Liquid-liquid binary systems and their phase equilibria are important for many industrial applications. Much research has been done to characterize these coexistence curves. Recently, anomalous phase separation behavior called pre-transition droplet formation (PTDF) has been observed near the critical regions of seven liquid-liquid systems. PTDF occurs on one side of the phase diagram: trace droplets appear to separate from the mother phase ~0.1 °C above the bulk separation phase transition. This suggests that two different phase transitions are occurring, and implies the existence of a third phase in systems that were previously considered to form at most two. In this work, efforts were made to determine the composition of PTDF droplets formed in the aniline + cyclohexane system (ACH). To determine the ACH coexistence curve by the synthetic method, pure components were transferred into 3-mL ampules using gas tight syringes. The samples were purged of dissolved gases using freeze-pump-thaw cycles and then flame-sealed. Transmitted, 2°, and 90° laser light scattering signals were collected as a function of temperature and analyzed to determine coexistence curve temperatures. The critical temperature TC was found to be 303.17 ± 0.04 K, and the critical composition was found to be XAni,C of 0.4470 ± 0.0016. Efforts were then made in order to extract and characterize the droplets using a large scale instrument with a 100 mL sample. The ACH coexistence curve was re-characterized using the analytical method and gas chromatography / mass spectrometry analysis.

Pre-transition droplet formation in liquid-liquid binary systems

254th National Meeting (2017)

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