Nanoparticle compatibilization

Titania nanoparticles were first surface-modified with polybutylene succinimide diethyl triamine (OLOA370) [87-91] and then 5wt% of the hydrophobized material was dispersed in styrene prior to a miniemulsification process. About 89% of the titania could be encapsulated in 73% of the PS, but pure polystyrene particles were still detected. Another efficient compatibilizer for titania is Solsperse 32000, a polyamine/polyester. By modifying titania with this polymer, hybrid nanoparticles with PS and PS-co-polybutylacrylate(PS-co-PBA) could be generated [92-95]. 

The combination of experimental evidence and computational modeling show conclusively that stable, homogeneously blended (bulk-immiscible) mixed-polymer composites can be formed in a single microparticle of variable size. To our knowledge, this represents a new method for suppressing phase-separation in polymer-blend systems without compatibilizers that allows formation of polymer composite micro- and nanoparticles with tunable properties such as dielectric constant. Conditions of rapid solvent evaporation (e.g. small (<10 pm) droplets or high vapor pressure solvents) and low polymer mobility must be satisfied in order to form homogeneous particles. While this work was obviously focused on polymeric systems, it should be pointed out that the... 

A single-pot reaction of maghemite nanoparticles, fluorescent pigment, polyester resin, TweenSO, SpanSO, AIBN, and styrene dispersed in an aqueous NaOH solution, led to the formation of ferromagnetic (hysteresis in vibrating sample magnetometry analysis) hybrid nanoparticles [164]. Magnetite compatibilization is ascribed to the application of polyester resin. 

Immiscible polymer blends normally have a sea-island stmcture, where one polymer is dispersed as (normally spherical) particles in the other polymer, which forms the matrix, or a co-continuous structure, where both polymers are equally distributed in the blend without one polymer forming a continuous phase. For the blends to have good mechanical properties, it is also important that there is good interaction between the different components in the blend. To ensure this, researchers have tried a variety of methods to compatibilize the polymers in blends. The most used method is to add a third polymer, which interacts well with the other two polymers, into the blend. Reactive blending is another well-used method, and recently, a lot of investigation went into the use of (especially clay) nanoparticles to improve the interaction between the polymer components by locating themselves on the interfaces between the polymers. 

Theories that describe the reduction of the size of the dispersed phase in the presence of nanoparticles vary, depending on whether the filler is located in the continuous phase, in the dispersed phase, or at the interphase between the two blend components. Compatibilizing effects due to polymer adsorption on the filler surface, as well as reduction in the interfacial tension between the two phases in the presence of the filler, are the generally accepted mechanisms when the fillers are located at the interface [11,13,26]. Ray et al. [11] showed that upon addition of only 0.5 wt% of organically modified clay, the interfacial tension decreased from 5.1 to 3.4 mN/m for a PS/PP blend and from 4.8 to 1.1 mN/m for PS/PP-g-MA, suggesting a possible interfacial activity of the clay that is localized at the interface in similar fashion to classical compatibilizers. 

In the last decade, considerable progress was observed in the field of PO/compatibil-izer (predominantly on the base of PO-g-MA)/organo-surface-modified clay nanocomposites. Polyethylene (PE), polypropylene (PP), and ethylene-propylene (EP) rubber are one of the most widely used POs as matrix polymers in the preparation of nanocomposites [3,4,6,30-52]. The PO silicate/silica (other clay minerals, metal oxides, carbon nanotubes, or other nanoparticles) nanocomposite and nanohybrid materials, prepared using intercalation/exfoliation of functionalized polymers in situ processing and reactive extrusion systems, have attracted the interest of many academic and industrial researchers because they frequently exhibit unexpected hybrid properties synergisti-cally derived from the two components [9,12,38-43]. One of most promising composite systems are nanocomposites based on organic polymers (thermoplastics and thermosets). 

However, the simple melt mixing of polyolefins with natural clays, does not guarantee a sufficient level of dispersion of the nanoparticles, which are often present in the form of micron-size agglomerates. In order to overcome this problem, two main strategies have been followed surface functionalization of needle-like clays (usually by alkyl-silanes) or addition of a third polymeric phase (usually maleic anhydrite modified PP PP-g-MA), which acts as a compatibilizer between the matrix and nanofiller. Both methods tend to modify the surface energies of the nanocomposite system, in order to reduce the interparticle interaction and improve the dispersion. In the case of a reactive surface treatment only, the polymer-day interaction is expected to be enhanced, along with better nanoclay dispersion, which is very important for the final mechanical properties. 

The compatibilization strategies comprise (i) addition of a small quantity of cosolvent - a third component, miscible with both phases, (ii) addition of a copolymer whose one part is miscible with one phase and another with another phase, (iii) addition of a large amount of a core-shell copolymer - a compatibilizer-cum-impact modifier, (iv) reactive compounding that leads to modification of at least one macromolecular species that result in the development of local miscibility regions, and (v) addition of a small quantity of nanoparticles which influence blend structure similarly to particle-stabilized water/oil emulsions. 

Nowadays, nanoparticles have been widely used as fillers and compatibilizers. They exert certain effect on the miscibility of blends. Ginzburg applied a simple theory to study the effect of nanoparticles on the miscibility of PVA/PMMA blends and compared theoretical and experimental results for the same system with fillers and without fillers (Ginzburg 2005) when nanoparticle radius is smaller than polymer radius of g5n ation, the addition of nanoparticles increases the critical value of Xn and stabilizes the homogeneity (Fig. 10.38). 

The compoimding technology of PE blends has been expanded by the need for the addition of fillers, reinforcements, and nanoparticles, the latter treated as inorganic macromolecules that require compatibUization and dispersion. The reactive compatibilization in a TSE developed by the end of the 1980s revitalizing the academic and industrial interest in the mechanical compounding of blends. 

The first polymer blend was patented in 1846 and since then blends have became ubiquitous. Blending may provide a full set of material properties, improving processability and/or specific properties. With the advancement of technology there is the notorious growth of complexity - while in the beginning blending involved two polymers, initially without a compatibilizer, more recent commercial alloys have up to five polymers, three compatibilizers, and frequently are reinforced with macro- or nanoparticles [1]. 

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