No abstract

The structure around lithium counterions in polyacrylate solutions has been investigated by neutron diffraction, and it is concluded that small cations remain hydrated when they accumulate around a highly charged polymer. Interactions between the polyion and the counterions over a range outside the hydration shell are also observed. The relaxation rate of 7Li due to dipolar coupling to 17 0 was obtained by nuclear magnetic resonance. The results indicate that the polyion exerts a moderate influence on the reorientational dynamics of the lithium aqua-ion.

The dynamic IR spectra of electrically modulated liquid crystalline 5CB (4-pentyl-4'-cyanobiphenyl) are determined to be due to the director reorientation. In the absence of dc fields, the IR response is mainly at two times the modulation frequency. IR signals at the modulation frequency may be induced by application of additional dc fields. These signals at the modulation frequency are caused by the creation of polar orientation due to the static field. No difference in dynamic response has been found between the rigid aromatic core and the pentyl chain of 5CB. Expressions are given for the in-phase and in-quadrature signals at the modulation frequency and at twice its value. It is shown that the frequency-domain dynamic IR experiment mainly probes the transition range between the uniform planar to the homeotropic regions in the sample. The different probing of the sample by time-domain experiments is briefly discussed.

Attenuated total reflection and transmission results on the electric perturbation of liquid crystalline 5CB between orienting walls are compared. In the interface between a wall and the bulk a depth dependent average orientation of the director is observed in the presence of ac fields. In this transition region the dynamic behaviour of the liquid crystal shows a faster and qualitatively different response from the bulk. Near the orienting wall the effect of the field perpendicular to the wall depends on the field direction as indicated by the observation of a large response component at the ac frequency.