To preserve the original morphology, the microcapsules were first immobilized in 4% glutaraldehyde for 1 h, followed by pure water wash for several times. Subsequently, the dehydration was carried out through an ethanol gradient (25%, 50%, 75%, and 100%) for 10 min each and then dried in the vacuum oven or the liquid carbon dioxide at its super critical point. The PF and PF-4 samples were dehydrated by an ethanol gradient and dried in the liquid carbon dioxide at its super critical point. The immobilized microcapsules, PF and PF-4 samples were coated with a thin film of gold and observed under SEM (JSM-7800F, 5 kV).