Free-standing anisotropic side chain liquid crystalline elastomer films have been prepared
using mesogens with laterally affixed polymerizable side chains. We present data on two networks: one
containing the monomer of 4‘-acryloyloxybutyl 2,5-(4‘-butyloxybenzoyloxy)benzoate and another from a
50/50 mol % mixture of the above with 4‘-acryloyloxybutyl 2,5-di(4‘-pentylcyclohexyloyloxy)benzoate. The
cross-linking was achieved using 10 mol % of 1,6-hexanediol diacrylate. The calculated cross-linking
density, as determined from the Young's modulus, was in the 10 -5 mol/cm3 range. Thermoelastic responses
show strain changes through the nematic−isotropic phase transition to be 30−45%. The order parameters
of the oriented films were determined from the dichroic ratio of IR absorption at 3343 cm-1 to the in-plane aromatic stretching overtone of the LC mesogen core. The variation of the order parameter with
temperature scales similar to the strain changes at constant stress. Isostrain studies, conducted through
the nematic to isotropic phase transition, show that the two networks behave as true elastomers with
significant differences in the force developed. Dynamic shear measurements near the nematic to isotropic
phase transition region show that the mechanical relaxation peak appears above 100 Hz, and that
viscoelastic relaxations are minimal in the nematic to isotropic phase transition region below 5−10 Hz.
Molecular electronics has been proposed as a pathway for high-density nanoelectronic devices. This pathway involves the development of a molecular memory device based on reversible switching of a molecule between two conducting states in response to a trigger, such as an applied voltage. Here we demonstrate that voltage-triggered switching is indeed a molecular phenomenon by carrying out studies on the same molecule using three different experimental configurations-scanning tunnelling microscopy, crossed-wire junction, and magnetic-bead junction. We also demonstrate that voltage-triggered switching is distinctly different from stochastic switching, essentially a transient (time-dependent) phenomenon that is independent of the applied voltage.
We report the synthesis and physical studies of a liquid crystalline elastomer fiber consisting
of two side-chain liquid crystalline acrylates and a nonmesogennic comonomer side group that acts as a
reactive site for cross-linking. The terpolymer was synthesized by radical polymerization, and the cross-linking of the network was achieved by using a diisocyanate unit. The fiber formed shows good liquid
crystal alignment texture under a cross-polarizer microscope. Thermoelastic response shows strain changes
through the nematic−isotropic phase transition of about 30−35%. A retractive force of nearly 300 kPa
was measured in the isotropic phase. Static work loop studies show the viscoelastic losses in these materials
to be very small. We also present preliminary studies on the effect of doping carbon nanotubes on the
induced strain at the nematic−isotropic transition.
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