Poly(N-isopropylacrylamide) Microgels at the Air−Water Interface

The surface tension of colloidal poly(N-isopropylacrylamide) (PNIPAM) dispersions was measured as functions of surface age, temperature, and the morphology of the PNIPAM microgels. The microgels lowered the surface tension of water to about 43 mJ/m2 at 25 °C and a little less at 40 °C. The steady-state surface tension values were not very sensitive to temperature or to the degree of microgel cross-linking. On the other hand, the time required …