Nucleation retardation, mechanism

MC) and HPMC could significantly inhibit the crystallization of supersaturated hydrocortisone acetate (HA). The mechanism of nucleation retardation was believed to be due to the hydrogen bonding interactions between HA and the polymers. As to the... 

Crystallization from Aqueous Solutions. Pure water can freeze very fast after nucleation has occurred, because there is virtually no retardation mechanism acting. The freezing of water is exceptional in that it goes along with an increase in volume rather than a decrease. The physical properties of water show a number of anomalies at low temperature. 

In this Chapter, thermal analysis of the decomposition process has been performed -hence, the flame retardancy and thermal stabihzation of halogenated and non-halogenated polyester resins by ZHS may be explained by the formation of smface-localized spherical barriers which are growing according to the nucleation growth mechanism and which attenuate the transfer of heat from the decomposition zone to the substrate. This effect was foimd as dominating in the flame-retardancy mode of action. 

The foreign species act in solution and usually retard nucleation or growth of goethite by competing with soluble Fe " species for sites on the subcritical nucleus or on the growing crystal. This mechanism is independent of the presence of ferrihydrite. 

The stabilizer may consist of carboxylic acids and phosphorus-containing organic acid salts such as hexametaphosphates, polyphosphates and phosphonates. The mechanism of action of the stabilizer admixture is thought to be related to the inhibition of CSH and CH nucleation. It is claimed that the nucleation process is controlled more comprehensively than that obtained with conventional retarders [10], Cement hydration is arrested by the admixture acting on all phases of cement hydration including the C3A fraction. The claim is... 

Reimers [95] used polymeric costabihzer to carry out miniemulsion polymerization of MMA. Droplet nucleation was found to be the dominant nucleation mechanism in the polymerization. As a result, the nucleation was more robust, and the polymerizations were less sensitive to variations in the recipe or contaminant levels. This was evident in the rates of polymerization and in the particle numbers. The miniemulsion polymerizations were subjected to changes in initiator concentration, water-phase retarder, and oil-phase inhibitor, and were shown to be significantly more robust. 

Commercial polyolefins often contain additives such as colorants, flame retardants, antioxidants, light stabilizers, nucleating agents, antistatic agents, lubricants (microcrystalline waxes, hydrocarbon waxes, stearic acid, and metal stearates), and so on. These additives aid the processing and fabrication of products from polyolefins. Detailed treatments about specific polyolefins, polymerization systems/ mechanism/processes, structures, properties, processing, and applications may be found in References 2-9. 

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