Gelled aqueous systems

A Silberberg. Gelled aqueous systems. In J Glass, ed. Polymers in Aqueous Media. Washington, DC American Chemical Society, 1989, pp 1-28. 

Table V contains experimentally developed constants for water as the external phase fluid gelled with varying quantities of hydroxypropyl guar (HPG). The foam quality is 70%, but the effect of quality on the equation is minimal because of the density correction factor. Table V shows that water consistently produced higher results for X, b, and S. This result is indicative of the fact that gelled aqueous foam systems are drag-reducing fluids. Also in the gelled systems, the exponents b and S are identical, and this implies that the shear stress is a function of density and velocity only. Furthermore, X is approximately equal to S — 1, this relationship correlates density changes resulting from changes in foam quality or pressure.

Function in Formula Thickener, gelling agent for aqueous systems Use Concentration Use up to 20% in water Solubility Characteristics Soluble in water... 

Sawyer, Edgar W., "Use of Gelling Clays to StabUize Agricrdtural Pesticide Suspensions and Emulsions in Aqueous Systems", Special Technical Publication 943, pp 177-186, American Society for Testing and Materials, Philadelphia, Pennsylvania (1987). 

W. are a group of water-soluble or swellable, sometimes hydrogel-forming, RR-based (with a few exceptions) polymers, which act as - adhesives, binders, -+film formers, thickeners, gelling agents, suspension aids, crystallization inhibitors, emulsion stabilizers, protective colloids, or water absorbents by giving certain rheological properties to aqueous systems. 

As distinct from the gelling properties of certain natural gums, usually exhibited by structural rigidity, viscosity is a thickening of the aqueous portion of a system by means of particle water absorption, and swelling of the colloid. From a practical angle, it manifests itself by the phenomena of thickening and reduced flow characteristics. 

In particular. Table 17-2 reflects the complexity of a fracturing fluid formulation. Some additives may not be used together reasonably, such as oil-gelling additives in a water-based system. More than 90% of the fluids are water based. Aqueous fluids are economical and can provide control of a broad range of physical properties as a result of additives developed over the years. 

Jeong and coworkers have reported peptide-based thermo-gelling systems using PEG-b-polyAla as an injectable cellular scaffold [315]. The polymer aqueous solution undergoes sol-gel transition as temperature increases. The fraction of the p-sheet structure of the poly Ala dictated the population and thickness of fibrous nanostructure in the hydrogel, which affected the proliferation and protein... 

Of the various approaches taken while using a bi-component ink system, this is the most common one as reflected in the patent ht-erature (see Fig. 12). This system is based on the fact that several polymers are soluble in aqueous solution under certain conditions (e.g., pH value, presence or absence of metal ions) and will precipitate as soon as the chemical environment in the ink is changed. An acrylic polymer will be soluble in the ink at an elevated pH, hence it will instantaneously precipitate upon its reaction with a polyvalent cation which is present at the surface of the substrate. The result of this reaction will be a gelled ink droplet which will be practically immobilized. The schematic reaction mechanism is shown in Fig. 13. 

An alternative to the traditional O/W/O or W/O/W emulsions is the O/W/W format. The addition of a whey-protein oil-in-water stabilized emulsion to an aqueous two-phase system (comprising heat denatured whey protein and high methoxy pectin) resulted in the formation of such an emulsion. This was subsequently gelled with calcium ions. It has been suggested that these novel structures can provide both encapsulation and controlled release (Kim et al. 2006). 

---