Slow dynamics of thin nematic films in the presence of adsorbed nanoparticles.

Recent experiments indicate that liquid crystals can be used to optically report the presence of biomolecules adsorbed at solid surfaces. In this work, numerical simulations are used to investigate the effects of biological molecules, modeled as spherical particles, on the structure and dynamics of nematic ordering. In the absence of adsorbed particles, a nematic in contact with a substrate adopts a uniform orientational order, imposed by the boundary conditions at this surface. It is found that the relaxation to this uniform state is slowed down by the presence of a small number of adsorbed particles. However, beyond a critical concentration of adsorbed particles, the liquid crystal ceases to exhibit uniform orientational order at long times. At this concentration, the domain growth is characterized by a first regime where the average nematic domain size L_D obeys the scaling law L_D(t)∼t^1/2; at long times, a slow dynamics regime is attained for which L_D tends to a finite value corresponding to a metastable state with a disordered texture. The results of simulations are consistent with experimental observations.© 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]