Title: Role of Entropy in Charged Polymers - A Theoretical Perspective Authors: Arindam Kundagrami [1,2]* , Soumik Mitra [1] , Souradeep Ghosh [1]

Speaker: Dr. Arindam Kundagrami, IISER Kolkata

Abstract: The thermodynamics of a charged polymer system is characterized by the interaction potentials, conformational entropy of the polymer chains and entropy of free counterions and salt ions. We review a few theories which investigate the comparative roles of entropy to enthalpy in several charged polymer systems. From a 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 a single PE chain. In PE gels, the free ion entropy is accounted for by the mixing entropy to characterize its swollen state in solution. A system of two oppositely charged polyelectrolytes displays the critical role played by the entropy of free counterions in complex formation, and shows its strengths comparative to Coulomb energy and dependence on the ambient conditions, like temperature, dielectricity and salt concentration. Although the Coulomb energy is an important entity in charged polymer systems, the complexation between two oppositely charged PE chains shows a large release of counterions from the respective chains, resulting in a large entropy gain which drives the process. The concept can be generalized to asymmetric and partially ionized polymers, and also to intrinsically disordered proteins (IDP).

Keywords: polyelectrolytes, entropy, free energy, complexation, kinetics

References: 1. Mitra, Soumik and Kundagrami, Arindam. 2023."Polyelectrolyte Complexation of Two Oppositely Charged Symmetric Polymers: A Minimal Theory." The Journal of Chemical Physics, 158, 014904-20

2. Sen, Swati and Kundagrami, Arindam. 2017."Charge-regularized swelling kinetics of polyelectrolyte gels: Elasticity and diffusion." The Journal of Chemical Physics, 147, 174901- 11

3. Mitra, Soumik and Kundagrami, Arindam. 2017."Kinetics of Swelling and Collapse of a Single Polyelectrolyte Chain." Macromolecules, 50, 2504-2517