An athermal solution of semiflexible macromolecules with excluded volume interactions has been studied at various concentrations (dilute, semidilute, and concentrated solutions) in a film of thickness D between two hard walls by grand canonical Monte Carlo simulations of 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 an entropic attraction and undergo a transition to two-dimensional nematic order. Due to the properties of the lattice model, this order has Ising character, and the simulation results seem to be compatible with a second-order transition. 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 isotropic-nematic 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.

Athermal solutions (from dilute to concentrated) of semiflexible macromolecules confined in a film of thickness D between two hard walls are studied by means of grand-canonical lattice Monte Carlo simulation using the bond fluctuation model. This system exhibits two phase transitions as a function of the thickness of the film and polymer volume fraction. One of them is the bulk isotropic-nematic first-order transition, which ends in a critical point on decreasing the film thickness. The chemical potential at this transition decreases with decreasing film thickness ("capillary nematization"). The other transition is a continuous (or very weakly first-order) transition in the layers adjacent to the hard planar walls from the disordered phase, where the bond vectors of the macromolecules show local ordering (i.e., "preferential orientation" along the x or y axes of the simple cubic lattice, but no long-range orientational order occurs), to a quasi-two-dimensional nematic phase (with the director at each wall being oriented along either the x or y axis), while the bulk of the film is still disordered. When the chemical potential or monomer density increase, respectively, the thickness of these surface-induced nematic layers grows, causing the disappearance of the disordered region in the center of the film.

Athermal solutions 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 have been studied by means of grand canonical Monte Carlo simulation using the bond fluctuation lattice model. In earlier work, we have reported on the phase diagram of this model system, which exhibits a continuous quasi-two-dimensional order–disorder transition at rather small concentration and (for thick enough films) a “capillary nematization”-type first-order phase transition. In the “semi-infinite” case (i.e., macroscopically thick films) the onset of nematic order is triggered by the walls (surface-induced ordering). While the focus of this previous work was on the order parameters of these phase transitions and associated surface effects, in the present paper we focus on the interplay between the conformational statistics of the semiflexible chains and these orientational ordering phenomena. In particular, we study how characteristic lengths of the chains (persistence length, end-to-end distance) depend on the local and global orientational order in the system. We show that there is a strong coupling between single-chain properties and long-range orientational order. The relation between mean-square end-to-end distance of short semiflexible chains and their persistence length predicted by the Kratky–Porod model is found to be applicable (within 10% errors) in the dilute limit, while it fails as soon as nematic short- or long-range order is present.

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