THE EFFECT OF ANNEALING ON THE CONFORMATIONAL PROPERTIES OF XANTHAN HYDROGELS

Investigation of the nature of the freezing bound water in xanthan hyd rogels by differential scanning calorimetry (d.s.c.) reveals a depende nce of the area, temperature and number of the freezing exotherms on t he period of time that the gel was maintained at a temperature greater than the gel-sol transition temperature (T). Small-angle X-ray scatt ering (SAXS) and synchrotron orbital radiation (SOR) experiments show a correlation between the holding time of the gel at temperatures in e xcess of T and the size of the junction zones which maintain the inte grity of the gel. High-temperature annealing also increases the elasti c moduli of the gels. These results are discussed in terms of a genera l model for the dynamic structure of polysaccharide junction zones pre viously proposed by the authors.