Rheology of Physical Gels

However, as remarked earlier, for many gelling systems, particularly those with relatively large precursor molecules, the exponent n can be much less than the theoretical value n = 2/3. Winter and Mours (1996) provide a thorough sunmiary of these and other rheological studies of chemical gels. 

We now turn our attention from chemical to physical gels. As mentioned in the Introduction to this chapter, the junctions in physical gels can consist of locally helical structures, microcrystallites, or nodular domains. 

---

Watase M, Itagaki H (1998) Thermal and rheological properties of physical gels formed from benzylidene-D-sorbitol derivatives. Bull Chem Soc Jpn 71(6) 1457-1466 Yamasaki S, Tsutsumi H (1994) Microscopic studies of 1,3 2,4-di-O-benzylidene-D-sorbitol in ethylene glycol. Bull Chem Soc Jpn 67 906-911... 

There are three situations that appear to be relevant here. First, we may think of a solid polymer formed from the melt second, the much more compliant elastomers that initially come to mind when we think of rubber elasticity and third, polymer gels formed in polymer solutions. In each case the details of the physical chemistry of the macromolecules is crucial to the understanding of the structure that is formed. In this section we will concentrate on organic macromolecules because the rheology of these molecular systems is often the reason for their use. 

Gg (instantaneous modulus), Hg (residual viscosity) and G (shear modulus) all showed a rapid increase above 30g dm bentonite. This was attributed to the formation of a gel network structure in the continuous medium and the strength of such a gel increased with increase in bentonite concentration. The results could be qualitatively described in terms of the elastic floe model of Hunter and co-workers. Moreover, the settling characteristics of the structured suspensions were found to be consistent with the predictions from the rheological measurements. This demonstrates the value of rheological studies in predicting the longterm physical stability of suspension concentrates. 

Like the transitional physical properties, the rheological properties of gels are not easily characterized because they depend strongly on the attributes of the polymer, history of the gel sample, and experimental conditions. Most often, the apparent viscosity or gel... 

---