As. Sailaja et al., ROTATIONAL VISCOSITY (GAMMA(1)) STUDY OF NEMATIC PHASES IN BINARY-LIQUID CRYSTAL MIXTURES OF 6OCB AND 8OCB, Molecular crystals and liquid crystals science and technology. Section A, Molecular crystals and liquid crystals, 250, 1994, pp. 177-183
Rotational viscosity coefficient is measured in different nematic phas
es of a binary liquid crystal system 6OCB-8OCB, as a function of relat
ive concentration of the constituents, and of temperature at each conc
entration, using a transient NMR technique. Experiments are performed
on four such mixtures with relative concentrations chosen such that fo
r two of them there is a re-entrant nematic phase with an intervening
smectic A phase (high temperature (HN) and re-entrant (RN) nematic pha
ses), whereas for the other two there is only a single nematic phase (
SN). Variation of gamma(1) with concentration and temperature is disti
nct in the HN and RN phases, while the corresponding behaviour in the
SN phase is qualitatively the same as that in the RN phase. The variat
ion of activation energies in all the phases as a function of the rela
tive concentration further confirms this observation. It is suggested
that the dynamics in HN phase is influenced by the smectic order fluct
uations remnant in the system due to the underlying smectic phase, and
hence is dynamically different from the SN and RN phases, which are o
btained by direct melting of the solid.