.; Edwards, J.; Stannard, A. Wearable Sweat Sensors: Background And Current Trends. Electroanalysis 2019, 31, 411−421. (20) Ataman, C.; Kinkeldei, T.; Vasquez-Quintero, A.; MolinaLopez, F.; Courbat, J.; Cherenack, K.; Briand, D.; Tröster, G.; de Rooij, N. F. Humidity And Temperature Sensors On Plastic Foil For Textile Integration. Procedia Eng. 2011, 25, 136−139. (21) Weremczuk, J.; Tarapata, G.; Jachowicz, R. Humidity Sensor Printed On Textile With Use Of Ink-Jet Technology. Procedia Eng. 2012, 47, 1366−1369. (22) Lin, Q.; Li, Y.; Yang, M. Investigations On The Sensing Mechanism Of Humidity Sensors Based On Electrospun Polymer Nanofibers. Sens. Actuators, B 2012, 171-172, 309−314. (23) Coyle, S.; Lau, K.-T.; Moyna, N.; O’Gorman, D.; Diamond, D.; Di Francesco, F.; Costanzo, D.; Salvo, P.; Trivella, M. G.; De Rossi, D. E.; Taccini, N.; Paradiso, R.; Porchet, J.-A.; Ridolfi, A.; Luprano, J.; Chuzel, C.; Lanier, T.; Revol-Cavalier, F.; Schoumacker, S.; Mourier, V.; Chartier, I.; Convert, R.; De-Moncuit, H.; Bini, C. BiotexBiosensing Textiles For Personalised Healthcare Management. IEEE Trans. Biomed. Eng. 2010, 14, 364−370. (24) Wang, H.; Xue, Y.; Lin, T. One-Step Vapour-Phase Formation Of Patternable, Electrically Conductive, Superamphiphobic Coatings On Fibrous Materials. Soft Matter 2011, 7, 8158−8161. (25) Wang, H.; Zhou, H.; Gestos, A.; Fang, J.; Niu, H.; Ding, J.; Lin, T. Robust, Electro-Conductive, Self-Healing Superamphiphobic Fabric Prepared By One-Step Vapour-Phase Polymerisation Of Poly(3,4-Ethylenedioxythiophene) In The Presence Of Fluorinated Decyl Polyhedral Oligomeric Silsesquioxane And Fluorinated Alkyl Silane. Soft Matter 2013, 9, 277−282.

tion, Figure S9). These indicate the reasonable durability of the PPy coating. It should be pointed out that although here, we used polypyrrole as a model to prepare the multifunctional fabric, other hydrophobic conductive materials should also be suitable for this treatment. Therefore, the approach developed should be general for preparing electrically conductive, directional water transport fabrics and fabric-based capacitive moisture sensors.

4. CONCLUSIONS We have demonstrated that single-side coating of an electrically conductive, hydrophobic material on a hydrophilic fabric can make the fabric have a one-way water transport capability and single-side conductivity. Upon integrating two metal wires, the fabric can form a capacitive sensor to sense sweat in the fabric. The conducting layer enables the sensor device to have a sufficient capacitance response. However, the metal wires have little effect on the directional water transport and fabric breathability. Reasonable integration of the electrodes allows the device to have a minimal effect on fabric handle. This novel, multifunctional, directional water transport fabric may find applications in making “smart” clothing.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b06787.

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Air humidity detection, AFM images, SEM images, XPS spectra, FTIR spectra, photos of water droplets, air permeability, moisture permeability, washing and abrasion durability, and capacitance (PDF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (H.W.). *E-mail: [email protected] (T.L.). ORCID

Tong Lin: 0000-0002-1003-0671 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the funding support from an Australian Research Council Discovery Project (DP 190100306).

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REFERENCES

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DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884

Research Article

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DOI: 10.1021/acsami.9b06787 ACS Appl. Mater. Interfaces 2019, 11, 22878−22884