Characterization of the LCST behaviour of aqueous poly(N-isopropylacrylamide) solutions by thermal and cloud point techniques

A systematic investigation of the phase separation behaviour of aqueous low molecular weight PNIPA solutions was carried out in order to quantitatively investigate the effect of measurement conditions on the reported phase separation temperatures in relation to three techniques, namely, differential scanning calorimetry, optical cloud point and u.v. turbidimetry. The PNIPA concentration was varied in the range 0.5-22 wt%. All three techniques yielded comparable phase separation temperatures, independently of the transition kinetics, provided that the time scale of the experiments is large enough to ensure close to equilibrium conditions. (C) 1997 Elsevier Science Ltd.