Nanometric dispersions of particles and polymers

Equation of State for Nanometric Dispersions of Particles and Polymers... 

In order to obtain good interfacial adhesion and mechanical properties, the hydrophilie elay needs to be modified prior to its introduction in most polymer matriees, which are organophilie. When nanometric dispersion of primary clay platelets is obtained, the aspect ratio of the filler particle is increased and the reinforcement effect is improved [75-25],... 

The exfoliated system is almost always quoted as the most desirable, since nanometric dispersion of day platelets maximizes the interfacial region between the filler and the polymer matrix, thus allowing to exploit the excellent mechanical properties of the individual day layers. Moreover, when exfoliation is attained, the number of reinfordng components is dramatically increased, since each day particle contains a very large number of day sheets. To further complicate matters, often a mixed dispersion is observed for day with different populations of tactoids or with partial exfoUation of single layers. Transmission electron microscopy (TEM) and WAXD are by far the most employed characterization techniques that assess the morphology of PLSN. 

Polymer Colloids is a generic term encompassing all stable colloidal dispersions of polymers in aqueous or non-aqueous media for which the polymer particle size may be conveniently expressed in nanometres. For almost all synthetic and naturally-occurring polymer colloids the mean particle size falls in the 100-2000 nm range, but most commonly is 100-500 nm. 

Emulsions and suspensions are disperse systems that is, a liquid or solid phase is dispersed in an external liquid phase. While emulsions are sometimes formulated from oily drugs or nutrient oils their main function is to provide vehicles for drug delivery in which the drug is dissolved in the oil or water phase. Suspensions, on the other hand, are usually prepared from water-insoluble drugs for delivery orally or by injection, usually intramuscular injection. An increasing number of modern delivery systems are suspensions - of liposomes or of polymer or protein microspheres, nanospheres or dendrimers, hence the need to understand the formulation and stabilization of these systems. Pharmaceutical emulsions and suspensions are in the colloidal state, that is where the particles range from the nanometre size to visible (or coarse) dispersions of several micrometres. 

In this chapter, two new approaches for the synthesis of metal-polymer nanocomposite materials have been described. The first method allows the preparation of contact-free dispersions of passivated gold clusters in polystyrene, and it is based on a traditional technique for the colloidal gold synthesis—that is, the alcoholic reduction of tetrachloroauric acid in presence of poly(vinyl pyrrolidone) as polymeric stabilizer. The primary function of the stabilizer is to avoid cluster sintering, but it also allows us to isolate clusters by co-precipitation. It has been found that the obtained polymer-protected nanometric gold particles can be dissolved in alkane-thiol alcoholic solutions to yield thiol-derivatized gold clusters by thiol absorbtion on the metal surface. Differently from other approaches for thioaurite synthesis available in the literature, this method allows complete control over the passivated gold cluster structure since a number of thiol molecules can be equivalently used and the... 

Dispersion of nanometric particles and adsorbing polymers behave like reversible 2-component systems (A-B-solvent). Under conditions where attractions overcome repulsions there is a phase separation into a gel and a supernatant which have nearly the same polymer/particles ratio. Concentrate gels can be made easily through phase separation in the 2-phases region however 3iey are full of voids. These voids have been eliminated through compression and the equations of state of gels with different polymer/particles ratio have bwn determined. 

In the large field of nanotechnology, polymer-based nanocomposites have become a prominent area of current research and development for biomedical applications.In principle, nanocomposites are an extreme case of composite materials in which interface interactions between the two phases, the matrix and the reinforcement, are maximized. In the literature, the term nanocomposite is used for polymers with sub-micrometre dispersions. In polymer-based nanocomposites, nanometre sized particles of inorganic or organic materials are homogeneously dispersed as separate particles in a polymer matrix. Researchers have tried a variety of processing techniques to obtain dense polymer nanocomposite films. The incorporation of nanostructures into polymers can generally be done in different ways as indicated below ... 

Figure 84 Schematic representation of mechanisms and basic reagents of a mini emulsion polymerization process. The snrfactant and co-stabilizer stabilize the nanometric droplets, which act as polymerization nanoreactors, consequently producing polymer particles with approximately an equal size to the initial monomer droplets (50-500nm). The polymer particles are obtained from the nanoreactors formed from a dispersion procedure, in which micrometric droplets were ruptured by the use of high-energy processes.

In this chapter we review the effects of hydrated and anhydrous alumina as filler on FR properties of polymer nanocomposites. Nanocomposites are particle-filled polymers for which at least one dimension of the dispersed particles is in the nanometer range. In the following sections, the mechanism and mode of action of nanometric alumina trihydrate (ATH), alumina monohydrate (AlOOH), and alumina (AI2O3) will be discussed. 

Nanolillers are playing an increasingly important role in the field of rubbers. They can be dispersed as individual particles in the polymer matrix, with at least one dimension at the nanoscale, defined of the order of 100 nm or less . The nanometric size implies features such as a large specific surface area and, as a consequence, a large interfacial area with the polymer matrix. 

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