Nuclear Magnetic Relaxation and Self Diffusion in a Series ofp-Alkanoyl-Benzylidene-P'-Aminoazobenzenes

Proton Spin Relaxation in Reentrant Nematic Cyano -biphenyl Liquid Crystals

“…the elastic constant (see Table 1). Such an increase of T10F at the nematic to smectic phase transition is known in the literature for several non-reentrant mesogens [34,35], It's observation in the present study at both the ne matic to smectic and the reentrant nematic to smectic transition underlines the close parallels between the collective reorientations in the two nematic states, and thus corroberates our main conclusion. According to (2), the magnitude of the discontinuities depends on the Larmor frequency and numerous material parameters, most of which are not available for a quantitative evaluation.…”

“…The re laxation rate caused by collective molecular reorienta tions, and hence the related amplitudes (;4nem, 4 sm) and cut-off frequencies (vcncm, vcsm), are of the same order of magnitude as measurements available for sev eral non-reentrant nematic or smectic mesophases [18-22, [34][35][36][37], This implies that the relative impor tance of the nematic-type fluctuations on Tx is notably different from that of the smectic-type fluctuations (in Figs. 4 and 5, T10Fncm/T10Fsm% 1/5 for v-*0), whereas the changes of the cut-off frequency or the related time constant are less evident (in Figs.…”

“…Hence to analyse the new reentrant data quantita tively we follow, as far as possible, the concepts devel oped for proton relaxation in nematic liquid crystals [18][19][20][21][22], and then contrast our calculations with pre dictions based on a model with smectic order fluctua tions [34][35][36][37], 3. Discussion…”

“…On the other hand most of the dispersion profiles reported for smectic phases [34][35][36][37], typically a strong increase at low Larmor frequencies followed by a plateau and then by another, yet smaller growth at high Larmor frequencies, have been attributed to a combination of smectic order fluctuations of the direc tor (OFsm. damped modes propagating in the layer planes, T1^-v1) with self-diffusion and anisotropical rotations similar to ncmatics, though some details are less clear.…”

Diffusion studies in confined nematic liquid crystals by MAS PFG NMR

“…Several modifications of the PFG NMR method including nematic and solid echoes [15,21], dipolar decoupling [15,21,22], magicangle sample orientation [15,23], and a combination of multipulse dipolar decoupling in addition to the stimulated echo [17,24] were suggested to overcome the above-mentioned difficulties. The most accurate value of the diffusion coefficient in liquid crystals was obtained by using a gradient slice selection, stimulated echoes and a multipulse homonuclear decoupling [16,17,25].…”