Dielectric Properties of Wool-Water Systems at 3000 and 9300 Megacycles

Abstract

The dielectric constant ε′ and dielectric loss ε″ for wool‐water systems have been determined at frequencies of 3000 and 9300 Mc by a cavity resonator method. The water content of the wool fibers was varied between 0 and 14 percent of the weight of the dry wool. The upper limit of 14 percent is approximately one‐half the amount of water wool will absorb in a saturated atmosphere at 25°C. The increased dielectric loss in the systems studied and the resultant attenuation of microwave power prevented measurements from being made at water contents in excess of approximately 14 percent. The results of the measurements show that both ε′ and ε″ increase with increasing water content. The results have been analyzed in terms of a sorption theory proposed by Cassie which shows that the water sorbed by wool consists of localized water which is intimately bound to polar sites in the wool and mobile water which constitutes the remainder sorbed. The dielectric constant of the localized water is found to be 5.8 at both frequencies. This result compares favorably with the microwave dielectric constant of irrotationally bound water obtained by Buchanan et al. from studies of protein hydration. It has been found that ε′ and ε″ of the mobile water are less than for liquid water if the dielectric properties of the wool are assumed to be unaffected by water sorption. The alternate assumption (in which ε′ and ε″ for the mobile water are set equal to those of liquid water) is discussed.