• Wientjes, R. H. W.
• Mellema, J.
• Duits, Michael
• Bakker, Jimmy
• Jongschaap, R. J. J.

Abstract

To gain more insight into the mechanisms of stress relaxation in aqueous guar gum solutions, we investigated the effect of chemical modifications of the polymer and of the solvent on the linear viscoelastic behavior in different regions of the frequency domain. Interchain bonding could be ruled out as the origin for the high-frequency relaxation behavior, while it was corroborated that such a bonding must be (directly or indirectly) involved in the relaxations at low frequencies. In the enzymatic modifications, galactose side groups were removed in different fractions f (0.30−0.57) of the available amount. Moduli were measured as a function of frequency (0.003−20 Hz) and temperature (283−323 K). On increasing f, a transition from a liquid to a gel was found at f = fc. Below fc the changes in the relaxation behavior were very modest, and changing the solvent had little effect. Above fc gels were formed. The low-frequency storage moduli strongly increased whereas the high-frequency moduli remained essentially unchanged. For both modified and unmodified guar solutions, we attribute the viscoelastic response at high frequencies to conformational relaxations of multichain structures and at low frequencies to interchain bonding effects. More detailed mechanistic information is hard to obtain. Yet we propose a microscopic picture that can explain most of our observations. It would merit a further study with other techniques. The possibility to make weak gels of α-d-galactosidase-treated guar was demonstrated, and also this deserves further study.

Topics

• impedance spectroscopy
• polymer