The Effect of Short‐Range Hydrogen‐Bonded Interactions on the Nature of the Critical Point of Ionic Fluids. Part II: Static and Dynamic Light Scattering on Solutions of Ethylammonium Nitrate in n‐Octanol

Abstract 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 x 1 = 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.

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