The rubber-to-glass transition in high sugar agarose systems

The small and large deformation properties of agarose in the presence of hi gh levels of sugar were investigated Mixtures can be described as lightly c ross-linked rubbers, which undergo vitrification upon cooling. The combined Williams-Landel-Ferry (WLF)/free volume framework was used to derive the g lass transition temperature, the fractional free volume, and the thermal ex pansion coefficient of the glass. Sucrose-rich cosolute crystallizes, bur a ddition of rite polymer encourages intermolecular interactions, which trans form the mixture into a high viscosity glass. The mechanical properties of glucose syrup, a noncrystalline sugar follow WLF behavior in the glass tran sition region and revert to an Arrhenius-type prediction in the glassy stat e. Measurements on sugar samples and agarose-sugar mixtures were resolved i nto a basic function of temperature alone and a basic function of frequency (time) alone. The former traces the energetic cost of vitrification, which increases sharply with decreasing temperature. The latter at long rime sca les, is governed by the infinite molecular weight of the agarose network. I n the region of short times, the effect of free volume is active regardless of the sample composition. (C) 1999 John Wiley & Sons, Inc.