Chemical structure of GSC98. The material exhibits an oblique columnar mesophase upon melting (Ref. 20).
(Color online) (a) Strain amplitude versus storage (G′) and loss (G″) elastic modulii of E7G at 25 °C exhibiting the linear viscoelastic regime (LVR). G′ is an order of magnitude higher than G″ confirming the elastic behavior expected of a gel. (b) Thermal variation of G′ and G″ of E7G measured in the LVR. At low temperatures G′ is higher than G″ and at 43.5 °C both G′ and G″ decrease by 2–3 orders of magnitude indicating a transition to sol phase.
(Color online) The heating (upper curve) and cooling (lower curve) DSC thermograms at 5 °C/min rate for E7G displaying strong peaks for the LC-sol to isotropic transition but no change across the LC-gel to LC-sol transition.
(Color online) Dependence of dielectric constant on the applied voltage in the LC-gel (25 °C) and LC-sol (53 °C) states of E7G. Both the states show a very clear threshold behavior, with the threshold voltages (Vth) indicated by dashed lines. The inset shows the voltage-sweep carried out in the LC-gel state over a larger voltage-range to achieve a limiting-value behavior.
(Color online) Thermal dependence of (a) Vth and (b) the two principle dielectric constants for E7G. A significant deviation in Vth, and a very weak anomaly in ε|| data [inset to (b)] are seen at the LC-gel to LC-sol transition. The LC-gel to LC-sol and LC-sol to Isotropic (Tiso) phase transitions of E7G are indicated by upward and downward arrows, respectively.
(Color online) Temperature variation of (a) K1 and (b) K3 across LC-gel to LC-sol transition of E7G. Whereas K1 increases by a factor of 5 from LC-sol to LC-gel phase, K3 has a dramatic enhancement by more than two orders of magnitude. For comparison, K1 and K3 values obtained for the host LC, E7 are shown as asterisks in (a) and (b). The LC-gel to LC-sol and LC-sol to Isotropic (Tiso) phase transitions of E7G are indicated by upward and downward arrows respectively. The lines through data points are merely a guide to eye.
(Color online) The dependence of the magnitude of K1, K3 and K3/K1 on the gelator concentration X (weight percentage of GSC98 in E7) in the LC-gel state (25 °C) are shown in (a), (b), and (c), respectively. The two elastic constants as well as their ratio have a systematic, but nonlinear dependence on X.
(Color online) (a) Switch off response profiles in LC-gel and LC-sol states of E7G. The backflow effect, seen in the sol case, and commonly observed in neat nematic films, is absent in the LC-gel state. (b) Electro-optic (EO) response times for the on (τON) as well as the off (τOFF) states when the voltage (1 kHz sine, 76 VRMS) is applied and subsequently removed.
(Color online) A schematic view of the LC gel structure to explain the suggestion that the relative ease with which forming and breaking of the cross-linking gelator strands (thick lines) enclosing the LC molecules (small ellipses) takes place resulting in modest increase of K1, upon an imposed splay deformation (b) from the equilibrium structure (a). In contrast, difficulty in bending the strands drastically increases the K3 value.
The threshold voltage (Vth), the splay and bend elastic constants (K1 and K3), the rotational viscosity (ηr) and dynamic bulk viscosity (η*) in the LC-gel and LC-sol states of sample E7G are compared with the values obtained for NLC, E7.
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