Frequency-dependent specific heat near the glass transition measured with the photoacoustic effect

Dual beam differential photopyroelectric setup for broadband thermal effusivity investigation of glass transitions in polymers

The behaviour of the thermal effusivity squared over the glass transition in polystyrene is measured over a considerable frequency range using a novel dual beam front detection photopyroelectric configuration, which ensures a very effective processing of the obtained signal. This has enabled the detection of the very small changes taking place in such a parameter, despite the non-favourable sensitivity conditions due to the large mismatch between the thermal effusivities of the pyroelectric transducer and of the sample. The effect of the thermal contact resistance between the sample and the pyroelectric detector is also considered and discussed.

Thermal and optical study of the kinetics of the nematic-isotropic transition in octylcyanobiphenyl

It is shown in this paper that the kinetics of the nematic-isotropic (NI) transition in 30-microm-thick octylcyanobiphenyl liquid crystal films is strongly affected by the cell walls. We have found that this is due to the modification of the wetting properties of the liquid crystal depending on the surface treatment. The results have been obtained with an experimental setup which allows the simultaneous high resolution study of the sample thermal properties and texture evolution with temperature. An accurate determination of the width of the two phase coexistence region associated with the NI transition has been possible and it is shown that it is affected by the presence of a surfactant. The results have been interpreted with a simple model which is based on the possible presence of a well-defined interface between the nematic and the isotropic phases in the coexistence region, which depends not only on the thermal gradients in the sample but also on the surface treatments.

Solvent damping of internal processes in myoglobin studied by specific heat spectroscopy and flash photolysis

We address the question of dynamic coupling between protein and solvent by comparing the enthalpy relaxation of the solvent (75% v/v glycerol-water) to internal ligand binding in myoglobin. When the solvent relaxation is slow compared to intramolecular events we observe decoupling of protein motions from the solvent. In the opposite limit there is a significant contribution of the solvent to internal friction. The solvent enhances the apparent activation energy of transitions in myoglobin. This result is discussed in terms of a generalized Kramer's law involving a dynamic friction coefficient.