Existence Of Liquid-liquid Critical Point Research Articles

Equation of State of Liquid Water Written by Simple Experimental Polynomials and the Liquid–Liquid Critical Point

Experimental and theoretical evidence has been accumulating to support the liquid-liquid critical point (LLCP) hypothesis for water. However, no agreement has yet been reached on the pressure and temperature of LLCP. Here we made simple experimental equations that reproduced the volume of liquid water measured over a wide pressure-temperature range. They were polynomials that calculate pressure using volume and temperature as variables, and coefficients were determined by the method of least-squares. We analyzed the polynomials by changing the volume data and the number of terms in the polynomials and extrapolated them slightly to low temperatures. Consequently, the available experimental volume of liquid water indicated (but did not prove) the existence of LLCP at low temperature. Representative polynomials suggested that LLCP locates around 105 ± ∼ 9 MPa, 207 ± ∼ 5 K, and 0.993 ± ∼ 0.009 cm3/g.

Ising Universality Class for the Liquid-Liquid Critical Point of a One Component Fluid: A Finite-Size Scaling Test

We present a finite-size scaling study of the liquid-liquid critical point in the Jagla model, a prototype model for liquids that present the same thermodynamic anomalies which characterize liquid water. Performing successive umbrella sampling grand canonical Monte Carlo simulations, we evaluate an accurate density of states for different system sizes and determine the size-dependent critical parameters. Extrapolation to infinite size provides estimates of the bulk critical values for this model. The finite-size study allows us to establish that critical fluctuations are consistent with the Ising universality class and to provide definitive evidence for the existence of a liquid-liquid critical point in the Jagla potential. This finding supports the possibility of the existence of a genuine liquid-liquid critical point in anomalous one-component liquids like water.