The Dilute Solution-Solid Interface

Another system of great interest relates to the interactions between solid surfaces and dilute polymer solutions. Frequently the solids in question are in the form of colloids, presenting areas of the order of 50 to 300 m% to the exterior solution phase. The polymer chains may be bondable to the solid surfaces at one end, both ends, and/or along the chain, depending on the chemistry. 

A common example of such a system is ordinary latex paint, containing both polymer latexes and inorganic fillers and pigments, and dispersed in an aqueous phase. The aqueous phase usually contains a dilute solution of polymers capable of associative bonding, that is, bonding weakly with the colloidal solids and/or each other. Such associative bonding increases the viscosity significantly and, more important, contributes a thixotropic nature to the paint see Section 10.5.5. 

In simplified terms the thixotropic action is as follows The can of latex paint starts with a high viscosity. Sticking a brush in it produces a high shear rate, lowering the viscoisty and allowing the paint to flow easily onto the brush. Raising the brush out of the paint and holding it aloft is a low shear situation for the paint on the brush, and the viscosity increases. This last produces the 

Assume a solution of 200,000 g/mol polystyrene saturating a colloidal surface. Weight increases show that there is 2.5 mg of polymer for each m of surface. What is the bound fraction of polymer  

02 X10 mers/mol Assuming a cubical shape for the mer, the area of one side is 

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