Gelation factors affecting

Although a number of factors affect structural evolution in sol-gel processing, many of the observed trends can be explained on the basis of the stability of the M-O-M bond in its synthesis environment. Structures which form in solution are the products of a successive series of hydrolysis, condensation and restructuring reactions. M-0-M bonds which are unstable with respect to hydrolysis and alcoholysis are absent. In borates this criterion precludes gelation for systems with insufficient fractions of 4-coordinated borons. In silicates... 

The paper first considers the factors affecting intramolecular reaction, the importance of intramolecular reaction in non-linear random polymerisations, and the effects of intramolecular reaction on the gel point. The correlation of gel points through approximate theories of gelation is discussed, and reference is made to the determination of effective functionalities from gel-point data. Results are then presented showing that a close correlation exists between the amount of pre-gel intramolecular reaction that has occurred and the shear modulus of the network formed at complete reaction. Similarly, the Tg of a network is shown to be related to amount of pre-gel intramolecular reaction. In addition, materials formed from bulk reaction systems are compared to illustrate the inherent influences of molar masses, functionalities and chain structures of reactants on network properties. Finally, the non-Gaussian behaviour of networks in compression is discussed. 

May, C.D., Stainsby, G. (1986). Factors affecting pectin gelation. In Phillips, G.O., Wedlock, D.J., Williams, P.A. (Eds). Gums and Stabilisers for the Food Industry 3, London Elsevier Applied Science, pp. 515-523. 

Boye, ], Alii, ], Ramaswamy, H, and Raghavan, V, (1997), Interactive effects of factors affecting gelation of whey proteins. /. Food Sci. 62, 57-65,... 

The literature studies reported different factors affecting microcapsules preparation, such as concentration of alginate, hardening bath, gelation time, as weU as concentration of probiotic bacteria. 

The increasing size of the growing polymer molecules and the resulting morphology (stabilized by gelation in crosslinking polymerization) are the main factors affecting PIPS. The PIPS processes are influenced by thermodynamic and kinetic factors that can determine stable systems (where no phase separation is produced), metastable systems (when the phase separation may take place), or unstable systems (for which the phase separation does not take place). 

As can be seen from the above description, there are many variables involved in the phase-inversion technique. Among others the composition of the polymer solution, the solvent evaporation temperature and evaporation period, the nature and the temperature of the gelation media, and the heat treatment temperature are the primary factors affecting the reverse osmosis performance of the membrane. When polymers other than cellulose acetate are used, solvents and nonsolvent additives appropriate to prepare membranes from the particular polymer must be found. Depending on the combination of variables, membranes of different polymeric materials with different pore sizes can be prepared. 

The glass transition involves additional phenomena which strongly affect the rheology (1) Short-time and long-time relaxation modes were found to shift with different temperature shift factors [93]. (2) The thermally introduced glass transition leads to a non-equilibrium state of the polymer [10]. Because of these, the gelation framework might be too simple to describe the transition behavior. 

When tested in other polymers, maleimides did not affect the rate of cross-linking in polydimethylsiloxane, polyisobutylene, and polyvinylchloride. In polyethylene, the addition of 5 wt.% of m-phenylene dimaleimide increased the G(X) from 1.8 to 7.2. In the polyvinylacetate the effect was even more pronounced the dose for gelation was reduced by about a factor of 50. Contrary to the cross-link enhancing effect found for m-phenylene dimaleimide, cross-linking was retarded in polyvinyl acetate by the addition of monomaleimides. When analyzing the mechanism of the reaction it was concluded that monomaleimides are not expected to affect cross-linking in saturated polymers. ... 

While gelation temperature Is usually considered a characteristic property of a given protein system, the heating conditions required for gel formation may be Interrelated to all of the previously mentioned factors. It has been observed that WPG dispersions In 0.2 M NaCl will gel at 75 C while a temperature of 90 C Is required to gel WPG dispersions In distilled water (1). Heating time, at a specific temperature, required to form a protein gel structure Is generally considered to decrease with Increased protein concentration. Alteration of heat treatment conditions affects the gel s macroscopic and microscopic structural attributes. This has been dramatically shown by Tombs (A) with electromlcroscoplc evaluation of bovine serum albumin gels. 

The preparation of SiC>2 gel is not very complicated. Either the reaction of an appropriate amount of acid and silicate or the gelation of Si02 colloidal particles can result in Si02 gel. However, the preparation of Si02 gel with various properties is not that simple. Previous studies indicated that the particle size, porosity, and hardness of the Si02 gel strongly depended on the gelation rate that was affected by many factors.1111... 

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