Crystallization, inhibition

As far as hydride decomposition is concerned, the relations are reversed. The larger the metal crystals are the slower their hydride decomposes (62). Moreover some deposits situated on the exit points of dislocations, for example on the surface of a nickel hydride crystal, inhibit hydrogen desorption and result in prolonging the hydride existence in the crystal (87). 

Khougaz, K. and S. D. Clas. 2000. Crystallization inhibition in solid dispersions of MK-0591 and poly(vinylpyrrolidone) polymer. J Pharm S89 1325-1334. 

ASD including the use of in silico solubility parameter (5) calculation (Ghebremeskel et al. 2007), Flory-Huggins (F-H) interaction parameter calculation (Marsac et al. 2006b Zhao et al. 2011), drug-polymer thermodynamic phase diagrams prediction (Tian et al. 2013), crystallization inhibition with molecular dynamic calculation (Pajula et al. 2012), etc. However, in spite of their use and popularity, these theoretical methods have limitations and lack predictability, reliability, and thereby have limited utility. 

Acidic Nil groups ElOO PVP PVPVA As for the carboxylic acids, the best crystallization inhibiting performance was obtained for polymers containing strong acceptor groups that provide a competitive hydrogen bond alternative for the acidic N-H group... 

Alcohols ElOO PVP PVPVA As the OH group acts as a strong donor and medium acceptor, polymers with strong acceptors would be expected to compete successfvilly for these donors. Indeed, the polymers having strong acceptors showed the best results in terms of crystallization inhibition... 

Kamachi AA, De Hon RA, Khan MA (1995) Compression of indomethacin coprecipitates with polymer mixtures effect of preparation methodology. Drug Dev Ind Pharm 21 1473-1483 Khougaz K, Clas SD (2000) Crystallization inhibition in solid dispersions of MKaL10591 and poly (vinylpyrrolidone) polymers. J Pharm Sci 89 1325-1334... 

Li and co-workers [63] studied the crystallisation and melting behaviour of poly(]3-hydroxybutyrate (P-HB)-co-P-hydroxyvalerate (P-HV)) and a blend of poly(P-HB-co-P-HV)/polypropylene carbonate (30/70 w/w) using DSC and FT-IR spectroscopy. Transesterification occurred between poly(P-HB-co-P-HV) and polypropylene carbonate during the melt blending process. During crystallisation from the melt, the crystallisation temperature of the blend decreased by 8 °C compared with that of neat poly(P-HB-co-P-HV) and the melting temperature decreased by 4 °C. This indicated that the presence of polypropylene carbonate reduced the perfection of the poly(P-HB-co-P-HV) crystals, inhibited by the crystallisation of poly(p-HB-co-P-HV) and weakened its crystallisation ability. The equilibrium melting temperatures of... 

The most critical decision a polymer scientist has to take, in addition to the always present consideration of cost constraints, is how to balance in his new molecule idea the several factors given above Does he need to maximize sequestration, trying to also obtain a good clay dispersion, which may be at the expense of the fabric s anti-incrustation performance Or should he not maximize the crystal inhibition performance of the polymer, in order to try to get a good fabric anti-incrustation also, and leave both the clay dispersancy and the prevention of soil redeposition to a bare minimum The answer to those questions obviously depend largely on the specific application considered and from... 

We have already seen that polymers can adsorb on cotton surfaces during the wash. They can also adsorb on insoluble salt precipitates, which are detrimental to a good wash end result. In this second case, the adsorption may be similar to the first case, but the considered surface is a crystal seed (i.e., a nucleus which is expanding in size as insoluble matter in the liquid phase due to the current thermodynamic conditions. Once again, the polymer is anchored on the surface by its active groups, but the mechanism in operation in this case is the one of crystal distortion and consequent crystal inhibition. As stated in Ref. 2 ... 

If we now postulate that the mechanism of crystal inhibition is related to the hindering of the growth of agglomerates to their critical size, we can say that this will happen if one or more poljmaer molecules can diffuse into the volume Vi and reach the then subcritical agglomerate faster than the molecules of the dissolved salt present in the same volume. One possible use of the equation is therefore to calculate the concentration of the polymer needed in the solution to stop the nuclei from growing, once the diffusion coefficients are known or measured and die concentrations of the scaling salts are also known. 

Turbidity measurements support this conclusion (the lower the turbidity, the better the crystal inhibition) (Fig. 5). 

It can be seen that the long copolymer is able to act as crystal inhibitor for calcium carbonate only at very low temperatures (around 20°C). As soon as the wash temperature is raised to 40°C, there is no longer a crystal inhibition action, and at higher temperatures, the amount of precipitate even increases respect to the case of no polymer at all The polymer itself precipitates as bridging flocculant or, partially, as insoluble calcium salt. 

Figure 8 Crystal inhibition synergism polymers/phosphonates. (From Ref. 3.)...

The two monocomponent builder systems (polymer alone or zeolite alone) are very poor in performance. This is not a surprise because we have already clarified that a builder is more than just a chemical able to sequester ions or a chemical able to suspend soil. A builder needs to deliver significant performance in several areas, from sequestration, to soil suspension, to crystal inhibition to alkalinity buffering neither the zeolite alone nor the polymer alone can perform all these tasks. 

Short homopolymers of acrylic acid (particularly in the range of 2000—4500 molecular weight) are superior to long-chain pol3aners and copolymers. Crystal inhibition and dispersion (typical of the short-chain polymers) are more important in the automatic dishwashing formulations than sequestration (typical of long-chain copolymers). 

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