Hybrid dispersion system

If a comparison were made between hybrid dispersion systems taking into account the kind of dispersion particles they contain, it would appear that the best properties should generally be observed for systems obtained by synthesis for which the particles have a uniform structure (they may be called true hybrid particles) and the worst - for simple blends of the two dispersions [14] (see Figure 6.1). 

Figure 6.1 Comparison of hybrid dispersion systems obtained by (a) blending, (b) and (c) by synthesis, taking into account particle type.

J. Kozakiewicz, Hybrid Dispersion Systems as Coating Binders, Presented at the Seminar of Polifarb Cieszyn-Wroccaw, 9.05.1998, Ustron-Zawodzie. 

Homogeneity of dispersion and the homogeneous nature of the hybrid ORMOSIL systems result in intensely coloured films even at low thickness. Compared to organic polymers, the coloured hybrid films have enhanced mechanical properties such as greater hardness and stronger abrasion resistance. With respect to inorganic sol-gel films, hybrid films also have several advantages such as much better adhesion,... 

More recent efforts have focused on developments that create true hybrids. For example, blocked isocyanate prepolymers have been mixed with epoxy resins and cured with amines [68-70]. These blocked prepolymers will react initially with the amines to form amine-terminated prepolymers that cross-link the epoxy resin. Several blocked isocyanates are commercially available. The DESMOCAP (Bayer) llA and 12A products are isocyanates (believed to be blocked with nonylphenol) used as flexibilizing agents for epoxy resins. ANCAREZ (trademark. Pacific Anchor, Inc.) 2150 is a blocked isocyanate epoxy blend used as an adhesion promoter for vinyl plastisols. A one-package, heat-cured hybrid adhesive was reported consisting of isophorone diisocyanate, epoxy resin, and a dispersed solid curative based on the salt of ethylenediamine and bisphenol A [71]. Urethane amines are offered commercially that can be used with epoxy resins to develop hybrid adhesive systems [72]. 

When the process is carried out according to Method la it may be assumed that the kind of initiating system (water-soluble initiator or redox system) does not have any significant effect on the morphology of hybrid dispersion particles since the polymerisation proceeds mainly on the surface of DPUR particles and monomer droplets and in the micelles of emulsifier. In the case of water-soluble initiator (potassium persulphate) the polymerisation starts in water where the ion-radicals are formed from the monomer molecules dissolved in water. These ion-radicals can diffuse to DPUR particles, monomer droplets and emulsifier micelles. After this happens the system will consist of ... 

Method of Hybrid Dispersion Synthesis and Kind of Initiating System... 

The results of investigations of the effect of method of hybrid dispersion synthesis (la, lb, 2 or 3 - see Section 3.2) on the properties of dispersions as well as of films and coatings made from them are presented in Tables 6.9 to 6.11 (dispersions prepared using water-soluble initiator) and in Tables 6.12 to 6.14 (dispersions prepared using redox initiating system). In all dispersions the chemical structure of the polyurethane-urea and acrylic/styrene polymer component was the same (see relevant tables in Section 6.5.2). All the dispersions contained a similar low level (2-3.6%) of NMP. 

Investigations of swelling of DPUR particles with monomers indicate that although all monomer being fed into the system may theoretically enter DPUR particles, since the maximum degree of swelling is more than twice that of the monomer/ DPUR solids w/w ratio used commercially in synthesis of hybrid dispersions, in practice there will always be a natural tendency of the system to reach equilibrium between monomer droplets, non-swollen DPUR particles and swollen DPUR particles. Therefore, when hybrid dispersions are prepared according to method la, lb or 2 (see Section 6.3.2) the result will always be a mixture of particles of hybrid structure with DPUR and ASD particles, as has been explained in Section 6.3.2.1). 

A synergistic effect was also found between clay and CB N330 from Cabot, in NR based nanocomposites prepared by emulsion compounding.It was observed that both fillers were dispersed at nanoscale and randomly in the NR matrix the space between the clay layers was filled with CB particles. The mechanical properties of the nanocomposites, such as moduli at 100% and 300% elongation, tensile strength and tear strength were much improved, at the same total filler level, by the hybrid filler system, with respect to composites containing only one filler. 

The sectional quadrature method of moments (SQMOM) represents a hybrid between the sectional method and the quadrature method of moments (QMOM) and was proposed by Attarakih et al. [10] in order to solve the PBE for poly-dispersed systems. The novel idea is based on the concept of primary and secondary particles, where the former is responsible for distribution reconstruction while the latter is responsible for different particle interactions such as breakage and coalescence. 

According to a recent study, the commercially available LC systems can be classifled in three groups (1) optimized systems for fast separation with very low dispersion (crv,ext < 0 P-L ) (2) hybrid LC systems recommended for both fast and conventional separations ((Tv,ext = 10-30 p-L ) and (3) conventional LC systems with an extra-column variance over 50 pL (Figure 5.5). These major differences in extracolumn peak variance have a significant impact on measured column performance and achievable analysis time (63). Further improvements in instrument design (smaller dispersion) are necessary to take the full advantage of the most recent very efficient small columns. Today it is not always possible to utilize the potential of these small columns. The loss in efficiency can reach 30%-55% with commercially available optimized UHPLC systems (63). 

Clays have long been used as fillers in polymer systems because of low cost and the improved mechanical properties of the resulting polymer composites. If all other parameters are equal, the efficiency of a filler to improve the physical and mechanical properties of a polymer system is sensitive to its degree of dispersion in the polymer matrix (Krishnamoorti et ah, 1996). In the early 1990s, Toyota researchers (Okada et ah, 1990) discovered that treatment of montmorillonite (MMT) with amino acids allowed dispersion of the individual 1 nm thick silicate layers of the clay scale in polyamide on a molecular. Their hybrid material showed major improvements in physical and mechanical properties even at very low clay content (1.6 vol %). Since then, many researchers have performed investigations in the new field of polymer nano-composites. This has lead to further developments in the range of materials and synthesizing methods available. 

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