Chemical gelation

The resultant formulation, in a liquid form, is dispersed into fine droplets by dripping (drop-by-drop), spraying, or emulsification. This step increases the liquid surface available for further transformations (evaporation, cooling, gelation, chemical reactions) and favors the generation of dispersed (liquid or solid) delivery structures. 

Kubo W. Kitamura T Hanabusa K. Wada Y Yanagida S. Quasi-solid-state dye-sensitized solar cells using room temperature molten salts and a low molecular weight gelator. Chemical Communication 2002, 374-375. 

An ink is considered dry when a print does not stick or transfer to another surface pressed into contact with it. Drying is accompHshed by one or more of the following physical or chemical mechanisms absorption, evaporation, precipitation, oxidation, polymerization, cold setting, gelation, and radiation curing. 

Theories of Gelation. The classical or mean field theory of polymeri2ation (4) is useful for visuali2ing the conditions for gelation. This model yields a degree of reaction, of one-third at the time of gelation for chemical species having functionaUty equal to four. Two-thirds of the possible... 

Polyelectrolyte complex membranes are phase-inversion membranes where polymeric anions and cations react during the gelation. The reaction is suppressed before gelation by incorporating low molecular weight electrolytes or counterions in the solvent system. Both neutral and charged membranes are formed in this manner (14,15). These membranes have not been exploited commercially because of then lack of resistance to chemicals. 

In addition to acting as impact modifiers a number of polymeric additives may be considered as processing aids. These have similar chemical constitutions to the impact modifiers and include ABS, MBS, chlorinated polyethylene, acrylate-methacrylate copolymers and EVA-PVC grafts. Such materials are more compatible with the PVC and are primarily included to ensure more uniform flow and hence improve surface finish. They may also increase gelation rates. In the case of the compatible MBS polymers they have the special function already mentioned of balancing the refractive indices of the continuous and disperse phases of impact-modified compound. 

In order to increase the capacity of a production line especially by reducing the necessary press times, adhesive resins with a reactivity as high as possible should be used. This includes two parameters (1) a short gelation time and (2) a rapid bond strength increase, and this even at a low degree of chemical curing. 

Consistent with their chemical differences, the molecular structures of i- and K-carrageenans are not identical. A shorter pitch and an offset positioning of the two chains in the kappa helix is compatible with the lack of sulfate group on every 3,6-anhydrogalactose residue. The variations in molecular structures mirror the types of junction zones formed by these polymers and relate to the observed gelation properties. 

Winter, H.H. Evolution of rheology during chemical gelation. Prog. Colloid Polym. Scl,15,104—110,1987. Hempenius, M.A. et al. Melt rheology of arborescent graft polystyrenes. Macromolecules, 31, 2299, 1998. 

Bode, H-J, The Use of Liquid Polyacrylamide in Electrophoresis III. Properties of Liquid Polyacrylamide in the Presence of Cellulose Acetate, Analytical Biochemistry 92, 99, 1979. Bowman, CN Peppas, NA, A Kinetic Gelation Method for the Simulation of Free-Radical Polymerizations, Chemical Engineering Science 47, 1411, 1992. 

Rombouts, F.M. and Thibault, J.F. (1986) Sugar beet pectins chemical structure and gelation through oxidative coupUng. In Chemistry and Function of Pectins, edited by M.L. Fishman, et al, pp. 49-60. American Chemical Society, Washington, DC. 

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