Physics
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Item Two-State Thermodynamics of Supercooled Water(2016) Biddle, John W.; Anisimov, Mikhail A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Water has been called the “most studied and least understood” of all liquids, and upon supercooling its behavior becomes even more anomalous. One particularly fruitful hypothesis posits a liquid-liquid critical point terminating a line of liquid-liquid phase transitions that lies just beyond the reach of experiment. Underlying this hypothesis is the conjecture that there is a competition between two distinct hydrogen-bonding structures of liquid water, one associated with high density and entropy and the other with low density and entropy. The competition between these structures is hypothesized to lead at very low temperatures to a phase transition between a phase rich in the high-density structure and one rich in the low-density structure. Equations of state based on this conjecture have given an excellent account of the thermodynamic properties of supercooled water. In this thesis, I extend that line of research. I treat supercooled aqueous solutions and anomalous behavior of the thermal conductivity of supercooled water. I also address supercooled water at negative pressures, leading to a framework for a coherent understanding of the thermodynamics of water at low temperatures. I supplement analysis of experimental results with data from the TIP4P/2005 model of water, and include an extensive analysis of the thermodynamics of this model.Item Asymmetric Fluid Criticality(2011) Bertrand, Christopher Elliot; Anisimov, Mikhail A; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work investigates features of critical phenomena in fluids. The canonical description of critical phenomena, inspired by the Ising model, fails to capture all features observed in fluid systems, specifically those associated with the density or compositional asymmetry of phase coexistence. A new theory of fluid criticality, known as "complete scaling", was recently introduced. Given its success in describing experimental results, complete scaling appears to supersede the previous theory of fluid criticality that was consistent with a renormalization group (RG) analysis of an asymmetric Landau-Ginzburg-Wilson (LGW) Hamiltonian. In this work, the complete scaling approach and the equation of state resulting from the RG analysis are shown to be consistent to order ε, where ε = 4 - d with d being the spatial dimensionality. This is accomplished by developing a complete scaling equation of state, and then defining a mapping between the complete scaling mixing-parameters and the coefficients of the asymmetric LGW Hamiltonian, thereby generalizing previous work [Phys. Rev. Lett. 97, 025703 (2006)] on mean-field equations of state. The seemingly different predictions of these approaches are shown to stem from an intrinsic ambiguity in the interpretation of the ε-expansion at fixed order. To first order in ε it is found that the asymmetric correction-to-scaling exponent θ5 predicted by the RG calculations can be fully absorbed into the 2β exponent of complete scaling. Complete scaling is then extended to spatially inhomogeneous fluids in the approximation η=0, where η is the anomalous dimension. This extension enables one to obtain a fluctuation-modified asymmetric interfacial density profile, which incorporates effects from both the asymmetry of fluid phase coexistence and the associated asymmetry of the correlation length. The derived asymmetric interfacial profile is used to calculate Tolman's length, the coefficient of the first curvature correction to the surface tension. The previously predicted divergence of Tolman's length at the critical point is confirmed and the amplitude of this divergence is found to depend nonuniversally on the asymmetry of the correlation length.