Calorimetric and compressibility study of aqueous solutions of dextran with special reference to hydration and structural change of water

Abstract

Interactions between water and dextran have been investigated by measuring specific heat capacity, adiabatic compressibility, and viscosity, with dextran samples of molecular weight above 104. For these measurements, a laboratory-constructed isoperibol twin calorimeter and an ultrasonic interferometer were used. The compressibility data show the existence of the water hydrated to dextran molecules, and the amount of hydration water was determined. The partial molar heat capacity was calculated for the structural unit of the dextran molecule. In the plot of log [η] against log Mw, a downward deviation from the linear relation was observed, and this was interpreted as due to branching of the dextran molecule. The amount of hydration water and the partial molar heat capacity decreased with the increasing molecular weight of dextran. The quantity ΔCP2∘=CP2ࢪ-CP2 (pure state) indicates that the structural change of water caused by the dissolution of one structural unit of the dextran molecule is smaller than in the case of glucose and that the degree of the structural change of water decreases sharply with the increasing molecular weight of polymers. These results are interpreted in terms of the combination of branching and increased entanglement of the polymer chain. © 1981 The Society of Polymer Science, Japan.