UNIVERSAL SCALING PARAMETER IN THE COIL-TO-GLOBULE TRANSITION

The coil-to-globule transition of the radius of gyration of polystyrene (PS) samples (M(w): 3.84 X 10(6)-8.42 x 10(6) g/mol) in methylcyclohexane (MCH) solvent has been measured by static light scattering below the theta-temperature (theta = 69.3-degrees-C). In order to analyze our coil-to-globule data as well as already-reported data of polystyrene/cyclohexane (PS/CH) and polystyrene/methyl acetate (PS/MA) systems, (M(w)/R(o)2)3/2\tau\/tau(c) was introduced as a new scaling parameter. The master curve of each system overlapped in the plot of alpha(s)3(M(w)/R(o)2)3/2\tau\/tau(c) versus (M(w)/R(o)2)3/2\tau\/tau(c). Thus this seems to be a universal parameter in coil-to-globule transition. On the basis of this observation, we concluded that the system dependence of the asymptotic height of the globular regime in the plot of alpha(s)3\tau\M(w)1/2 versus \tau\M(w)1/2 resulted mainly from the difference of the temperature width (i.e., theta - T(c)) of the theta-regime in the phase diagram of polymer solution. Here R(o), alpha(s)[=R(g)(T)/R(g)(theta)], tau[=(T- theta)/theta], and tau(c)[=(theta - T(c))/theta] are the unperturbed end-to-end distance, the expansion factor of the radius of gyration, the reduced temperature, and the reduced critical temperature, respectively.