RHEOLOGY OF GALACTOMANNAN-BORAX GELS

The rheological behavior of semidilute galactomannan solutions in the presence of borax has been studied. The effects of polymer and borate concentrations, ionic strength, pH, and temperature are investigated and discussed. The shape of the viscoelastic functions of galactomannan–borax gels is similar to that for semidilute or concentrated polymer solutions. In 1 M NaCl, electrostatic effects are screened and the characteristic moduli of the gels appear to be determined by the number of interchain crosslinks. The elastic plateau modulus varies linearly with the free borate concentration and with the 2.6 power of the galactomannan concentration. Time–temperature type superposition is applicable if a vertical shift is introduced to account for the exothermic nature of the complexation reactions. Moreover, it seems possible to control the gel reversibility and the lifetime of crosslinks by changing the complexation kinetics via the pH. Copyright © 1990 John Wiley & Sons, Inc.