Environmental chamber with controlled temperature and relative humidity for ice crystallization kinetic measurements by atomic force microscopy.

The present work describes the development of an environmental chamber (EC), with temperature and humidity control, for measuring ice growth kinetics over a substrate with an atomic force microscope (AFM). The main component of the EC is an AFM fluid glass cell. The relative humidity (RH) inside the EC is set by the flow of a controlled ratio of dry and humid nitrogen gases.

Glass Transition Temperature of Saccharide Aqueous Solutions Estimated with the Free Volume/Percolation Model.

The glass transition temperature of trehalose, sucrose, glucose, and fructose aqueous solutions has been predicted as a function of the water content by using the free volume/percolation model (FVPM). This model only requires the molar volume of water in the liquid and supercooled regimes, the molar volumes of the hypothetical pure liquid sugars at temperatures below their pure glass transition temperatures, and the molar volumes of the mixtures at the glass transition temperature. The model is simplified by assuming that the excess thermal expansion coefficient is negligible for saccharide-water mixtures, and this ideal FVPM becomes identical to the Gordon-Taylor model.

Structural transitions and dipole moment of water clusters (H2O)(n=4-100).

The properties of water clusters (H(2)O)(n) over a broad range of sizes (n=4-100) were studied by microcanonical parallel tempering Monte Carlo and replica exchange molecular dynamics simulations at temperatures between 20 and 300 K, with special emphasis in the understanding of relation between the structural transitions and dipole behavior. The effect of the water interaction potential was analyzed using six nonpolarizable models, but more extensive calculations were performed using the TIP4P-ice water model. We find that, in general, the dipole moment of the cluster increases significantly as the cluster melts, suggesting that it could be used to discriminate between the solidlike and liquidlike phases.