Fluctuations above the Smectic-A-Isotropic Transition in Liquid Crystalline Elastomers under External Stress

Abstract

Using birefringence measurements, we observe for the f i s t time nematic as well as smectic fluctuations above the smectic-A-isotropic transition in liquid crystalline elastomers under an external mechanical stress. From a mean-field analysis we f i d that there are temperatures (far above the isotropic-A transition) for which nematic fluctuations dominate as well as a range of temperatures (above and close to this phase transition) where smectic fluctuations are more important. These two regimes are connected by a crossover regime where the coupling between the two types of fluctuations becomes important. We also discuss the possibility of a triple point in liquid crystalline elastomers, where an isotropic, a smectic and a nematic phase meet.

A Smectic A Liquid Single Crystal Elastomer (LSCE): Phase Behavior and Mechanical Anisotropy

“…For the latter the induced birefringence is smaller roughly by a factor of two. [14] Most interestingly we find a non-linear behavior of Dn (T). Within the meanfield model we expect the linear relation 1/Dn V S -1 V (T-T*) -c (where T* is the hypothetical phase transformation temperature and c is the critical exponent) with the critical exponent c = 1.…”

“…This orientation process of the network was assumed to be guided by nematic and/or smectic fluctuations [14] in the isotropic pretransformational region, which is already ordered by the chemically locked-in network anisotropy. [1] At the phase transformation these ordered structures might act as nucleation centers for the formation of a uniform phase structure.…”

Existence of Two Different Isotropic Phases as a Reason for Bistable Phase Behavior of an LC Side‐Chain Polymethacrylate

“…For the same reason, the kink cannot be explained by smectic fluctuations, in contrast to the non-monotonous but smooth Dn E (T) dependence reported for an LC elastomer. [20] We should rather suggest certain changes in the near-range order and/or in the molecular packing of mesogenic groups at a phase transition between two different isotropic phases, IsoA and IsoB, at the T ii point. That should be a second order transition, since DSC data show no peculiarities within the temperature range of 65-80 8C.…”

Short-Range Order Fluctuation in the Isotropic Phase of Solutions of 4-trans-4'-n-dodecylcyanobiphenyl in Benzene Studied by Nonlinear Dielectric Spectroscopy

“…Recently, the direct transition from the isotropic phase to the one of smectic phases has attracted a lot of attention [16][17][18][19][20][21]. The Kerr effect studies [16], X-ray reflectivity measurements on the free surface of 4-trans-4 -n-dodecylcyanobiphenyl (12CB) [17], the strain birefringence measurements [18], and dielectric studies [19] show that the isotropic-smectic A type (I-SmA) transition is more strong first order than the I-N transition, which is known to be a very weak first order transition.…”

“…The Kerr effect studies [16], X-ray reflectivity measurements on the free surface of 4-trans-4 -n-dodecylcyanobiphenyl (12CB) [17], the strain birefringence measurements [18], and dielectric studies [19] show that the isotropic-smectic A type (I-SmA) transition is more strong first order than the I-N transition, which is known to be a very weak first order transition. The low-angle X-ray measurements [17] have detected the existence of smectic A type cybotactic groups in the isotropic phase.…”