A thermodynamic model of physical gels

作者：An Yonghao; Solis Francisco J; Jiang Hanqing^*

来源：Journal of the Mechanics and Physics of Solids, 2010, 58(12): 2083-2099.

DOI：10.1016/j.jmps.2010.09.002

• Physical gels
• Free energy
• Thermodynamics
• Reformation
• Phase transition

Physical gels are characterized by dynamic cross-links that are constantly created and broken, changing its state between solid and liquid under influence of environmental factos. This restructuring ability of physical gels makes them an important class of materials with many applications, such as in drug delivery. In this article, we present a thermodynamic model for physical gels that considers both the elastic properties of the network and the transient nature of the cross-links. The cross-links' reformation is captured through a connectivity tensor M at the microscopic level. The macroscopic quantities, such as the volume fraction of the monomer phi, number of monomers per cross-links s, and the number of cross-links per volume q, are defined by statistic averaging. A mean-field energy functional for the gel is constructed based on these variables. The equilibrium equations and the stress are obtained at the current state. We study the static thermodynamic properties of physical gels predicted by the model. We discuss the probvlems of un-constrained swelling and stress driven phase transitions of physical gels and describe the conditions under which these phenomena arise as functions of the bond activation energy E(a), polymer/solvent interaction parameter chi, and external stress p.

• 出版日期2010-12