Deuterium isotope effects in binary critical mixtures

Publisher Website
Google Scholar
Abstract
The shape of the liquid–liquid coexistence curve of five binary liquid mixtures containing methanol (methanol, methanol‐d1, methanol‐d4) and cyclohexane (cyclohexane, cyclohexane‐d12) is studied using a differential refractometer. It is found that all systems have approximately the same critical composition (mole fraction) and approximately the same shape of the coexistence curve in the vicinity of the critical point. However, the critical temperature changes in a characteristic manner. Replacement of hydrogen atoms involved in hydrogen bonding by deuterium leads to an increase of the critical temperature of about 1.2 K for each replaced hydrogen atom. Replacement of hydrogen atoms not involved in hydrogen bonding leads to a decrease of the critical temperature of about 0.3 K for each replaced hydrogen atom. These are average values referring to the systems methanol/cyclohexane, phenol‐d6/D2O, deutero‐isobutyric acid (COOH)/H2O, and deutero‐isobutyric acid (COOD)/D2O. Substitution of H2O by D2O in the four component system benzene, ethanol, water, ammonium sulfate of near tricritical composition increases a characteristic temperature by about 1 K.