Instrumental Methods for Analyzing Polymer Solution Interfaces

6 INSTRUMENTAL METHODS FOR ANALYZING POLYMER SOLUTION INTERFACES 

A series of modem instmments have been designed to study the conformations and other aspects of polymer chains bound to a surface. 

1 The Force Balance Apparatus (Surface Forces Apparatus) 

Consider a polymer chain adsorbed on a surface, all immersed in a liquid phase. In general, the polymer chains are partly dissolved, with those portions composed of loops and tails. These may have conformations similar to that of random coils. When two such adsorbed polymer chains approach one another, there will be an entropic repulsive force between them, arising from the excluded volume effect, as well as other forces (65,66). Sometimes the repulsive forces are called steric or overlap repulsion. 

Chains attached to colloidal surfaces provide powerful forces for stabilization. Colloidal particles that normally coagulate from a solvent dispersion can thus be stabilized by adding a small amount of polymer to the dispersion. Such polymer additives are sometimes known as protective colloids, leading to steric stabilization. Both synthetic polymers and biopolymers such as proteins and gelatin are commonly used in both nonpolar and polar solvents. Industrially they are used in paints, toners, emulsions, suspensions, cosmetics, pharmaceuticals, processed foods, and lubricants. 

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