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Light scattering study of condensation of poly(N-isopropylacrylamide) chain

The spectrum of light scattered from poly (N-isopropylacrylamide) (NIPA) chains (molecular weight M W ∼1.3×10 6 ) in water has been investigated as a function of temperature by using photon correlation spectroscopy. In a dilute solution (27 µg/cm 3 ) we observed a sharp change in polymer size that corresponds to a coil-globule transition of a single polymer chain. The transition occurred at 34.1°C, accompanied by a sharp decrease in hydrodynamic radius from 1000 to 600 A as the temperature was increased. In a semi-dilute solution (2.7 mg/cm 3 ) a phenomenon of critical slowing down in the polymer concentration fluctuations was observed around the phase separation temperature, which is very similar to the previous observation on NIPA/water gel.