Interplay between bulk and molecular viscosity of a soft glassy nematic gel

ABSTRACT

We report on the interplay between viscosity at bulk and molecular levels in a nematic liquid crystal gel. Concentration dependence of the thermal, visco-elastic, and electro-optic properties is studied extensively on a composite prepared from a nematic liquid crystal host and a simple organogelator. The calorimetric and rheological measurements distinguish between four different states depending on the gelator concentration in the composite: (i) the flocculated fluid, where the nematic host and gelator molecules coexist without gel fibre formation; (ii) entangled solid, where the gel fibres exist as entangled aggregates without network formation; (iii) weak gel, which is a structured fluid and (iv) strong gel, with cross-linked gel network confining the host nematic. The electro-optic studies indicate that the rotational viscosity reduces by an order of magnitude in the weak gel compared to the pure nematic. Interestingly, the bulk viscosity gets enhanced, also by the same factor as observed from rheological studies. In addition to faster response times, the undesirable backflow effect, typically observed for nematic liquid crystals, is absent in the weak gel. Thus, the enhanced mechanical strength and electro-optic parameters make the weak gel preferred for LC display and switching devices.

Graphical Abstract

short-legendThe weak nematic gel system with its enhanced bulk viscosity and reduced rotational viscosity is highly desirable for robust display devices.

KEYWORDS:

• Organogel
• nematic liquid crystal
• viscosity
• structural relaxation
• electro-optic response

Acknowledgments

GGN is thankful for the grant (No. SR/S2/CMP-21/2011) received from SERC, Department of Science and Technology (DST), New Delhi, India.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was supported by the SERC, Department of Science and Technology (DST), New Delhi, India [SR/S2/CMP-21/2011].