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Gelation can occur either by physical linking or by chemical crosslinking. While the physical gels involve physical bonds, chemical gelation involves covalent bonds. The first quantitative theories of chemical gelation were formulated in the 1940s by Flory and Stockmayer. Critical percolation theory was successfully applied to gelation in 1970s.
In polymer chemistry, the gel point is an abrupt change in the viscosity of a solution containing polymerizable components. At the gel point, a solution undergoes gelation, as reflected in a loss in fluidity. After the monomer/polymer solution has passed the gel point, internal stress builds up in the gel phase, which can lead to volume shrinkage.
Flory–Stockmayer theory is a theory governing the cross-linking and gelation of step-growth polymers. [1] The Flory–Stockmayer theory represents an advancement from the Carothers equation, allowing for the identification of the gel point for polymer synthesis not at stoichiometric balance. [1]
Gelation time is the time interval between the onset of reaction– by heating, addition of catalyst into a liquid system, etc.– and gel point. Kinetic and statistical mathematical theories have had moderate success in predicting gelation parameters; a simple, accurate, and widely applicable theory has not yet been developed.
Mechanics of gelation describes processes relevant to sol-gel process. In a static sense, the fundamental difference between a liquid and a solid is that the solid has elastic resistance against a shearing stress while a liquid does not. Thus, a simple liquid will not typically support a transverse acoustic phonon, or shear wave. Gels have been ...
Random graph theory of gelation is a mathematical theory for sol–gel processes.The theory is a collection of results that generalise the Flory–Stockmayer theory, and allow identification of the gel point, gel fraction, size distribution of polymers, molar mass distribution and other characteristics for a set of many polymerising monomers carrying arbitrary numbers and types of reactive ...
The Stöber process is a well-studied example of polymerization of an alkoxide, specifically TEOS. The chemical formula for TEOS is given by Si(OC 2 H 5) 4, or Si(OR) 4, where the alkyl group R = C 2 H 5. Alkoxides are ideal chemical precursors for sol–gel synthesis
Silica gel was in existence as early as the 1640s as a scientific curiosity. [5] It was used in World War I for the adsorption of vapors and gases in gas mask canisters.The synthetic route for producing silica gel was patented in 1918 by Walter A. Patrick, a chemistry professor at Johns Hopkins University.