J. D. Lee
NSWC, Silver Spring, MD 20903-5000
Georgia Inst. of Technol., Atlanta, GA 30332
The electrostriction of polyurethanes of two widely different morphologies were measured by laser Doppler vibrometry (LDV). The typical morphology of a polyurethane is that of two separated phases, one of hard regions embedded in the second of a soft elastic matrix. In contrast to this is a polyurethane of a single homogenous phase (i.e., phase mixed). A postulated mechanism for electrostriction is the relaxation, under electric field, of the elastic matrix which is strained in the phase separated system and not in the phase mixed system. To test this hypothesis, both of these systems were synthesized and their d[sub 33] coupling coefficient was determined from measurements of the out-of-plane displacement. The measured electrostriction coefficient at 250 Hz, for bilayers, for the phase separated system is 0.20 A/V (514 V/mil bias) and for the phase mixed system is 0.55 A/V (316 V/mil bias). The larger value for the phase mixed system is in accord with its modulus being less than that of the phase separated system and not a mechanism due to a prestrained soft segment. Details of sample mounting specific to thin films (1 mil) and sampling statistics for d[sub 33] as measured by LDV will be given.