The general premise of this chapter is to address thermodynamic behaviors and structure of charged macromolecules in non-dilute conditions, such as semidilute and concentrated solutions. After a summary of uncharged macromolecules in concentrated solutions, the coupling between the electrostatic and topological correlations is treated. Five regimes of polymer concentrations are outlined accompanied by a collection of experimental data. Spontaneous formation of large aggregates formed by similarly charged macromolecules is described in detail.

The scope of the book is outlined with specific examples of phenomenology that are outlined and explained in subsequent chapters. The necessity of bridging electrostatic and topological correlations to understand the behavior of charged macromolecules is addressed.

This chapter introduces important concepts such as Gouy-Chapman length, double-layer, Manning condensation, and regularization of the charge of a geometrical object in electrolyte solutions. A clear description of counterion distribution around charged objects is presented.

This brief epilogue emphasizes that this book is a gateway to new avenues in addressing living matter and new water-based materials.

This chapter summarizes the various models to treat isolated uncharged flexible chains and outlines the properties of the chains with a comparison with experimental results. The summary presented in this chapter is the first step to enter into the field of charged macromolecules.

Starting from a general description of model gels and key experimental variables, thermodynamics and swelling equilibria are described. Based on the fundamentals, behaviors of gels under tension, shear, and temperature variation are explained using a combination of theory and experiments. Phase transitions of gels, where volume changes of several orders of magnitude are of common occurrence, are presented in details to enable researchers to design new hydrogels for their intended industrial purpose.

This chapter reviews basics of electrostatics in vacuum and dielectric media, ion solvation, hydrophobic effect, and thermodynamic properties of electrolyte solutions. Debye-Huckel theory is presented with emphasis on electrostatic screening and corrections to ideal solution properties.

Using the Flory-Huggins theory for uncharged polymer solutions, key concepts of the critical point, coexistence curve, and spinodal curve are presented. These concepts are then generalized to charged systems by explicitly considering restricted primitive model for electrolytes and new developments for polyelectrolyte solutions that include the liquid-liquid phase separation invoked in the formation of membrane-less organelles. Fibrillization in amyloids and collagen is discusses with a focus of electrostatic effects.