ELASTIC PROPERTIES OF MAGNETIC SUSPENSIONS IN LYOTROPIC NEMATIC LIQUID-CRYSTALS

A pseudo-molecular model is used to evaluate the elastic constants of a lyotropic nematic liquid crystal in which magnetic particles are sus pended, The effective twist and bend elastic constants are shown to va ry nonmonotonically with the concentration of magnetic grains, As the concentration is increased above a critical value, the twist constants K-22 and K-33 decrease below that of the undoped liquid crystal. This corresponds to the concentration above which the liquid crystal-magne tic grains composite has an effectively ''collective'' behaviour. The origin of the nonmonotonic behaviour is due to the destabilizing contr ibution of the magnetic grain-magnetic grain interaction to the total orientational energy. (C) 1997 Elsevier Science B.V.