The Effects of Controlling Osmotic Pressure on a Pαms Microencapsulated Mandrel During Curing

Poly(α-methylstyrene) (PαMS) mandrel precursors (a PαMS containing fluorobenzene solution surrounding a water core) are suspended in a salt-containing water solution during curing. The salt is necessary to suppress the growth of water drops in the curing oil phase (resulting in vacuoles in the dried mandrel). However the use of salts in this manner results in a chemical potential difference between the inner pure water droplets and the outer bath. This results in a loss of water from the inner water phase, shrinking the mandrel as it cures and potentially wrinkling its surface. We have quantified the degree of mandrel shrinkage and expansion as a function of the difference in salt concentration. Expansion is not proportional to concentration difference. It does not appear that osmotically driven expansion removes wrinkles; the large wrinkle amplitudes were seen with all salt concentrations.