Phase Transitions of a Rigid-Rod Solution in a Thin Slit
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abstract
The equilibrium phase behavior of a confined one-dimensional rigid-rod system is analyzed computationally. The distribution functions for stable and unstable equilibrium states are computed as a function of the system density N and the system width b. The effects of the system walls are seen in several key phenomena that are systematically analyzed: (I) the existence of a thin film which undergoes a uniaxial-biaxial phase transition at a system density independent of b; (II) in the biaxial phase, a secondary aligned film which grows inward from the wall as N is increased; (III) the continuity of the biaxial-nematic phase transition in the interior of the system as a function of b; and (IV) the stability limits in N of the biaxial and capillary condensed nematic phases, as a function of b. The analysis yields surprising conclusions when compared with the phase diagram for homogeneous systems: the introduction of walls perturbs the stability limits for any system width b, contradicting the frequent assumption that walls do not impact the interior of systems with wide separation between walls. For all values of b, the growth of the secondary nematic film in the biaxial phase is more energetically favorable than increasing the density of the isotropic core. The introduction of walls also suppresses the existence of some nearly-homogeneous nematic equilibrium states. Copyright 2010 American Scientific Publishers All rights reserved.
