Temperature dependence of gel properties of two-component physical gels

✍ Scribed by Ching-Feng Mao

• Publisher: John Wiley and Sons
• Year: 2006
• Tongue: English
• Weight: 405 KB
• Volume: 102
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/app.24767

✦ Synopsis

Abstract

The cascade model for mixed gels developed by the author in a previous work is extended to describe the temperature‐dependent gel properties. The equilibrium constant of the association between component polymers is assumed to depend on temperature via a van't Hoff‐type equation. The temperature variation of the network structure and gel modulus is presented and discussed at different parameters such as enthalpy change per crosslink Δ__H__°, entropy change per crosslink Δ__S__°, functionality ratio s, and concentration ratio r. It is demonstrated that the model agrees reasonably well with the experimental data obtained from the rheological gelling for galactomannan/xanthan and glucomannan/xanthan mixed gels. However, the resulting model parameters are not consistent with those obtained from the concentration dependence study. A further investigation on the calorimetric thermogram of the glucomannan/xanthan mixed gel reveals that the gelling process involves an association reaction followed by a structural rearrangement, which is beyond the scope of this work. Finally, the cascade model is shown to be consistent with the Eldridge–Ferry equation. It is also demonstrated that the sol–gel behavior of the galactomannan/xanthan mixed gel follows the Eldridge–Ferry relationship, but the calculated melting enthalpy is composition‐dependent, contrary to the assumption made in the cascade model. This discrepancy is due to the self‐association of xanthan when xanthan is present in excess amounts. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 663–673, 2006