Structure of liquid and glassy methanol confined in cylindrical pores

We present a neutron scattering analysis of the density and the static structure factor of confined methanol at various temperatures. Confinement is performed in the cylindrical pores of MCM-41 silicates with pore diameters D=24 angstrom and D=35 angstrom. A change of the thermal expansivity of confined methanol at low temperature is the signature of a glass transition, which occurs at higher temperature for the smallest pore. This is an evidence of a surface induced slowing down of the dynamics of the fluid. The structure factor presents a systematic evolution with the pore diameter, which has been analyzed in terms of excluded volume effects and fluid-matrix cross-correlation. Conversely to the case of Van der Waals fluids, it shows that stronger fluid-matrix correlations must be invoked most probably in relation with the H-bonding character of both methanol and silicate surface.Comment: version March 12 200

A systematic study of the isothermal crystallization of the mono-alcohol n-butanol monitored by dielectric spectroscopy

Isothermal crystallization of the mono-hydroxyl alcohol n-butanol was studied with dielectric spectroscopy in real time. The crystallization was carried out using two different sample cells at 15 temperatures between 120 K and 134 K. For all temperatures, a shift in relaxation times to shorter times was observed during the crystallization process, which is characterized by a drop in relaxation strength. The two different sample environments induced quite different crystallization behaviors, consistent and reproducible over all studied temperatures. An explanation for the difference was proposed on the background of an Avrami and a Maxwell-Wagner analysis. Both types analysis suggest that the morphology of the crystal growth changes at a point during the crystallization. The differences between the cells can be explained by this transition taking place at different times for the two cells

On the correlation between fragility and stretching in glassforming liquids

We study the pressure and temperature dependences of the dielectric relaxation of two molecular glassforming liquids, dibutyl phtalate and m-toluidine. We focus on two characteristics of the slowing down of relaxation, the fragility associated with the temperature dependence and the stretching characterizing the relaxation function. We combine our data with data from the literature to revisit the proposed correlation between these two quantities. We do this in light of constraints that we suggest to put on the search for empirical correlations among properties of glassformers. In particular, argue that a meaningful correlation is to be looked for between stretching and isochoric fragility, as both seem to be constant under isochronic conditions and thereby reflect the intrinsic effect of temperature

Influence of pressure on the boson peak:Stronger than elastic medium transformation

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