Anisotropy in the dimensional and elastic parameters of confined macromolecules

Using lattice simulations the effect of confinement on the size, orientation and elastic properties of athermal chains was investigated. For chains confined in a slit or in a “cylinder” with square profile a minimum was observed in the dependence of the mean-square end-to-end distance 〈R2〉 on the plate distance D. However, the components of the mean chain dimensions perpendicular and parallel to the walls, 〈R2⟂〉 and 〈R2∥〉, steadily diverge with reduction of the pore size. In a slit the distribution functions of the chain vector perpendicular and parallel to the plates, W〈R2⟂ 〉 and W〈R2∥〉, respectively, were computed. The marked difference between these distribution functions is interpreted as a sign of enhanced alignment of chains of the shape of elongated ellipsoids along the pore walls. A major part of the free energy of confinement ΔAcf stems from this mechanism of pore-induced macromolecular orientation. A striking anisotropy was observed in the elastic free energies Ael⟂ and Ael∥ of chains deformed in the direction perpendicular and parallel to the walls and in the corresponding force-displacement functions. Finally, the relation between the elastic free energy Ael and the free energy of confinement ΔAcf and between the forces f and fsolv derived thereof is analysed.