Nanoparticle/polymer/solvent solution

Figure 4.1 shows the schematic of solution processing. Nanoparticles are first dispersed in a solvent or polymer solution. The nanoparticle/polymer/ solvent solution is mixed by energetic agitation such as magnetic stirring,... 

The sol-gel process performed in low concentrated polymer-solvent solutions is another attractive route to develop hybrid membranes because it allows an in situ dispersion of metal-based nanoparticles within the polymeric matrix, achieving a suitable interfacial morphology between the continuous and the dispersed phase. Silica particles and polyimide have been frequently used to produce these hybrid membranes [107,108]. In general, hydrolysis and condensation reactions are involved in the sol-gel process, when alkoxides are involved in the formation of the dispersed phase. The advantage of using this method is the formation of an inorganic network largely interconnected with the polymeric materials mainly with noncovalent interactions [109]. In Fig. 7.10 a... 

In this technique, not only pure polymers can be electrospun, but also polymers in combination with nanoparticles, as realized for example with PLGA and HA nanoparticles [61,72]. Moreover, surfactants can be added to the nanoparticle-polymer-solvent mixture to facilitate the dissolution process and overcome the different polarities of hydrophilic nanoparticles snch as HA and the hydrophobic polymer-solvent solutions such as chloroform-dissolved PLA [55]. 

To prepare nanoparticles based on water-insoluble polymers, a solution of the polymer in an organic solvent can be emulsified within an aqueous phase. This O/W emulsion is then homogenized under high shear with an appropriate homogenization equipment... 

The use of a partly water-miscible solvent in which the drug and polymer is dissolved is shown in Scheme 5. An emulsion is formed on addition of the polymer-drug solution to an aqueous phase containing a stabilizer. Because of the partial miscibility of the first solvent, solvent diffuses from the dispersed droplets into the bulk to provide after some time polymer nanoparticles containing drug. 

In solution mixing, in order to overcome the limitations of melt mixing method, both the polymer and the nanoparticles are dissolved or dispersed in solution. This method enables modification of the particle surface without drying, which reduces particle agglomeration. After dissolvation the nanoparticle/ polymer solution can be cast into a solid, or solvent evaporation or precipitation methods can be used for isolation of nanoparticle/polymer composite. Conventional techniques can be used for further processing [Lee. E. S, 2004]. 

Electrospinning is an efficient technique for the fabrication of polymer fibers. Various cationic polymers have been successfully electrospun into ultrafine fibers, mostly from solvent solutions but some in melt form. Composite nanofibers of biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA) encapsulating chitosan/siRNA nanoparticles (NPs) were prepared by electrospinning (Figure 16.5). ... 

Nanoparticles can also be obtained from a polymer that has previously been prepared according to a totally independent method. The general principle is based on the solubility properties of the polymer. A diluted solution of the polymer is prepared and a phase separation is induced by addition of a non-solvent or by a salting-out effect. Once the proper conditions to form polymeric colloids are identified, the particles can be stabilised either by elimination of the polymer solvent by evaporation or by chemical cross-linking of the polymer. 

A series of works has been done in this field of growing interest for the purposes of improving the dispersibility of nanoparticles in solvents and their compatibility in polymers [25]. Mostly, the graft polymerization is conducted via two routes (1) monomers are polymerized from active compounds (initiators or comonomers). PMMA is a commonly used thermoplastic matrix for fibers, sheets, and particles. There have been several studies on PMMA-fiber composites prepared by in situ polymerization [26], solution mixing [27], or melt blending [28]. The last one is already an industrial process for fabricating carbon fiber-reinforced thermoplastic composites. 

Composite solutions or suspensions exploiting (i) mixtures of different solvents, (ii) blends of different polymer materials, (iii) low-molar-mass molecules as dopants or (iv) dispersed inorganic particles such as semiconductor or oxide nanocrystals are largely used in electrospinning. In particular, adding nanoparticles in the solution to be electrospun, together... 

The hydrogenation of latex polymer was accomplished using nanoparticle polymers in aqueous solution, without added solvent, and using Wilkinson s catalyst. The use of extremely small latex particles allows high reaction rates with lower catalyst concentrations, two green chemistry benefits. At 120 C, 1 wt % catalyst, and 35.3 nm particles, the data in Table 6.6 is reported. 

Xylan-based micro- and nanoparticles have been produced by simple coacervation (Garcia et al., 2001). In the study, sodium hydroxide and chloride acid or acetic acid were used as solvent and non-solvent, respectively. Also, xylan and surfactant concentrations and the molar ratio between sodium hydroxide and chloride acid were observed as parameters for the formation of micro- and nanoparticles by the simple coacervation technique (Garcia et al., 2001). Different xylan concentrations allowed the formation of micro- and nanoparticles. More precisely, microparticles were found for higher concentrations of xylan while nanopartides were produced for lower concentrations of the polymer solution. When the molar ratio between sodium hydroxide and chloride acid was greater than 1 1, the partides settled more rapidly at pH=7.0. Regarding the surfactant variations, an optimal concentration was found however, at higher ones a supernatant layer was observed after 30 days (Garda et al., 2001). 

Dendrimer-protected colloids are capable of adsorbing carbon monoxide while suspended in solution, but upon removal from solution and support on a high surface area metal oxide, CO adsorption was nil presumably due to the collapse of the dendrimer [25]. It is proposed that a similar phenomena occurs on PVP-protected Pt colloids because removal of solvent molecules from the void space in between polymer chains most likely causes them to collapse on each other. Titration of the exposed surface area of colloid solution PVP-protected platinum nanoparticles demonstrated 50% of the total metal surface area was available for reaction, and this exposed area was present as... 

Chemical reduction of metal salts in solution is the most widely used method of preparation of metal nanoparticles, especially in laboratories. In general, the reducing reagents are added into the solution of the precursor ions, but in some cases, a solvent works as a reductant. Various reducing reagents have been proposed to prepare metal nanoparticles. Ethanol or small alcohols can reduce precious metal ions such as Au, Pt", Pd, Ag, and so on [3j. Polymer-stabilized precious metal nanoparticles and their alloy particles can be used as good catalysts for various reactions. Polyols, such as ethylene glycol, were... 

---