The effects of controlling osmotic pressure on a P alpha MS microencapsulated mandrel during curing

Poly(alpha-methylstyrene) (P alpha MS) mandrel precursors (a P alpha MS con taining fluorobenzene solution surrounding a water core) are suspended in a salt-containing water solution during curing. The salt is necessary to sup press the growth of water drops in the curing oil phase (resulting in vacuo les in the dried mandrel). However the use of salts in this manner results in a chemical potential difference between the inner pure water droplets an d the outer bath. This results in a loss of water from the inner water phas e, shrinking the mandrel as it cures and potentially wrinkling its surface. We have quantified the degree of mandrel shrinkage and expansion as a func tion of the difference in salt concentration. Expansion is not proportional to concentration difference. It does not appear that osmotically driven ex pansion removes wrinkles; the large wrinkle amplitudes were seen with all s alt concentrations.