The human body's ability to regulate temperature is critical for adapting to temperature changes in the environment. Thanks to adaptive IR reflectivity, the surface temperature of SMP textiles on a hob is successfully managed in the IR images and the degree of thermal insulation is controlled by 65.7% of the original value. In addition, the shape of the SMP textile, which can be applied to remove sweat from human skin, can be used to enable or disable the targeted transport of water droplets.
Deformation at a temperature above the melting temperature (Tm) of PCL. b) Shape memory behavior of the SMP. 26 Figure 3.4 Raman mapping images of the cross-section of the shape memory polymer (SMP) fiber. 34 Figure 3.13 Mechanism of IR and water permeable properties of the SMP textile. for the AgNW layer at different stretching strain ratios.
AS is the area of SMP fiber spacing, and AT is the total area of SMP textile. Photograph and (b) IR image of human skin after attaching SMP textile and cotton to a water droplet on human skin. IR images at (c) 60 s and (d) 90 s after separation of SMP textile and cotton from human skin.
40 Figure 3.20 Side view images of water transport test of (a) SMP textile (bottom: bare side; top: AgNW side) and (b) cotton fabric.
Introduction
- Stimuli-responsive materials
- Homeostasis and temperature control
- Smart textiles
- Shape memory polymers
- Micro/nanoporous structure
- Aim of study
These stimuli-responsive materials can be applied to various fields, such as biomaterials, actuators and wearable sensors (Figure 1.2).2-5 The material adjusts its shape, chemical structure or mechanical properties in response to these stimulations. For example, textiles made from porous silk (Figure 1.3a)11 or Kevlar fibers (Figure 1.3b)12 show outstanding thermal insulation performance. A Janus hydrophilic/hydrophobic fabric (Figure or cotton fabric with selective plasma treatment,15 can control liquid penetration through the textiles in a directionally controlled manner (Figure 1.5).16 However, these investigations showed no response to external stimuli; static thermal insulation and surface wettability showed.
A regular array of micropores is drilled into a Janus PE/NC textile by laser drilling, then the drilled textile is modified by plasma (Dai, B. Figure 1.5 A porous membrane with superhydrophilicity–hydrophilicity for unidirectional liquid permeation. Development of smart stimuli-responsive textiles have been developed water transport or thermal insulation properties.Wool knitted fabric demonstrated water-responsive thermoregulation by opening and closing pores in the water-responsive knitted fabric (Figure 1.6);17 Graphene-coated fabric with voltage-responsive IR emissive modulated IR transmission (Figure 1.7); 18.
The infrared emissivity of the device is modulated by applying a voltage difference between the top graphene layer and the back electrode layer to initiate the intercalation of ions into the graphene layers. The device is placed on a hot plate at 55 °C. c) Temporal change in the apparent temperature of the device after application of 4 V. d) Long-term temporal variation in the apparent temperature under a periodic square voltage waveform (−2 and 4 V) with a period of 20 s (Ergoktas, M As one of the polymeric stimuli-responsive materials, shape memory polymers (SMPs) have attracted attention in recent decades.
A high temperature can make the molecular chain move more easily, lower the energy barrier and increase the polymer's entropy, making it easier to control. 20 . silver, aluminum, copper, etc.) coating on one side of the textile, elastomer or electrode substrate can provide thermoregulatory SMP textiles with asymmetric wettability and adaptive IR camouflage.37-41. Developing a porous structure is one of the effective ways to improve the responsive performance.
Appropriate shapes of micro/nanostructure responsive polymers can be applied to fabricate smart wearable devices depending on the structure of the actuators and sensors. To adjust the asymmetric wettability, silver nanowires (AgNWs) were also coated asymmetrically on one side of the fabric. The high IR reflection of the AgNW layer combined with the high porosity of the SMP fibers provide excellent thermal insulation.
The porous SMP textile exhibits excellent retention of IR reflectivity and wettability due to its shape memory property, enabling stimuli-responsive thermal insulation and directional water transport. In terms of the temperature difference between the heating plate and the surface of SMP textiles as the.
Experiments
- Materials
- Fabrication of porous SMP fibers
- Fabrication of porous SMP textiles
- Deformation of porous SMP textiles
- Characterization
The resulting SMP textiles had electrical resistances of approximately 15‒25 Ω when measured using a multimeter (3201, Müller). Stretch deformation of porous SMP textiles was performed by stretching the textile unidirectionally at 80 °C, cooling it to room temperature, and releasing the stretching force. Compressive deformation of porous SMP textiles was performed by applying pressure on an 80 °C hot plate.
The deformed textile was cooled to room temperature while maintaining the external force; therefore, the deformed shape was fixed until the textile was reheated above the glass transition temperature of PLA, ~55 °C. The water contact angle of the porous SMP textile was measured using a portable microscope (HA010, GASWORLD, South Korea). The cryofractured cross-section of the porous SMP fibers was observed using a scanning electron microscope (S-4800, Hitachi, Japan).
The Raman spectra and mapping images were obtained using Raman spectroscopy (alpha300R, WITec, Germany) with 532 nm laser excitation. For the Raman spectra, the integration time was 1 s, and the number of accumulations was 20, while the laser power was 1 mW. The elastic modulus of the porous SMP fibers was measured using a tensile tester (TXA-TM, Yeonjin Corp., South Korea).
Human skin surface temperature was measured using a contact thermometer (TM-747D, TENMARS, Taiwan).
Results and Discussion
- Hierarchical micro/nanoporous SMP textile
- Modulation of the thermal insulation by stretching and compressing
- Modulation of the surface wettability by stretching and compressing
- Mechanism of IR- and water-gating properties of the SMP textile
- Applications of IR- and water-gating textiles
And the AgNWs were sprayed uniformly on one side of the SMP textile. The thermal insulation and surface wettability of the SMP textiles can be modulated when deformed under mechanical stretching and compressive stimuli at temperatures above the PLA transition temperature (55 °C). The shape deformation and recovery of the SMP textile can be used to control the direction of water transport.
This significantly reduced the hydrophilicity of AgNW side, with the increase of the water contact angle on the AgNW side (Figure 9). Meanwhile, as shown in Figure 10 , the interfiber gaps were also reduced when the SMP textile was compressed, but there was no observable change in the hydrophilicity of the AgNW side. Similarly, during compressive deformation of the SMP textile at 245 kPa, the directional water transformation was blocked (Figure 11a).
Moreover, because the shape deformation and recovery of the SMP textile are highly reversible, the directional water transport can be repeatedly inhibited and recovered by deformation and recovery by stretching/compression (Figure 11b-c). The mechanism of the tunable IR and water gating processes in the SMP textile is shown in Figure 12. The stretching deformation induced the formation of the crack in the AgNW layer on the SMP fibers parallel to the deformation direction.
In addition, the surface hydrophilicity of the AgNW side was reduced due to the expansion of the exposed polymer region, which prevented directional water transport. From the SEM images of the SMP fibers parallel to the stretching direction, as shown in Figure 8, the ratio of the torn area was measured. After compressive deformation, the AS/AT value decreased from 6.6% to 2.6%, which improved the thermal insulation of the compressed SMP textile.
A schematic illustration of the SMP textile and the SEM images of the AgNW layer on the SMP fibers in each condition were shown in Figure 14. It shows the formation of cracks in the AgNW layer as a result of stretching the SMP fibers up to 50% and 100% (Figure 14a-c). Similarly, Fig. 17a shows IR images for a remote SMP textile recovery test using hot water droplets.
Shape recovery occurred as a result of the direct heat transfer from the hot water (about 70 °C) to the deformed SMP textile, but the shape recovery did not occur with cold water (Figure 16e). It is also indicated by IR images of the human skin after water removal using SMP textiles and cotton (Figure 19).
Conclusion
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