This brief review of polymer-surfactant interaction opens by describing how polymers behave in solution. Then we survey the literature on the interaction of nonionic polymers with surfactants, and the interaction of polyelectrolytes with ionic surfactants of opposite charge. After a brief discussion of polymer adsorption at interfaces, we consider the implications of these interactions on the design of shampoo products.
Polymers in Dilute and Semi-dilute Solution
Polymer-surfactant interaction in personal care compositions usually occurs in aqueous media. In order to understand the concepts of this type of polymer-surfactant interaction, it is first necessary to grasp how typical polymers behave in solution. The condition for a polymer molecule to dissolve is that the polymer-solvent interaction is greater than both polymer-polymer and solvent-solvent interactions. If this condition is achieved the polymer will dissolve and, depending upon the concentration, a dilute solution or semi-dilute solution will be formed.
A dissolved polymer can occupy many times the volume of the polymer molecule itself—that is, a polymer swells when it is dissolved and the volume inside the swollen polymer contains solvent. It is not unusual for a dissolved polymer to be swollen to a thousand times its original size. In a dilute solution each dissolved polymer molecule will be isolated. If the polymer concentration is increased, eventually there comes a point when the entire space is filled with swollen polymer molecules and above this concentration the polymer can only occupy the solution if the molecules entangle and thread through each other’s domains.