Polymer-silica nanocomposite

Hybrid polymer silica nanocomposites formed from various combinations of silicon alkoxides and polymers to create a nanoscale admixture of silica and organic polymers constitute a class of composite materials with combined properties of polymers and ceramics. They are finding increasing applications in protective coatings (Figure 7.1), optical devices, photonics, sensors and catalysis.1... 

Although PMOs and related materials have many potential applications, including adsorbants,49,50 sensors,51 and catalysts,52,53 we focus here on two specific classes of functional materials, nanovalves and polymer-silica nanocomposites formed via the co-assembly of hybrid precursors (or polymer-monomer species) with surfactant mesophases. 

In the second approach to self-assembly of polymer-silica nanocomposites, polymerizable surfactants are employed both to direct self-assembly into ordered mesophases and to serve as organic monomers which can be subsequently polymerized. For instance, Brinker et al. developed nonionic surfactants incorporating diacy-telene groups which could be polymerized upon irradiation by UV light.68 69 Similarly, poly(thiophene)70 and poly(pyrrole)71 have been successfully integrated into silica nanostructures in this manner. Importantly, this in situ polymerization produces isolated molecular wires, rather than clustered bundles of conductive polymer.70... 

Kawashima, D., Aihara, T., Kobayashi, Y., Kyotani, T., and Tomita, A. Preparation of mesoporous carbon from organic polymer/silica nanocomposite. Chem. Mater. 12, 2000 3397-3401. 

Garnweitner, G., Smarsly, B., Assink, R., Ruland, W., Bond, E., and Brinker, C. J. Self-assembly of an environmentally responsive polymer/silica nanocomposite, JACS (2003), 125, 5626-5627. 

Giannelis, E. P., Krishnamoorti, R., and Manias, E., Polymer/silica nanocomposites Model systems for confined polymers and polymer brushes, Adv. Polym. Sci. (1999), 118, 108-147. 

Percy and coworkers [39,40] synthesized colloidal dispersions of polymer-silica nanocomposite particles by homopolymerizing 4-vinylpyridine or copolymerizing 4-vinylpyridine with either methyl methacrylate, styrene, n-butyl acrylate or n-butyl methacrylate in the presence of fine-particle silica sols using a free-radical in aqueous media at 60°C. No surfactants were used and a strong acid-based interaction was assumed to be a prerequisite for nanocomposite formation. The nanocomposite particles had comparatively narrow size distributions with mean particle diameters of 150-250 nm and silica contents between 8 and 54 wt.%. The colloidal dispersions were stable at solids contents above 20 wt.%. 

Priestley, R. D., Rittigstein, P., Broadbelt, L. J., Fukao, K., and Torkelson, J. M., Evidence for the molecnlar-scale origin of the snppression of physical ageing in confined polymer fluorescence and dielectric spectroscopy studies of polymer-silica nanocomposites, /. Phys. Condens. Matter, 19, 205120-1 to 205120-12 (2007b). 

To date, silica has been the focus of the majority of studies on oxide-based nanos-tructured materials. One of the major reasons for this is its easy processability, high chemical inertness and exceptional colloidal stability. Moreover, silica can be processed as a thin film with controllable porosity and optical transparency. All these properties make silica ideal for use in model systems, and it is widely used in many industrial areas ranging from paints and drug delivery to composite materials. Zou et al. have recently published a detailed review on the preparation, characterization, properties, and applications of polymer/silica nanocomposites and the reader is referred to this review for in-depth description of the various synthetic routes [16]. 

Disulfide PEGDA Polymer silica nanocomposite Gold nanoparticles, CMHA-S, gelatin-DTPH... 

Commonly the term "hybrids" is more often used if the inorganic units are formed in situ by the sol-gel process ( Kickelbick, 2007).Meanwhile, use of the word "nanocomposites" implies that materials consist of various phases with different compositions, and at least one constituent phase (for polymer/silica nanocomposites, that phase is generally silica) has one dimension less than 100 nm. A gradual transition is implied by the fact that there is no clear borderline between "hybrids" and "nanocomp)osites"( Kickelbick, 2007). 

Zou, H., Wu, S., and Shen, J. 2008. Polymer/silica nanocomposites Preparation, characterization, properties, and applications. Chemical reviews 108 3893-3957. 

Polymer-silica nanocomposites thus prepared are characterized by electron microscopy, scattering techniques, nuclear magnetic resonance spectroscopy, etc. to determine the structiual features. In additimi, properties such as mechanical, thermal, optical, and other important physical properties are generally determined. 

Scheme 1.1 Three general approaches to prepare polymer/silica nanocomposites.

Proton exchange membranes The proton exchange membrane (PEM) is one of the major components in solid-type fuel cells, such as in PEM and direct methanol fuel cells. Up to now many research groups have reported the fabrication of polymer/silica nanocomposites as a PEM. 

Figure 4.31 Typical bright-field (a,c) and en-ergy-filtered (25 eV b,c) transmission electron micrographs obtained for the polymer/ silica nanocomposite particles (scale bar 100 nm). The top images show a core-sheir -type morphology for polystyrene/silica...

Other studies on polymer-silica nanocomposites are reviewed in Table 3.11. 

Considerable attention has also been paid in recent years to hybrid polymer-silica nanocomposites prepared mostly via a sol-gel process [219,243-254] where 10-100 nm size 3D silica domains (clusters) were covalently bound to the polymer. Polymers deprived of groups reactive in the sol-gel process but prone to hydrogen bonding with silanols of silica nanoparticles have also been successfully incorporated into nanophase-separated hybrid materials [246,248-252]. Some polymer-silica nanocomposites, in particular silica core-polymer shell nanoparticles [255-258], were prepared using 3D fumed silica nanoparticles. 

Contrary to the majority of papers on polymer-silica nanocomposites, the very low content of 3D nanosilica particles in the polymer matrix in this work resulted in average inter-particle distance L larger by an order of magnitude than the radius of gyration Rq of PHEMA. In spite of that, a considerable impact of small 3D silica additives on matrix dynamics was found due to double PU/PHEMA and silica/matrix hybridization. 

G. Nelson, R. Yngard, and F. Yang, Flammability of polymer-clay and polymer-silica nanocomposites. Journal of Fire Sciences, 23 (2005), 209-26. 

Nelson, G.L. Yngard, R. Yang, F. Flammability of polyma--clay and polymer-silica nanocomposites. J. Fire Sci. 2005, 23, 209-226. 

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