Nucleation additive effect

If some or all of these variables have a large effect, nueleation/growth rates may be high the point of addition effect on mean particle size and PSD may be the most sensitive indicator of a high nucleation rate. 

The above description stresses either chemical reactions in these combinations or physical interactions between components. In reality there is still additional effect which may induce changes to structure and thus properties. It is a commonly known effect of fillers on the nucleation of polymers. It can be perceived that filler does not affect nucleation of both polymers with the same intensity. In addition, the availability of polymers at the interface with fillers depends on various parameters such as viscosity, acid/base interaction, etc. If these two are included in the number of combinations, there is a theoretical abundance of possible combinations and thus... 

The transition was found to be mediated by nucleation and traveling of sharp fronts (Fig. 11a) that indicates a backward bifurcation, although hysteresis has not been identified directly. Rather, a sharp jump in the contrast (pattern amplitude) with increasing voltage has been detected, with some indications that a low contrast pattern already arises at voltages before the jump occurs in Fig. 1 lb. A preliminary, weakly non-linear analysis has exhibited a bifurcation, which is in fact weakly supercritical at low frequencies. If small changes of the parameters and/or additional effects are included (e.g. flexoelectricity and weak-electrolyte effects) the bifurcation could become a more expressed subcritical one [32, 33]. 

Good solubility and diffusion of the nucleating agent in PVDF was noticed because the crystalhzation of the additive and the crystallization of PVDF on the additive surface was shifted to the right at short times.These observations show that the most effective nucleating additives will dissolve at low concentrations, dissolve completely at the polymer processing temperature, which takes care of their good dispersion in the polymer, and crystallize above crystalhzation temperature of polymer. 

Efficiency of nucleating additive ean also be measured by the size of spherulite, since it is added to decrease the spheralite size. " The other usefiil method eonsists of addition of small amount of nucleating agent (0.02 wt%) and observing its effect on increase of crystallization temperature. Nucleation efficiency was also estimated using the following equation ... 

The time evolution of / is is influenced by chemical and physical processes like particle growth, particle coalescence, particle nucleation, the effect of additional substances (e.g. catalyzers and emulsifiers) and the reaction conditions. For the more chemical and physical side of the quite complicated interplay of all these factors we refer to the papers mentioned in the introduction. 

DSC can be used to study additive nucleating activity and has revealed the effect of nucleating agents and pigments on the crystallisation of iPP [100]. Van Every et al. [101] have used DSC and factor analysis to detect trace amounts (up to 250 ppm) of the nucleator sodium benzoate (NaBz) in PP formulations. Also other authors [102] have used DSC to study crystal nucleating activity (effect of copper deactivator on ageing life of PP). 

Additives, whether hydrophobic solutes, other surfactants or polymers, tend to nucleate micelles at concentrations lower than in the absence of additive. Due to this nucleating effect of polymers on micellization there is often a measurable erne, usually called a critical aggregation concentration or cac, below the regular erne observed in the absence of added polymer. This cac is usually independent of polymer concentration. The size of these aggregates is usually smaller than that of free micelles, and this size tends to be small even in the presence of added salt (conditions where free micelles tend to grow in size). 

An increase in the time required to form a visible precipitate under conditions of low RSS is a consequence of both a slow rate of nucleation and a steady decrease in RSS as the precipitate forms. One solution to the latter problem is to chemically generate the precipitant in solution as the product of a slow chemical reaction. This maintains the RSS at an effectively constant level. The precipitate initially forms under conditions of low RSS, leading to the nucleation of a limited number of particles. As additional precipitant is created, nucleation is eventually superseded by particle growth. This process is called homogeneous precipitation. ... 

In addition to the nucleating agents discussed in Section 18.4, many other materials have been found to be effective. Whilst the nylons may be self-nucleating, partieularly if there is some unmelted crystal structure, seeding with higher melting point polymers can be effective. Thus nylon 66 and poly(ethylene terephthalate) are reported to be especially attractive for nylon 6. 

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