Effects of Temperature on the Thermodynamic and Dynamical Properties of Glycerol–Water Mixtures: A Computer Simulation Study of Three Different Force Fields

Abstract

Glycerol-water solutions are relevant in technological and scientific applications, such as in the preservation of biomolecules and tissues at low temperatures. We perform molecular dynamics simulations of glycerol-water mixtures with glycerol molar fractions of χg = 0-100% at P = 0.1 MPa and T = 210-460 K. We focus on the effects of temperature and concentration on the thermodynamic (density ρ, thermal expansion coefficient αP, isobaric specific heat cP, compressibility κT) and dynamical (glycerol and water diffusion coefficients, Dg and Dw) properties of the mixtures. In particular, we test the sensitivity of computer simulation results to the glycerol force field and water model (TIP3P and TIP4P/2005) employed. All mixture models underestimate ρ at high T and tend to overestimate ρ at low T; only the mixture model based on TIP4P/2005 water exhibits a density maximum at low χg, as expected. All models overestimate αP, cP, and κT; they are able to reproduce qualitatively the T dependence of αP and κT but fail in the case of cP. In all cases, Dg and Dw follow the Vogel-Tamman-Fulcher equation and decouple at low T, with Dw/Dg increasing upon cooling. Overall, the mixture based on TIP4P/2005 water provides better thermodynamic and dynamical properties than the mixtures based on TIP3P water, even at χg = 20%.

Glass polymorphism in glycerol–water mixtures: I. A computer simulation study

“…Simulations are performed using the TIP4P/2005 model for water 54 combined with two different models for glycerol, the Blieck–Chelli 55 , 56 (BC) model that belongs to the AMBER 57 force field and the Reiling 58 (R) model that belongs to the CHARMM22 59 , 60 force field. The two mixture models, BC+TIP4P/2005 and R+TIP4P/2005, were studied in the liquid state in ref. 61 using MD simulations.…”

“…61 using MD simulations. Details of the MD simulations (such as the cutoff distance used for pair interactions), force fields (including the parameters that define each model), as well as the comparison of the models' performance with experiments can be found in ref. 61 and 62 .…”

“…In order to characterize the liquid-to-glass transformation of the water–glycerol mixtures, we also perform equilibrium simulations of the solutions at different temperatures ( T = 200–300 K) and at P = 0.1 MPa. Following ref. 61 , the starting configurations are prepared by locating glycerol molecules randomly in a water box, followed by equilibration at P = 0.1 MPa and T = 400–460 K. The temperature of the system is then lowered in steps, T = 300, 280, 240, 220, 210 K, and at each temperature the system is simulated for a time Δ t , before the temperature is further reduced.…”

Glass polymorphism and liquid–liquid phase transition in aqueous solutions: experiments and computer simulations

“…Interestingly, the results from the MD simulations were robust, not sensitive to the glycerol model used, even when the specific conformations adopted by the different glycerol models in the glass state differ. 253,259 One of the main contributions of MD simulations is to provide a molecular-level description of the LDA -HDA transformation in the glass states, information that is not easily accessible in experiments. The structural changes accompanying the LDA -HDA transformation in pure water are well-known (see, e.g., ref.…”

“…263 show that the TMD line shifts towards lower temperatures with increasing glycerol concentrations. 259 This suggests that adding glycerol to water tends to shift the LLCP to lower temperatures. Such findings are also supported by experiments since the densities obtained from these MD simulations in the liquid state are in remarkable agreement with experimental data for approximately x r 0.20.…”