Dynamic viscoelasticity study of the phase transition of poly(N-isopropylacrylamide)

摘要

Communication: The phase transition of poly(N-isopropylacrylamide) (poly(NIPAM)) solutions was characterized by a dynamic fluid rheometer. Two critical points were observed below the tower critical solution temperature (LCST; approximate to 31.5 degrees C): (1) a critical point resembling sol-gel transition occurs at approximate to 28.5 degrees C, not far beyond the onset of elasticity (approximate to 28.2 degrees C), and (2) a second critical point; appears at approximate to 30.4 degrees C corresponding to the reported Flory temperature (Theta). These findings suggest that intermolecular association and coil-globule transition of poly(NIPAM) occur below the LCST, The fractal dimension of association of poly(NIPAM) chains which was calculated based upon the rheological method (approximate to 1.49) is close to that determined by static light scattering. [References: 37]