Acoustic analysis of composite soft materials. I. Characterization of the core and boundary layer from compressibility of core/shell particles dispersed in poly(vinyl chloride)

The sound velocity of butyl acrylate rubber particles modified by poly(meth yl methacrylate) in poly(vinyl chloride) was measured as a function of part icle concentration. A model for estimating the adiabatic compressibility of the particle and the boundary layer was proposed. From the model, the part ial specific adiabatic compressibility of the particles and the rubber core were evaluated. The adiabatic compressibility of the rubber core was estim ated as 3.82 x 10(-10) Pa-1. The adiabatic compressibility of the poly(meth yl methacrylate) shell is discussed based on the modified model. The study indicates that the shell, including the boundary layer between butyl rubber and poly(methyl methacrylate), is perturbed by the butyl acrylate molecule s and is so soft as to be comparable to the rubber. (C) 2001 John Wiley & S ons, Inc.