Gel network structure

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. 

Gelation can occur either (1) from solution as a result of some change in solution conditions or as a result of chemical reaction, or (2) from the solid state by swelling of an existing network on the addition of a solvent. The latter route to gelation will not be pursued further here. Mechanisms that could lead to the formation from solution of the gel-network structures described above are discussed in the immediately following subsections. Examples of actual polymer-solvent systems in which gelation has been attributed to such mechanisms are considered in the last section. 

These are formulated as O/W or W/O emulsions with special surfactant systems and/or thickeners to give a viscosity profile similar to that of lotions, but with orders of magnitude greater viscosities. The viscosity at low shear rates (< 0.1 s ) can reach thousands of Pa s and they retain a relatively high viscosity at high shear rates (of the order of few hundred Pa s at shear rates > 1 s ). These systems are sometimes said to have a body , mostly in the form of a gel-network structure that may be achieved by the use of surfactant mixtures to form liquid crystalline structures. In some case, thickeners (hydrocolloids) are added to enhance the gel-network structure. 

The above mixtures produce a viscoelastic structure that gives a bodying effect to the formulation through the formation of a gel network of lamellar liquid crystalline phases [53]. Sometimes, glycerol is also added and this is thought to affect the hydration of the ethoxylate chain, thus affecting the final gel network structure. White soft paraffin may also be added to enhance the gel structure. 

Carbohydrate-based nanofoams - Aerogels or nanofoams can be made by replacing the liquid solvent in a gel by air with the objective to minimize the substantial alteration of the gel network structure and volume. Nanofoams have unique physical and thermal properties such as low density, high specific surface area, low thermal conductivity, and low dielectric permittivity. The replacement of the liquid in a gel with air can be done with supercritical drying, but also ambient-pressure drying is an option (23,28-32). There are three classes of... 

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