The Turbidity and Correlation Length Amplitude of 8-arm Star Polystyrene in Methylcyclohexane Near The Critical Point

Nithya Leela Venkataraman

Many studies have been conducted on characterizing linear polymers in a polymer-solvent system near its critical point, and few studies have only been done on star polymers. This paper focuses on 8-arm star polystyrene in the weak solvent methylcyclohexane. The purpose of this experiment is to determine the correlation length amplitude, ξ0, for different molecular weights of 8-arm star polystyrene and to determine any universal dependence of the critical exponent, n, with the molecular weight. A light scattering method was used to calculate the turbidity of the solution at different temperatures near the critical temperature, and to determine the critical temperature. Then, the values obtained for the turbidity and the critical temperature were used to determine a value for ξ0. The correlation length amplitude for 8-arm star polystyrene (Mw = 228 000) in methylcyclohexane was determined to be 1.134±0.025nm. This value for ξ0 is inconsistent with the ξ0 determined for other molecular weights earlier observed in this lab. The previous molecular weights observed will need to be reexamined, and more molecular weights will need to be observed before a value for the universality of ξ0 with the molecular weight can be determined.