Gelation mechanisms

Fig. 4. MiceUular gelation mechanism. A shows micelle nuclei, highly cross-linked B, boundary where micelle growth terminates in styrene block polymers.

The HM and LM pectins give two very different types of gels the mechanisms of stabilization of the junction zones in the two cases are described and few characteristics given. The different molecular characteristics (DE, distribution of methoxyl or acetyl substituents, neutral sugar content or rhamnose content) play an important role on the kinetic of gelation, mechanical properties of the gel formed and also on the experimental conditions to form the stronger gels. All these points were briefly discussed. 

Amylose is an instructive example, showing the relationships between different conformations and chemical properties (28). In the discussion of gelation mechanisms, the evaluation of the fine structure of the polysaccharides is a very important point. 

C. Carrageenan and gellan gum gelation mechanism and supermolecular structure... 

The gelation mechanism of redox-Cr(III) follows the same pathway as Cr(III) salt gelation. 

The gelation mechanism is shown in Fig. 3. The spontaneous gelation was visually confirmed when the polymer concentration was 5 wt% PMBV solution and 2.5 wt% PVA solution. 

Fig. 3 Above Spontaneous gelation mechanism between the phenylboronic acid moiety (boronate ion) in water-soluble PMBV and the hydroxyl groups (diol units) in PVA. Below Photoimages of spontaneously forming PMBV/PVA hydrogel, before gelation (left), after gelation...

Fig. 4. Micellular gelation mechanism. A shows micelle nuclei, highly cross-linked B, boundary where micelle growth terminates in styrene block polymers. Styryl free radicals simultaneously initiate micelle nuclei at points of high fumarate concentration. The micelles continue to expand, interacting with free styrene until the fumarate groups are depleted. The micelles eventually overlap at the boundaries that contain higher levels of terminal styrene...

When a protein dispersion is heated a gel may form. The gelation mechanism, the gel structure and the gel properties are highly dependant on processing conditions as well as factors such as pH and ionic strength. Differences in gel structures are demonstrated in Finures 1 and 2. where electromicrographs of two gel structures of exactly the same protein preparation, formed at different ionic strengths are shown. 

With knowledge of the gelation mechanisms it may thus be possible to understand differences in gel structures. 

Many other problems remain to be solved before we can fully understand structure forming processes. Apart from knowledge of the gelation mechanisms, where the kinetics involved require further studies, more work has to be done on the molecular level as well as on the macroscopic level. The kind and nature of the crosslinks have to be investigated on the molecular level. 

---