| Due to the special nature of outdoor sports,the evaporation of sweat in changeable weather is a direct threat to human health.If clothing does not keep the body surface dry in time,it can lead to a cold feeling of human body,and even serious safety incidents such as cold stress,frostbite and hypothermia.And the evaporation of sweat from the surface of clothing also indirectly causes significant energy loss.This thesis explores the theory of water transport in trees and the mechanism of foliar wettability regulation of plants in response to environmental changes,thus expanding the theory of water transport and evaporation in natural plants.Inspired by this,a fibrous membrane design-oriented strategy of fast unidirectional sweat transport driven by a stepless gradient of wettability and synergistic effect of sweat evaporation with low heat loss was proposed to enhance sweat transport rate and reduce body heat loss.Firstly,qualitative FT-IR analysis and quantitative delignification tests revealed that the lignin content in the growth direction of the camphor tree gradually increases and the wettability of the cross-section deteriorates.It was concluded that trees have gradual compositional differences in the height direction and trigger gradual wettability to drive water transport,thus extending the traditionally perceived theory of trunk pore gradient driven fluid transport.Inspired by this,polyvinyl alcohol（PVA）nanofibre membranes were prepared by a simple process of heat treatment and coating permeation to produce a stepless wettability gradient polyvinyl acetal（swg-PVF）nanofibre membrane.The differences in the properties of swg-PVF at different thickness positions and their relationship with the wettability variation were investigated.The results showed that the difference in pore size in the thickness direction of swg-PVF was not significant（all around 0.25μm）.With the penetration of formaldehyde reaction solution,the degree of acetal reduction in the thickness direction of swg-PVF gradually decreased from 78.24%to 31.42%;and the wettability gradually increased,with the contact angle decreasing from 106.0°to 33.7°,indicating that swg-PVF relies on stepless wettability gradient to drive the accelerated transport of sweat.Secondly,the effect of the number of steps of the wettability gradient on the transport rate was investigated by theoretical calculations and physical field simulations using MATLAB and COMSOL software,respectively;the unidirectional water transport performance of swg-PVF enhanced by a stepless wettability gradient was compared with that of a commercial moisture wicking fabric（MW Fabric）.The results show that:within a set fabric thickness of 1000μm,the higher the number of steps,the faster the water transfer rate for the same variation in wettability of the inner and outer layers;compared to a two-step wettability gradient,the transfer rate of the stepless wettability gradient can be increased by25.07%.swg-PVF has a faster perspiration transfer rate than MW Fabric,with 2.1 s and 3.2 s,respectively;sweat forward transport index R of 1269%and 196%,respectively.Compared to MW Fabric,swg-PVF has good resistance to reverse permeation with R（reverse）of-265%and-1219%respectively.Finally,by observing the recorded changes in surface fluff morphology and contact angle size of the Conyza canadensis throughout the day,it was found that herbaceous plants such as the Conyza canadensis changed the evaporation morphology of liquid beads by adjusting their leaf surface morphology to cope with temperature variations.Inspired by this,polyvinylidene fluoride（PVDF）nanofibre membranes and sodium alginate（SA）hydrophilic dots were sequentially laminated onto the hydrophilic outer layer of swg-PVF by electrostatic spinning and electrostatic spraying,respectively,to obtain SA/PVDF/swg-PVF（sps-PVF）nanofiber membranes.The spinning process parameters were optimised to obtain the best hydrophobic PVDF nanofibre membrane（141.3°）.SEM analysis showed that the thickness of the PVDF layer was 5μm,the average diameter of the SA hydrophilic points was 400μm and the distance between the hydrophilic points was 0.5 to 1.5 mm.The results of the FLUENT software simulations show that the evaporation of sweat in the form of beads on the surface of the fabric has a smaller effect on the temperature of the fabric than spreading and evaporating inside the fabric.The results of simulated sweat evaporation performance tests on MW Fabric,swg-PVF and sps-PVF showed that the maximum temperature drop of the simulated skin was8.4°C,5.2°C and 3.8°C with evaporation rates of 0.50 g h-1,0.36 g h-1and 0.28 g h-1,respectively.Theoretical calculations show that the sweat produced per person per day in the form of sweat beads evaporates to reduce heat loss by 1,139 k J.The research in the thesis broadens the design thinking for sports comfort clothing fabrics. |
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