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Electrorheological (ER) and dielectric properties under high electric fields were measured simultaneously on hydroxypropylcellulose suspension. When measuring these properties as a function of frequency of the electric field, we found a positive peak in each spectrum of the ER effect and the first-order dielectric permittivity while a negative one in the spectrum of the third-order dielectric permittivity with these peak frequencies nearly equal to (shear rate)/4pi . Referring to the well-known results for the particle rotation in the sheared suspension, it is suggested that the observed peaks are due to shear-induced particle rotation and the rotation occurs even under high electric field. On the basis of these results, effects of the particle rotation on the ER and the dielectric properties are discussed.

Time-resolved resonance Raman and surface-enhanced resonance Raman scattering (RRS and SERRS) spectra were measured for the monocation radical of heptylviologen (HV'+) formed on a silver electrode surface as a function of time ( t ) after switching the electrode potential from -0.2 V (vs Ag/AgCl) to -0.65 V (the monocation radical formation potential). The intensity of the R R S band at 1530 cm-I due to HV'+ increases as a linear function of t 3 / 2 in the first step (0 to ca. 4 ms) and as a linear function of t l / * in the second (4-10 ms) and third steps (10-30 ms). The t312-dependence indicates an instantaneous nucleation mechanism, which consists of instantaneous formation of a nucleus and subsequent three-dimensional growth of the nuclei, and the t'i2-dependence indicates one-dimensional diffusion-controlled film growth processes. Measurement of transient currents confirmed the existence of the two kinds of one-dimensional diffusion-controlled film growth processes. Time-resolved SERRS spectral measurements proved that the monocation radical formation process in a few monolayers of the HV2+ molecules adsorbed at a roughened silver electrode surface proceeds following a mechanism similar to that of the first step observed for the smooth silver electrode surface. The time-resolved R R S and SERRS spectra indicated that at the beginning of the reduction process the radicals exist as a dimeric state at both the smooth and roughened silver electrode surfaces and that the conversion from the dimer to a radical salt begins when the radicals form a film of a thickness of at least 5 monolayers.