Role of entropy in charged polymers and its complexes

The thermodynamics of charged polymer systems is characterized by the interaction potentials and entropy of the connected monomers and free counterions respectively. We review the role of entropy in several charged polymer systems. From single polyelctrolyte(PE) chain to PE networks it is seen that the ideal gas entropy of free counterions and the configurational entropy of polymers play important roles in determining the equilibrium structure of the PEs. The pressure due to confined counterions is important in dictating the kinetics of conformational changes in single PE chain. In PE gels, the free ion entropy lurks beneath the mixing entropy to characterize its swollen state in solution. A system of two oppositely charged interacting polyelectrolytes identify the strong role played by the free counterion entropy in complex formation and shows its dependence on the ambient conditions, like temperature and salt concentration. Though the bound ion pair enthalpy is an important entity in charged polymer systems, the complexation between two oppositely charged PE chains show a large release of counterions from the respective chains, resulting in a large entropy gain which drives the process.