The viscoelastic properties of a model binary polymer blend exhibiting an upper critical solution temperature phase diagram were investigated by utilizing small amplitude oscillatory and steady shear measurements. A mixture of unentangled monodisperse polystyrene and poly(phenyl methyl siloxane), exhibiting Newtonian shear viscosity, was used, and its phase diagram was established by turbidity and dynamic light scattering measurements. In the miscible region, the concentration dependence of the viscosity was adequately described by a mixing rule accounting for the surface fractions instead of volume fractions. Near the phase separation temperature and far from the glass transition, critical concentration fluctuations dominated the linear viscoelastic response and were responsible for the observed thermorheological complexity. An appropriate quantitative account of these fluctuations resulted in the accurate rheological determination of both the binodal and spinodal temperatures, extending thus the applicability of the relevant procedure earlier applied to lower critical solution temperature blends involving higher molecular weight entangled polymers. In the phase separated regime, the normal stress of the dispersed phase undergoing spinodal decomposition followed a recent scaling proposed for molecular mixtures with large viscosity difference.
Enthalpy and entropy of water sorbed by the sapwood and heartwood of ®ve local softwoods were studied: western hemlock (Tsuga heterophylla), Douglas ®r (Pseudotsuga menziesii), western red cedar (Thuja plicata), sitka spruce (Picea sitchensis), and lodgepole pine (Pinus contorta). Enthalpy and entropy show a strong negative relation to the moisture content, the absolute desorption values always being higher than the adsorption ones, but with no clear trend between and within the species. Furthermore, it is shown that the linear plot of compensation between enthalpy and entropy correlates well for water sorption in wood; that water adsorption or desorption are irreversible, and that both are enthalpy-driven mechanisms.
Enthalpie-und Entropiekompensation bei der Wassersorption verschiedener HolzartenEnthalpie und Entropie bei der Wassersorption wurden an verschiedenen Holzarten bestimmt: (Tsuga heterophyll, Pseudotsuga menziesi, Thuja plicata, Picea sitchensis), und Pinus contorta. Enthalpie und Entropie steigen mit fallender Feuchte. Die Desorptionswerte sind immer etwas ho Èher als die Adsorptionswerte. Zwischen den Holzarten gab es keine signi®kanten Unterschiede. Die lineare Kompensation zwischen Enhalpie und Entropie korrelliert gut mit der Sorption. Absorption und Desorption sind irreversible, Enthalpie-getriebene Prozesse.
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