Simulation of nanostructure formation in rigid-chain polyelectrolyte solutions

Abstract

In the present thesis, different types of self-assembled polyelectrolyte systems have been addressed. The investigations of conformational behavior of strongly-charged PEs have been performed. To identify and characterize resulting PECs, the effect of oligocation chain length, Nc and electrostatic interactions was studied. To this end, simulations of equimolar systems containing rigid-chain polyanion and flexible-chain polycations of various lengths were performed. To identify the types of emerging conformations, various energetic and structural criteria were employed. The numerical simulation of a system of strongly charged polyanions and diblock copolymers composed of a positively charged block and a neutral block has shown that stable ionic micelles in the form of extended cylindrical brushes are formed owing to electrostatic interaction. A decrease in temperature or an increase in the charge density on the polyanion chain lead to its effective stiffening. The orientational ordering of anisotropic ionic micelles, which do not aggregate in solution, takes place at a sufficiently high concentration. The computer simulation of the systems composed of strongly charged polyanion chains and multivalent ions showed that, at certain temperatures and electrostatic interaction forces, attraction between polymer chains takes place, which results in the formation of branched structures and networks. Under these conditions, the systems are characterized by maximal values for the mean-square radius of gyration of chains and the order parameter of their arrangement. The stability ranges of network structures shift toward higher temperatures with an increase in charge of counterions. The formed porous structures were described in terms of differential void-size distribution functions.