Reversible gels definition

In 1861. Thomas Graham first used the term syneresis to describe the phenomenon of exuding small quantities of liquid hy gels. By definition, syneresis is the spontaneous separation of an initially homogeneous colloid system into lwo phases—a coherent gel and a liquid. The liquid is actually a dilute solution whose composition depends upon the original gel. When the liquid appears, the gel contracts, but there is no net volume change. Syneresis is reversible if the colloid particles do not become ton coagulated immediately after their formation. 

A definite prediction of DLVO theory is that charge-stabilized colloids can only be kinetically, as opposed to thermodynamically, stable. The theory does not mean anything at all if we cannot identify the crystalline clay state (d 20 A) with the primary minimum and the clay gel state (d 100 to 1000 A) with the secondary minimum in a well-defined model experimental system. We were therefore amazed to discover a reversible phase transition of clear thermodynamic character in the n-butylammonium vermiculite system, both with respect to temperature T and pressure P. These results rock the foundations of colloid science to their roots and... 

The chapter has examined advantages of TLC, definitions, structure, occurrence, function, sample preparation, sorbents, mobile phases, usual modes of development, and detection procedures for lipids. Although a discussion of 2-D lipid analysis has been provided, mention was not made of the newer technique of multiphase TLC, in which components are separated in two different directions according to different parameters, e.g., conventional silica gel in one direction and reversed phase in the other direction. Ritchie and Jee (143) have used this technique for the analysis of triacylglycerols. 

---