Thursday, 21 March 2019

Bent-core structures between polymer strands

P. Lakshmi Madhuri, Uma S. Hiremath, C.V. Yelamaggad, K. Priya Madhuri and S. Krishna Prasad, Phys. Rev. E 93, 042706 (2016)

Effect of a polymer network on the threshold voltage of the Freedericksz transition, Frank elastic constants, switching speed and the rotational viscosity is investigated in a polymer-stabilized bent-core nematic liquid crystal (PSBLC) with different polymer concentrations. These polymer networks form virtual surfaces with a finite anchoring energy. The studies bring out several differences in comparison to similar studies with a calamitic liquid crystal as the nematic host. For example, on varying the polymer content the threshold voltage decreases initially but exhibits a drastic increase above a critical concentration. A similar feature – reaching a minimum before rising – is seen for the bend elastic constant, which gets enhanced by an order of magnitude for a polymer content of 2.5 weight%. In contrast, the splay elastic constant has a monotonic variation although the overall enhancement is comparable to that of the bend elastic constant. The behaviour changing at a critical concentration is also seen in the switching time and the associated rotational viscosity. The presence of the polymer also induces a shape change in the thermal dependence of the bend elastic constant.   We explain the new features observed here on the basis of images obtained from the optical and atomic force microscopy.

Posted by S. Krishna Prasad