Nucleating effects

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). 

The greater the undercooling, the more rapidly the polymer crystallizes. This is due to the increased probability of nucleation the more supercooled the liquid becomes. Although the data in Fig. 4.8 are not extensive enough to show it, this trend does not continue without limit. As the crystallization temperature is lowered still further, the rate passes through a maximum and then drops off as Tg is approached. This eventual decrease in rate is due to decreasing chain mobility which offsets the nucleation effect. 

In Figure 13 the relation between the intrinsic coercivity and the particle diameter dis given. The figure is based on a described model (35). The maximum is found around the critical particle diameter. In general the particle diameter and size is not very well defined. For the multidomain particles (d > ) the is smaller than the intrinsic anisotropy field of the particle. Nucleation effects cause a decrease in as the increases. This behavior is... 

Several block copolymer systems have shown only domains I and III upon self-nucleation. This behavior is observed in confined crystallizable blocks as PEO in purified E24EP57EO1969 [29]. Crystallization takes place for the PEO block at - 27 °C after some weak nucleating effect of the interphase. Domain II is absent and self-nucleation clearly starts at Ts = 56 °C when annealed crystals are already present, i.e., in domain III (Fig. 17b). The absence of domain II is a direct consequence of the extremely high... 

In the case of PETP attention must be paid to the nucleating effect of the organic pigments, depending on the application (bottles). 

Its main field of application is in plastics. 1/3 SD HDPE samples, both transparent and opaque, withstand exposure to 300°C for 5 minutes, while 1/25 SD specimens are heat stable up to 250°C. Temperatures in excess of this value shift the shade towards more yellowish hues. P.O.64 does not have a nucleating effect on its medium, i.e., it does not affect the shrinkage of partially crystalline injection-molded polymers. 

The structure of crystalline polymers may be significantly modified by the introduction of fillers. All aspects of the structure change on filling, crystallite and spherulite size, as well as crystallinity, are altered as an effect of nucleation [9]. A typical example is the extremely strong nucleation effect of talc in polypropylene [10,11], which is demonstrated also in Fig. 2. Nucleating effect is characterized by the peak temperature of crystallization, which increases significantly on the addition of the filler. Elastomer modified PP blends are shown as a comparison crystallization temperature decreases in this case. Talc also nucleates polyamides. Increasing crystallization temperature leads to an increase in lamella thickness and crystallinity, while the size of the spherulites decreases on... 

Marosi, G., Anna, P., Balogh, I., Bertalan, G., Tohl, A., and Maatoug, M. A. 1997. Thermoanalytical study of nucleating effects in polypropylene composites. 3. Intumescent flame retardant containing polypropylene. Journal of Thermal Analysis 48 717-26. 

Polymerization is influenced by the physical structure and phase of the monomer and polymer. It proceeds in the monomer, and the chemical configuration of the macromolecules formed depends on whether the monomer is a liquid, vapor, or solid at the moment of polymerization. The influence of structural phenomena is evident in the polymerization of acrylic monomer either as liquids or liquid crystals. Supermolecular structures are formed in solid- and liquid-state reactions during and simultaneously with polymerization. Structural effects can be studied by investigating the nucleation effect of the solid phase of the newly formed polymer as a nucleation reaction by itself and as nuclei for a specific supermolecular structure of a polymer. Structural effects are demonstrated also using macromo-lecular initiators which influence the polymerization kinetics and mechanism. 

Addition of starch has a nucleating effect, which increases the rate of crystallisation. The rheology of starch/PCL blends depends on the extent of starch granule destruction and the formation of thermoplastic starch during extrusion. Increasing the heat and shear intensities can reduce the melt viscosity, but enhance the extrudate-swell properties of the polymer. 

Figure 9.10 Nucleation effect of branched polyethylene Mw, 6770 dispersity, 0.89 branches per molecule, 1.21 degree of crystallinity, 48% (a) 0%, (b) 0.05%, (c) 0.2% polyethylene...

---