X-RAY EVANESCENT WAVE-INDUCED FLUORESCENCE STUDY OF ADSORPTION OF A SULFONATED POLYSTYRENE IONOMER FROM DIMETHYL-SULFOXIDE TO THE SOLUTION VAPOR INTERFACE/

We have studied the adsorption of an ionomer, poly(styrene-ran-mangane se styrene sulfonate), from dimethyl sulfoxide solution to the solutio n/vapor interface at 20 degrees C. The polymer sulfonation level was 1 5 mol% and the solution concentration studied was 1.00% (wt/wt). The a dsorption was followed over time (4 days) by X-ray evanescent wave-ind uced fluorescence (XEWIF), which is a non-destructive probe of the pol ymer adsorption profile. We found that a state of apparent equilibrium was reached after a 4-day period and that the amount of polymer adsor bed was rather larger than anticipated from surface tension measuremen ts. This anomaly is explained by the influence of image charge forces, which increase the surface energy and must be balanced with the surfa ce energy reduction of placing the non-polar repeat segments at the su rface. We suggest that this effect may be generalized to aqueous polye lectrolytes.