THE EFFECT OF SHORT-RANGE HYDROGEN-BONDED INTERACTIONS ON THE NATURE OF THE CRITICAL-POINT OF IONIC FLUIDS .2. STATIC AND DYNAMIC LIGHT-SCATTERING ON SOLUTIONS OF ETHYLAMMONIUM NITRATE IN N-OCTANOL

We report on static and dynamic light scattering measurements of near-critical fluctuations of an ionic liquid. The system is ethylammonium nitrate (EAN) dissolved in n-octanol which exhibits a liquid-liquid phase transition in the salt-rich regime with an upper critical point near 315 K at a mole fraction of the salt x1 = 0.773. The correlation lengths and scattering intensities scale with temperature corresponding to an Ising-like critical point. This contrasts with previous observations of mean-field behaviour in electrolyte systems with liquid-liquid phase transitions driven by long-range Coulombic interactions. Rationalizations of this discrepancy are offered taking into account a) the competition of intermolecular interactions with long-range and short-range character and b) the possibility of crossover from mean-field to Ising behaviour as predicted by the Landau-Ginzburg theory.