Acoustic characterization of ultrasonic transducer materials II. The effect of curing agent in binary epoxy blends on acoustic properties

The acoustic properties of seven new series of binary epoxy blends as a fun ction of the composition of the flexible epoxy were studied at room tempera ture in the low-MHz frequency range. Each blend was composed of a flexible epoxy resin, DER 736, mixed with one of four rigid epoxies, DER 330, DER 33 1, DER 332 or DEN 431, and crosslinked with one of four curing agents, DEH 26, DEH 29, DEH 39 or Thermoset 310. All elastic moduli and Poisson's ratio s were calculated by using longitudinal velocity, shear velocity and densit y. This paper focuses on the effect of curing agents on the epoxy blends th roughout the entire range of epoxy mix ratios. It has been found that there are basically two types of acoustic properties in these formulations depen ding on whether their glass transition temperature is above or below the te mperature at which the measurements are made. The acoustic properties were strongly influenced by the curing agent and the amount of DER 736. However, for a given curing agent, the selection of the specific rigid epoxy did no t have a large effect on the properties. (C) 1999 Elsevier Science B.V. All rights reserved.