SPIN-HAMILTONIAN ANALYSES OF GRAFTED ROD PHASE-TRANSITIONS

We highlight here the symmetry breaking which occurs as rodlike particles are adsorbed onto a planar surface. A spin-1 Ising-variable Hamiltonian is defined which includes both bilinear and biquadratic interaction terms. Nearest-neighbor couplings are also introduced which distinguish between parallel pairs of particles having different orientations with respect to the surface normal; finally, a single-particle term describes the anisotropy in adsorption energy. By solving for the thermodynamics of this Hamiltonian in both mean-field and renormalization-group approximation, we establish the necessary conditions for the appearance of two successive fluid-fluid phase transitions.