Variation of longitudinal acoustic velocity at gigahertz frequencies with water content in rat-tail tendon fibers.

Abstract

AbstractBrillouin scattering was used to determine the longitudinal acoustic velocity along the axis of collagen fibers as the relative humidity decreased from 95 to 0%. Between 0 and 86%, the velocity decreased linearly at a modest rate. Above 86%, the decrease was steep. The changing mass of the absorbed water accounts for most of the velocity change in the lower humidity range. The remaining deviation is probably due to variation of the elastic coupling between molecules. At low humidity, the adsorbed water is known to be attached to the collagen molecules, whereas the additionally adsorbed water at high humidity has the properties of bulk liquid. The high‐humidity sonic velocity variation is ascribed to the presence of free water. It is possible to identify the five water regimes of Pineri et al. [(1978) Biopolymers 17, 2799–2815] with the variations of the sonic velocity with water content.