“Exclusion Zone” Formation in Mixtures of Ethanol and Water

Paper published Mar 7th, 2017

link to journal; full text (PDF)

Brownian particles suspended in water or other polar liquids are pushed out of the region next to hydrophilic polymers, leaving a microsphere-free region known as the “exclusion zone” (EZ). This study aimed to test the hypothesis that the dilution of ethanol in water may influence EZ formation.

EZs were created in aqueous media using Nafion tubes as EZ-nucleating surfaces. To define the outer edge of the EZ, carboxylate microspheres, 1 µm diameter, were used. Dynamic movement of microspheres away from Nafion surface was registered in mixtures of ethanol and water, the ethanol concentration varying from 0 to 95%. We found that mixtures with the highest concentrations of ethanol generally produced the smallest EZs and the slowest EZ buildup. However, an unexpected result was the presence of an extremum corresponding to ~10% ethanol. At this concentration, the EZ is larger than in either pure water or almost pure ethanol.