pHandtemperatureeffectsonrheologicalbehaviorofKGM in water
Fig. 1 shows the changes viscoelastic modulus of KGM solu- tion with temperature increase (20–80 ◦ C) at various pH levels. The rheological measurements showed a high reproducibility, with errors less than 3%. KGM presented significantly different rheolog- ical behaviors with the pH changes as shown by Fig. 1. At pH 4 (Fig. 1a) and pH 7.0 (Fig. 1b), the storage modulus (G′) was close to the loss modulus (G′′) at 20◦C, and as the temperature increased, G′′ became higher than G′ . This tend suggests that KGM at 20 ◦ C was in the colloidal solution-to-gel transition state and remained in a colloidal solution as the temperature exceeded 20◦C in acidic and neural conditions. Another trend was the linear decline of G′ and G′′ with temperature increase to a very low level at 80 ◦ C, implying the weakening of inter- and intra-molecular attraction forces rapidly by heating, which may involve the degradation of polymer chain and dissociation of polymer aggregates. At pH 9.0 (Fig. 1c), the ini- tial moduli at 20 ◦ C were significantly higher, and dropped sharply