Hydration polymer glasses

From crystalline to amorphous (particle) hydrates inorganic polymers, glasses, clays, gels and porous media... 

AB cements are not only formulated from relatively small ions with well defined hydration numbers. They may also be prepared from macromolecules which dissolve in water to give multiply charged species known as polyelectrolytes. Cements which fall into this category are the zinc polycarboxylates and the glass-ionomers, the polyelectrolytes being poly(acrylic acid) or acrylic add copolymers. The interaction of such polymers is a complicated topic, and one which is of wide importance to a number of scientific disciplines. Molyneux (1975) has highlighted the fact that these substances form the focal point of three complex and contentious territories of sdence , namely aqueous systems, ionic systems and polymeric systems. 

Wilson, A. D., Crisp, S. Paddon, J. M. (1981). The hydration of a glass-ionomer (ASPA) cement. British Polymer Journal, 13, 66-70. 

The transport of many compounds takes place through interstices of polymer chains filled with aqueous medium [52], In such cases, the rate of mass transport is directly proportional to the degree of hydration of the membranes [53]. The most widely accepted method for determining the hydration of membranes is to equilibrate the membranes in water or buffer and weigh these membranes after blotting [54], In a newer method, the matrices to be studied are placed on a sintered glass funnel which is attached to a capillary filled with water. The absorption of water results in the movement of the capillary front [55],... 

With continuous development of systems for controlled drug release, new materials are being used whose influence on peptide stability must be carefully examined. Thus, the model hexapeptide Val-Tyr-Pro-Asn-Gly-Ala (Fig. 6.30) embedded in poly (vinyl alcohol) and poly(vinyl pyrrolidone) matrices had rates of deamidation that increased with increasing water content or water activity, and, hence, with decreasing glass transition temperature (Tg). However, the degradation behavior in the two polymers differed so that chemical reactivity could not be predicted from water content, water activity, or T% alone. Furthermore, the hexapeptide was less stable in such hydrated polymeric matrices than in aqueous buffer or lyophilized polymer-free powders [132],... 

Interfacial polymerization membranes are widely used in reverse osmosis and nanofiltration but not for gas separation because of the water-swollen hydrogel that fills the pores of the support membrane. In reverse osmosis, this layer is hydrated and offers little resistance to water flow, but when the membrane is dried for use in gas separation the gel becomes a rigid glass with very low gas permeability. This glassy polymer fills the membrane pores and, as a result, defect-free... 

Figure 7.10. Glass transition temperature versus moisture eontent of stareh subifactions measured by DSC with 3°C/min heating rate (Tg represents the values at the midpoint of the transition in the second scans) (Reprinted from Carbohyd. Polym., 32, Bizot, Le Bail, Leroux, Davy, Roger, and Buleon, Calorimetrie evaluation of the glass transition in hydrated, linear and branched polyanhydroglucose compounds, pp. 33-50, Copyright (1997), with permission from Elsevier.)...

Fine crystalline quartz or amorphous substances (gel, quartz glass, etc.) are used as one of initial components for the synthesis [19]. Depending on temperature, pressure, pH of the medium and the presence of salts, silica can exist in solution both as simple ions or molecules, and as more complicated polymer particles. Under normal conditions silica passes into solution in monomer form, as silicic acid Si(OH)4 at large pH, silicate ions SiOj - are formed. Monosilicic acid is a very weak acid however, at increased temperature its dissociation constant increases substantially. The amount of monomer form also increases with temperature. The dissolution of Si02 is due to hydration as well as to depolymerization. 

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