Gelation external

Water-soluble polymers (qv) can increase the viscosity of the foam external phase. This improves foam stabihty and reduces mobihty. Gelation of... 

The role of the ammonium salt anion is not the loading of the amphipathic weak base per se, but rather to control the stability of loading and the profile and rate of release of the amphipathic weak base from the liposome to the external aqueous phase. Two major factors that differentiate the different anions are, firstly, their ability to induce precipitation/crystallization/ gelation in the intraliposome aqueous phase (1,12), and secondly, their effect on the membrane/buffer and octanol/buffer partition coefficient of the amphipathic weak base (1). Regarding the precipitation, the higher the amount of precipitated amphipathic weak base, the more stable is the loading and the slower is its release rate (10-12,18,33,35) and (Wasserman et al.). There are also some risks involved in the precipitation which in some cases reduce the mechanical stability of the liposomes and change liposome shape (36). 

Chemistry is fundamentally important for the emergence of the new molecular designs and synthetic schemes that will underpin the development of molecules that are better able to transduce external stimuli into a reversible change in viscosity, even to the point of gelation. Some of the most successful approaches in this field employ the use of photochemistry. 

Flow imparts both extension and rotation to fluid elements. Thus, polymer molecules will be oriented and stretched under these circumstances and this may result in flow-induced phenomena observed in polymer systems which include phase-changes, crystallization, gelation or fiber formation. More generally, the Gibbs free energy of polymer blends or solutions depends under non-equilibrium conditions not only on temperature, pressure and concentration but also on the conformation of the macromolecules (as an internal variable) and hence, it is sensitive to external forces. 

In the case of crystals, one usually encounters structures that are anisotropic on a molecular scale, due to anisotropic interactions between the molecules. Clusters formed by colloidal-scale particles often do not exhibit anisotropy due to the isotropic character of the interactions on that colloidal scale. One may introduce anisotropy in that case by applying an external field, for example, a flow field or electric-magenetic field, and subsequently freezing the morphology by, for example, gelation. 

Figure 9(c). Sphere preparation by external gelation. (After Ref. 6.)... 

Silica in the form of thin films as well as oxide monoliths, fibers, and powders can be prepared from sol-gel method. In contrast with the fabrication of conventional inorganic glasses at much higher melting temperature, sol-gel processing is performed at low temperatures to produce oxide materials with desirable hardness, optical transparency, chemical durability, tailored porosity, and thermal resistance. The sol-gel method involves formation of a colloidal suspension (sol) and gelation to form a network in a continuous liquid phase (gel). One starts with an aqueous solution containing oxides or alkoxides, mutual solvent, and catalyst. Usually an external catalyst is added like mineral acids and ammonia as well as acetic acid, KOH, amines, KF, and HF for rapid and... 

Swelling, Drug Release. - Gelation of alginate by external Ba " (or other... 

---