arXiv subjects

C. Austen Angell

Publications and source records attributed to C. Austen Angell.

21 records · Page 2Linked to original sources

arXiv2004

The Glass Transition Temperature of Water: A Simulation Study

We report a computer simulation study of the glass transition for water. To mimic the difference between standard and hyperquenched glass, we generate glassy configurations with different cooling rates and calculate the $T$ dependence of the specific heat on heating. The absence of crystallization phenomena allows us, for properly annealed samples, to detect in the specific heat the simultaneous presence of a weak pre-peak (``shadow transition''), and an intense glass transition peak at higher temperature. We discuss the implications for the currently debated value of the glass transition temperature of water. We also compare our simulation results with the Tool-Narayanaswamy-Moynihan phenomenological model.

cond-mat.soft↗

arXiv2002

Electrospray techniques for the study of liquid energetics by hyperquenched glass calorimetry

We describe an electrospray technique for in situ preparation, for differential scanning calorimetry study, of samples of molecular liquids quenched into the glassy state on extremely short time scales (hyperquenched). We study the case of propylene glycol PG in some detail. Using a fictive temperature method of obtaining the temperature dependence of enthalpy relaxation, we show that the electrospray method yields quenching rates of ~105 K/s, while the more common method, dropping a sealed pan of sample into liquid nitrogen, yields only 120 K/s. Hyperquenched samples start to relax exothermically far below the glass temperature, at a temperature where the thermal energy permits escape from the shallow traps in which the system becomes localized during hyperquenching. This permits estimation of the trap depths, which are then compared with the activation energy estimated from the fictive temperature of the glass and the relaxation time at the fictive temperature. The trap depth in molar energy units is compared with the "height of the landscape" for PG, the quasi-lattice energy of the liquid based on the enthalpy of vaporization, and the single molecule activation energy for diffusion in hydrogen bonded crystals. The implications for the topography of the energy landscape and the mechanism of its exploration, are considered.

physics.chem-ph↗

arXiv1999

Entropy and dynamic properties of water below the homogeneous nucleation temperature

Controversy exists regarding the possible existence of a transition between the liquid and glassy states of water. Here we use experimental measurements of the entropy, specific heat, and enthalpy of both liquid and glassy water to construct thermodynamically-plausible forms of the entropy in the difficult-to-probe region between 150 K and 236 K. We assume there is no discontinuity in the entropy of the liquid in this temperature range, and use the Adam-Gibbs theory -- which relates configurational entropy to dynamic behavior -- to predict that dynamic quantities such as the diffusion constant and the viscosity pass through an inflection where the liquid behavior changes from that of an extremely ``fragile'' liquid to that of a ``strong'' liquid.

cond-mat↗