Anisotropy in the dimensional and elastic parameters of confined macromolecules

Using lattice simulations the effect of confinement on the size, orientatio n and elastic properties of athermal chains was investigated. For chains co nfined in a slit or in a "cylinder" with square profile a minimum was obser ved in the dependence of the mean-square end-to-end distance [R-2] on the p late distance D. However, the components of the mean chain dimensions perpe ndicular and parallel to the walls, [R-perpendicular to(2)] and (Rf), stead ily diverge with reduction of the pore size. In a slit the distribution fun ctions of the chain vector perpendicular and parallel to the plates, [(R-pe rpendicular to(2)] and W[R-parallel to(2)], respectively, were computed. Th e 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 Delta A(cf) stems from this mechanism of pore-induced macromolecular orientation . A striking anisotropy was observed in the elastic free energies A(perpend icular to)(el) and A(parallel to)(el) of chains deformed in the direction p erpendicular and parallel to the walls and in the corresponding force-displ acement functions. Finally, the relation between the elastic free energy A( el) and the free energy of confinement Delta A(cf) and between the forces f and f(solv) derived thereof is analysed.