The electromechanical response of a polyurethane elastomer was investigated at room temperature and in the temperature range near its glass transition. It was found that the Maxwell stress contribution to the strain response can be significant at temperatures higher than the glass transition temperature. In addition, the material exhibits a very high electrostrictive coefficient Q, about two orders of magnitude higher than that of polyvinylidene fluoride. It was also found that in a polymeric material, the chain segment motions can be divided into those related to the polarization response and those related to the mechanical response and the overlap between the two yields the electromechanical response of the material. In general, the activation energies for different types of motion can be different, resulting in different relaxation times in the dielectric, the elastic compliance, and the electrostrictive data, as observed in the polyurethane elastomer investigated. The experimental results indicate that at the temperatures investigated, the activation energy for the mechanical related segment motions is higher than that of nonmechanical related segment motions.

ABSTRACT:The electromechanical properties of a segmented polyurethane elastomer were investigated as functions of temperature and frequency. Two transitional phenomena were observed in the temperature range from 050 to 85ЊC. In these transition regions, the electric field induced strain coefficient exhibits large increases, which indicate that the effect of the transition processes is significant. The experimental analysis suggests that the transitional processes in the polyurethane are related to the chainsegment motions. From the elastic compliance and the dielectric constant data, the contribution of the uniform Maxwell stress was determined. It was found that the contribution of the Maxwell stress effect to the measured strain coefficient increased from about 10% below the glass transition temperature (T g ) (Ç 025ЊC) to about 50 and 35% for the frequencies of 10 and 100 Hz, respectively, at Ç 40ЊC, which is above T g . The large difference between the measured strain response and the calculated Maxwell stress effect indicates a significant contribution to the field-induced strain from other mechanisms, such as electrostriction.

Some aspects of the engineering applications of elastomeric materials in sonar transducers are discussed. A sonar materials handbook being published as NRL Memorandum Report 4311 is also briefly reviewed.

The absorption and emission spectra of quinizarin (1,4-dihydroxy-anthraquinone) have been investigated in hydrocarbon and alcoholic solvents. Fluorescence spectra in 3 different Shpolskii matrices were recorded at 14 K. Vibrational analyses of these spectra revealed the presence of 3, 8, and 9 sites in octane. heptane, and hexane matrices, respectively. The fluorescence lifetime was found to be 6.5 ns in hexane and EPA. Fluorescence photoselection measurements in EPA (77 K) showed that the first 4 electronic transitions of quinizarin are polarized parallel, parallel. perpendicular, and parallel to the long molecular axis and can be assigned, in order of increasing energy. to 'BZ, 'B2. 'A, and 'Bz (rrn*) + 'A,!C2v) trmsitions. respectively. The fluorescent transition is assigned as 'Bz(nn*)+ 'Al. The absence of phosphorescence is attributed to the intramolecular hydrogen bonding present which displaces the parent anthraquinone nn* states above the nn* states, thereby rendering the intersystem crossing (S,-T,) radiationless pathway inefficient.Photoselection measurements on daunorubicin, a substituted quinizarin and known anticancer drug, revealed an absorption band polarization pattern identical to that of quinizarin. These results are in part at variance with assumptions used in previous work on the intercalation specificity of daunorubicin with DNA.

The effects of carbon black type and loading, and variation of base polymer, on a series of polychloroprene rubbers {neoprenes} have been investigated. Two common types of neoprenes, each with a lead oxide cure system, were used. The acoustic responses of these materials were characterized for extensional wave propagation in air by a resonance technique and longitudinal wave propagation in water through the use of a high-frequency sing-around device and an underwater acoustic impedance tube. The viscoelastic properties of neoprene elastomers were found to be strongly influenced by both the degree of loading and average particle size of the carbon black used. The results are discussed in terms of mechanisms of interaction between the carbon black filler and the gum phase of the elastomer.