Measuring the Coexistence Curve of 8-Arm Star Polystyrene in Methylcyclohexane

Ryan Douglas Hartschuh

A new experimental setup was designed and developed to measure the refractive index of an 8-arm star polystyrene-methylcyclohexane solution in the one and two-phase regime. This particular system of branched polymer in a weak solvent has not yet been thoroughly studied as it pertains to critical phenomena and universality class. For the first time, photodiode linear arrays (position sensitive detectors) were used to detect refracted light position. A three-state copper thermostat was used to control the temperature of the sample, which was contained in a glass cell of path length 20 mm at 35° incident to the incoming beam. Substantial effort was focused towards designing, developing, testing, and calibrating the setup. When applied to the critical system of concern, preliminary data were collected, analyzed, and used to plot the coexistence curve, in refractive index and volume fraction, of the one-phase and the upper phase, but the accuracy of the data was questionable. Much was learned in terms of using the new experimental setup and quantifying error, but suggestions for improvement are discussed that may lead to an effective means of measuring the coexistence curve of 8-arm star polystyrene in methylcyclohexane.