Polymer/sol-gel composites

Figure 13.1. Mackenzie s three models for Class II polymer/sol-gel composites. From left to right Model I, Model 2, and Model 3.

The concept of co-polymerization (instead of doping) was developed by Schmidt et al. (81), For instance, organometallic complexes of cobalt and rhodium were incorporated in Si02 by co-polymerization of tetraethoxy silane with tri-ethoxy silane complex ligands of these metals (82), Co-polymerizations were employed also in a recent Kodak patent (83) describing the preparation of dye-polymer/sol-gel composites. Copolymerizations aimed at achieving optical non-linearity were already mentioned in Section 41.2. Two additional examples are given in references 84,85,... 

Novel materials are thus needed to improve the mechanical and chemical stability of the sensor for practical applications in various conditions and, on the other hand, to improve the immobilization scheme in order to ensure sensor stability and the spatial control of biomolectdes. The most important materials for chemical and biochemical sensors include organic polymers, sol-gel systems, semiconductors and other various conducting composites. This chapter reviews the state-of-the-art biosensing materials and addresses the limitations of existing ones. 

Novel oiganic/inorganic hybrid materials known as ceramers have been developed in recent years by Wilkes and co-workers. Such materials are an example of a 3D nanocomposite, meaning a material where the degree of dispersion is of the order of nanometers compared to the more common microcomposite scale. Familiar microcomposites include emulsions, filled elastomers, protective coadngs equivalent nanocomposites are microemulsions, polymer/sol-gel inorganic composites, self-assembled monolayers (2D nanocomposites). 

Enzymes were immobilized using various conducting materials such as sol-gel composites with integrated graphite particles [195] however, there are still problems regarding a low sensitivity and undefined electron transfer. Moreover, in the case of the entrapment of enzymes into conducting-polymer films, possible direct electron transfer [150, 151] is stiU under discussion [196-198]. 

Novak B.M, Davies C. Inverse organic-inorganic composite materials. 2. Free-radical routes into nonshrinking sol-gel composites. Macromolecules 1991 24 5481-5483 Novak BM. Hybrid nanocomposite materials— between inorganic glasses and organic polymers. Adv. Mater. 1993 5(6) 422-33... 

Rouse, J.H. Polymer-assisted dispersion of single-walled carbon nanotubes in alcohols and applicability toward carbon nanotube/sol-gel composite formatiom7,a gwf r>.2005, 27(3), 1055-1061. 

Chibac, A.L., Melinte, V., Buruiana, T., et al. Preparation of photocrosslinked sol-gel composites based on urethane-acrylic matrix, silsesquioxane sequences, Ti02, and Ag/Au nanoparticles for use in photocatalytic apphcations. J. Polym. Sci. A Polym. Chem. 53, 1189-1204 (2015)... 

We reported previously that the mechanical properties of the amorphous etheric poly[bis(methoxyethoxyethoxy)-phosphazene] (MEEP) were significantly improved by in situ polymerization of tetraethoxysilane (TEOS) (4). This work on etheric phosphazene composites was consistent with reports from the research groups of Mark (5) and Wilkes (6), where metal alkoxides were added to poly(dimethylsiloxane) and poly(tetramethylene oxide). We now extend the phosphazene sol-gel composites to include the more reactive metal alkoxides of titanium, zirconium, and aluminum, and we report that when polymerized in situ, each is compatible with the etheric phosphazene polymer. Dynamic mechanical and stress-strain techniques are utilized to evaluate and compare the mechanical properties of the different composites. Thermal and... 

Figure 4. PVPh and partially condensed TEOS both have hydroxy functionality that promote miscibility in polym blends and control phase separation in sol-gel composites.

Recently, interesting composite materials incorporating polymeric materials into the sol-gel glasses have been reported by Wilkes and his co-workers [9]. These materials are named ceramers . The properties of ceramers strongly depend on the reaction conditions, i.e., acidity, water content, reaction temperature, the amount of organic polymer, the molecular weight of polymer, solvent, and so on. 

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