Toeplitz matrix formulation of polymer physics: From single chain statistics to liquid-crystalline order.

Abstract

We develop a Toeplitz matrix formulation of polymer statistics that provides a unified, analytically tractable description of flexible and semiflexible chains. Bond-vector correlations are encoded in a Toeplitz matrix, with a single parameter controlling the decay of orientational memory along the backbone. The bead-spring chain model is recovered when bond correlations vanish, whereas increasing the correlation parameter increases the Kuhn length and connects the model to the worm-like chain limit. This formulation is used to calculate the end-to-end distance, end-to-end vector distribution, and form factor of linear chains with arbitrary rigidity, capturing the crossover from random walk to local rod-like behavior. The method is extended to bottlebrush polymers by decomposing the form factor into backbone-backbone, side chain-side chain, and backbone-side chain contributions. We also analyze chain stretching and derive a nonlinear force-extension relation that exhibits a Hookean response at small deformations and captures worm-like chain behavior at intermediate stretching and freely jointed chain behavior near full extension. Finally, we derive the Green function of Toeplitz chains in external fields and use it to obtain the Lifshitz conformational entropy, which explicitly depends on the Kuhn length. Generalizing this approach to include orientational order and combining it with the two-body interaction term gives a Landau theory of the isotropic-nematic transition. The Toeplitz formulation provides a compact route for treating chain stiffness, spatial inhomogeneity, and liquid-crystalline ordering in a unified theoretical framework.