Textiles capillary effects

One important lesson is that measurement of the apparent contact angle of a sessile drop will not give a true measure of the wettability - or even surface free energy - of the fiber surface. The apparent contact angle will always be affected by microscopic surface property (i.e. fiber surface), macroscopic surface geometry (fabric), and capillary effects. In case of hydrophilic substrates the sessile droplet will penetrate the porous textile, typically in seconds, and thus effectively prohibit the measurement. On a hydrophobic surface, the apparent contact angle will always differ from the true contact angle on the fiber surface. Capillary effects occur even on hydrophobic substrates and compete with evaporation of the liquid. 

The coupled heat and liquid moisture transport of nano-porous material has wide industrial applications in textile engineering and functional design of apparel products. Heat transfer mechanisms in nano-porous textiles include conduction by the solid material of fibers, conduction by intervening air, radiation, and convection. Meanwhile, liquid and moisture transfer mechanisms include vapor diffusion in the void space and moisture sorption by the fiber, evaporation, and capillary effects. Water vapor moves through textiles as a result of water vapor concentration differences. Fibers absorb water vapor due to their internal chemical compositions and structures. The flow of liquid moisture through the textiles is caused by flber-liquid molecular attraction at the surface of fiber materials, which is determined mainly by surface tension and effective capillary pore distribution and pathways. Evaporation and/or condensation take place, depending on the temperature and moisture distributions. The heat transfer process is coupled with the moisture transfer processes with phase changes such as moisture sorption and evaporation. 

The main influencing factors are the chemical and physical structure of the fiber material and the design of the textile (for example, capillary effects). Also, finishing processes can play a part. 

Another surface functionalization enhancement created by thin film deposition pertains to the wickability. Textile wickability depends primarily on the capillary effect along and between textile fibers. This property is leveraged today with apparel which rapidly transports sweat from the body. Atmospheric pressure plasma polymerization can increase the hydrophilicity at the fiber surface. Critical to this purpose is the sufficient diffusion of precursor-rich plasma species between and around the filaments. Plasma parameters such as power density and gas/pre-cursor introduction rate will influence the efficiency of the surface activation and deposition. Ultimately, there is an optimal power density and precursor introduction rate which will meet the practical processing requirements of the textile. Likewise, penetration of the active plasma/precursor species will be dependent... 

Physical and ionic adsorption may be either monolayer or multilayer (12). Capillary stmctures in which the diameters of the capillaries are small, ie, one to two molecular diameters, exhibit a marked hysteresis effect on desorption. Sorbed surfactant solutes do not necessarily cover ah. of a sohd iaterface and their presence does not preclude adsorption of solvent molecules. The strength of surfactant sorption generally foUows the order cationic > anionic > nonionic. Surfaces to which this rule apphes include metals, glass, plastics, textiles (13), paper, and many minerals. The pH is an important modifying factor in the adsorption of all ionic surfactants but especially for amphoteric surfactants which are least soluble at their isoelectric point. The speed and degree of adsorption are increased by the presence of dissolved inorganic salts in surfactant solutions (14). 

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