Poly(N-isopropylacrylamide) (PNIPAM) microgels were synthesized by emulsion polymerization using sodium dodecyl sulfate (SDS). After removal of SDS by dialysis, the surface tension of the PNIPAM microgel dispersion was measured by the pendant drop method, and it was found that the surface tension of the microgel dispersion is much smaller than that of water at 25°C. Also, the stability of the foams generated by nitrogen bubbling through the PNIPAM microgel dispersion was investigated. At 25°C, the stable foam was observed, while no stable foam was formed at 60°C. Moreover, the stable foam prepared at 25°C quickly disappeared when the temperature was changed to 60°C. These results suggest that the PNIPAM microgel has a temperature-responsive surface-activity.
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