| An athermal solution of semiflexible macromolecules with excluded volume interactions and with varying concentration (dilute, semidilute and concentrated solutions) in a film of thickness D between two hard walls has been studied by means of grand canonical Monte Carlo simulations using the bond fluctuation lattice model. Analyzing profiles of orientational order parameters across the film, we find that for thick films two phase transitions occur at chemical potentials of the polymers (or polymer densities, respectively) where the bulk polymer solution still is in the disordered isotropic phase. At rather small polymer densities polymers accumulate at the walls due to a depletion attraction and undergo a transition to two-dimensional nematic order. Due to the properties of the bond fluctuation model, this order has Ising character, and the transition is either weakly of first order or second order. Increasing the polymer density, nematically ordered ”wetting” layers form at both walls; the increase of thickness of these layers is compatible with a logarithmic divergence when the chemical potential of the isotropicnematic transition in the bulk is approached. In a system of finite width, D, between the walls this leads to capillary nematization, exhibiting a reduction of the transition chemical potential inversely proportional to D. This transition exists only if D exceeds some critical value Dc, while the transition from the isotropic phase to the two-dimensional nematic state is suggested to persist down to ultrathin films. |
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