Abstract
We explore the optical birefringence of the nematic binary mixtures () embedded into parallel-aligned nanochannels of mesoporous alumina and silica membranes for channel radii of nm. The results are compared with the bulk behavior and analyzed with a Landau–de Gennes model. Depending on the channel radius the nematic ordering in the cylindrical nanochannels evolves either discontinuously (subcritical regime, nematic ordering field ) or continuously (overcritical regime, ), but in both cases with a characteristic paranematic precursor behavior. The strength of the ordering field, imposed by the channel walls, and the magnitude of quenched disorder varies linearly with the mole fraction and scales inversely proportionally with for channel radii larger than 4 nm. The critical pore radius, , separating a continuous from a discontinuous paranematic-to-nematic evolution varies linearly with and differs negligibly between the silica and alumina membranes. We find no hints of preferred adsorption of one species at the channels walls. By contrast, a linear variation of the nematic-to-paranematic transition point and of the nematic ordering field versus suggests that the binary mixtures of cyanobiphenyls 6CB and 7CB keep their homogeneous bulk stoichiometry also in nanoconfinement, at least for channel diameters larger than 7 nm.
2 More- Received 4 January 2014
DOI:https://doi.org/10.1103/PhysRevE.89.062501
©2014 American Physical Society