Phase Transitions of Hexadecane in Poly(alkyl methacrylate) Core-Shell Microcapsules

Microcapsules containing subfemtoliter Volumes of n-hexadecane (HD) within a 4-40 nm thick shell of poly(alkyl methacrylates) were prepared. The size of the HD drop was varied between 50 and 140 nm. The alkyl substituents on the methacrylate monomer were varied to alter the surface tension between the HD and the polymer shell in order to investigate the effects of surface tension on the freezing point of the HD. The size dependence of the Supercooling as predicted by the G-T equation was not observed in our systems. An effect oil the magnitude of supercooling with variation in the side chains was observed, where freezing the HD in capsules with bulkier side chains requires a greater magnitude of supercooling. This is in agreement with the increased hydrophobic character of the polymers and also correlates with the decrease in glass transition temperature of the polymer. We also observed aging of the capsules, which could be accelerated by heating.