Drying Mechanism of Poly(N-isopropylacrylamide) Microgel Dispersions

The drying mechanism of poly(N-isopropylacrylamide) (pNIPAm) microgel dispersions was investigated. The microgels were synthesized by temperature-programmed aqueous free radical precipitation polymerization using NIPAm, N,N'-methylenebis(acrylamide), and water-soluble initiator. Drying processes of the microgel dispersions were observed with a digital camera and an optical microscope, and the resultant dried structures were observed by scanning electron microscopy. We found that the presence of the microgels changed the behavior of the drying process of water. In particular, the microgels were adsorbed at the air/water interface selectively within a few minutes irrespective of the microgel concentration. The relationship between the drying mechanism and structure of the resultant microgel thin film has been clarified by changing the microgel concentration of the dispersions.