Surface conductivities, moisture effects

For powders and granular solids, there are two types of antistatic agents surface- and volume-active additives. Surface-active agents, which increase the surface conductivity of individual particles, are effective because triboelectric charge is always situated on the surfaces of individual particles. Most if not all surface-active agents are hygroscopic and thus attract a thin film of water to the surface it is this moisture that is responsible forthe increased surface conduction (van Drumpt, 1991). The effective bulk resistivity of the particles % -may be estimated by assuming that the particles are spherical and of radius R (Jones, 1995). 

It is well known (see Section 10) that surface-adsorbed layers of different substances may change the molecular interaction. Although adsorbed layers do not have any great effect on the electrical forces created at the expense of double-layer charge (see Section 15), nevertheless, if these layers make the surface conductive, we may expect a decrease in Coulomb interaction as time elapses (see Section 16). Moisture on the surface promotes capillary condensation in the gap between the contiguous bodies (see Section 17). 

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. 

See 2-3.1. Electrical conduction through solids takes place both through the bulk material and over the surface. In most cases surfaces have different physical and chemical properties than the bulk, for example due to contamination or moisture. Volume and surface resistivity can be separately measured for solid materials such as antistatic plastic sheet. Powders represent a special case since although both surface and bulk conduction occur, their contributions cannot be individually measured and the volume or bulk resistivity of a powder includes surface effects. 

In addition to direct effects on the plant, benzylamine may induce hydrophobic (water repellent) conditions in soil (Figure 4)-These data indicate a linear increase in moisture content as benzylamine content increases, attributable to the development of a lower unsaturated hydraulic conductivity in the surface soil, which thus became less able to transfer water from depth in response to evaporative demand. McGhie (50) suggests that poor germination of crop and pasture plants may be related to the development of hydrophobic conditions, the affected soil being unable to supply water to the germinating seed. 

Blichmann, C.W., Serup, J., and Winther, A. Effects of single application of a moisturizer evaporation of emulsion water, skin surface temperature, electrical conductance, electrical capacitance, and skin surface (emulsion) lipids. Acta Derm.. Venereol. 1989 69 327-30. 

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