Rheological investigation of the structural properties and aging effects in the agarose/co-solute mixture

Abstract

Small deformation dynamic oscillation, large deformation compression and creep testing were carried out to examine the structural properties of agarose in the presence of 50:50 preparations of sucrose and glucose syrup. The content of co-solute varied from 10 to 93% in the mixture. Increasing additions of sugar transform gradually the enthalpic, brittle networks of the polysaccharide to ‘rubbery’ structures of enhanced thermal stability. At saturated levels of solids there is a phase inversion from the gel-like characteristics of the agarose network to the liquid-like response of the continuous phase of co-solute. The latter undergoes vitrification upon cooling thus exhibiting the mechanical glass transition region and the glassy state. Given time, vestigial development and eventual three-dimensional linkage of agarose helices reverts the high viscosity liquids to rubbery gels exhibiting considerable yield strain (140% deformation). The work is compared to sugar/polysaccharide mixtures in the literature with the view to rationalizing underlying molecular processes and defining universal effects.