Measurement of the splay-bend elastic constant in lyotropic ferronematic liquid crystals: The influence of the bounding surfaces

Abstract

We report the first experimental investigation devoted to analyze the influence of a ferrofluid on the surface properties of lyotropic liquid crystals doped with magnetic particles. By means of optical methods, the bulk orientation of the director vs the temperature is determined. The theoretical analysis shows that near the nematic–isotropic transition, the thermodynamical model for the temperature surface transition works reasonably well. On the contrary, in the low temperature region near the lamellar–nematic transition, important deviations from the theoretical behavior are observed. In order to interpret our experimental data, we propose a simple phenomenological extension of the thermodynamical model that takes into account the different contributions to the surface energy and of the residual lamellar order in the nematic phase. We show, furthermore, that the effective splay-bend elastic constant depends on the ferrofluid doping concentration, in agreement with a recently proposed theory.

Macroscopic dynamics of ferronematics

“…[6][7][8][9] Particularly appropriate for experimental studies is a lyotropic micellar nematic system 3,10,11 doped with an aqueous ferrofluid. 12,13 The feature of liquid crystal transparency is an issue of considerable interest. 14 Recently highly transparent lyotropic ferrofluid nematic liquid crystals have been reported.…”

Ferrofluids: properties and applications

“…The controversial subject of the effective splay-bend elastic constant, k 13 , was also investigated using ferrofluid doped lyotropic samples [66]. The ratio between k 13 and the usual Frank elastic constant found in the potassium laurate/decanol/water lyotropic mixture was positive and of the order of 1 [67].…”

Hydrodynamics of nematic ferrofluids

“…Starting with the first report in 1970 of mixing magnetic grains with the nematic phase of MBBA [2], there was a number of reports on the production of mixtures of rod-like and disk-like nematics with magnetic grains [2][3][4][5]. Recently, however, the preparation of stable ferronematic systems has attracted increasing attention [7][8][9][10][11][12][13][14][15]. In many systems investigated there were problems with chemical stability.…”