Measuring Turbidity in a Near-Critical, Liquid–Liquid System: A Precise, Automated Experiment

A ground based ( \ g ) experiment is in progress that measures the turbidity of the density-matched, binary fluid mixture methanol-cyclohexane extremely close to its liquid-liquid critical point. By covering the range of reduced temperatures t = (T- TC)/TC from 10~8 to 10~2, the turbidity measurements should allow the Green-Fisher critical exponent q to be determined. This paper reports measurements showing +0.1 % precision of the transmitted and reference iIntensities, and ±4/iK temperature control near the critical temperature of 320 K. Preliminary turbidity data show a nonzero r/ consistent with theoretical predictions. No experiment has precisely determined a value of the critical exponent t;, yet its value is significant to theorists in critical phenomena. Relatively simple critical phenomena, as in the liquid-liquid system studied here, serve as model systems for more complex behavior near a critical point.