Properties of thermoreversible gels

Abstract

In a short survey chemical and physical aspects characterising thermoreversibly gelling systems are gathered. Rheological properties of the system gelatin/water for different polymer concentrations at various temperatures and varying angular frequencies are presented. The results are interpreted following the percolation theory. The relevant exponents of the storage and loss modulus are close to the percolation model of Arbabi and Sahimi. The pre‐gel properties favour the Zimm‐limit whereas the post‐gel properties are close to the Rouse‐limit. This controversial behaviour is discussed. The gel‐point has been determined by the divergence criterion of the dynamic viscosity at zero frequency when the storage modulus vanishes. The critical times in the percolation results agree fairly well with the time of gelation but not with the cross over time of the storage and loss modulus curves versus time at zero frequency. An equilibrium aggregation model for the post gelation processes is presented which is based on the percolation approach. The time dependence of the storage modulus can be described in the total time range between gel point and the final equilibrium value after very long times.

A Comparison of Mechanical and Electrical Percolation during the Gelling of Nafion Solutions

“…It has been proposed that a physical cross-linking might occur . This is similar to what is observed for other associating polymers which form a physical gel at higher concentration. , Since Nafion is an ionomer, this is of particular interest as it opens the way for a comparative study of electrical and mechanical properties of a gel, which has been a subject of several theoretical papers. − In this paper we therefore compare the mechanical and electrical properties of Nafion solutions. Both Nafion in the proton and the sodium forms are studied to see whether the difference in performance observed for Nafion membranes in those two forms can be related to structural differences in solution.…”

“…6 This is similar to what is observed for other associating polymers which form a physical gel at higher concentration. 8,9 Since Nafion is an ionomer, this is of particular interest as it opens the way for a comparative study of electrical and mechanical properties of a gel, which has been a subject of several theoretical papers. [10][11][12] In this paper we therefore compare the mechanical and electrical properties of Nafion solutions.…”

Effectiveness of a Developed In-House Breast Phantom in Enhancing the Knowledge of Mammographic Positioning in Radiologic Technology Students: A Quasi-Experimental Study in Thailand

“…6 The thermoreversible gel can be inserted into the breast and chest area to reproduce a breast density close to the that of a Thai female breast 7 . With this combination of materials, the breast phantom enables authentic manual positioning and compression with the thermoreversible gel, allowing the flexibility needed for the phantom to revert to its original shape 8 .…”