Silica/polymer composites

Toth B, Laszlo K, Horvai G (2005) Chromatographic behavior of silica-polymer composite molecularly imprinted materials. J Chromatogr A 1100(l) 60-67... 

J.-P. Boisvert, J. Persello, and A. Guyard, Influence of the surface chemistry on the structural and mechanical properties of silica-polymer composites, J. Polym. Sci. Part B Polym. Phys., 41, 3127-3138 (2003). 

Usually the silica/polymer composites are prepared with styrene, MMA, BA, or their copolymers. However, few reports cover experiments with less commonly used polymers such as poly(styrene sulfonic acid) (PSSA), poly(hydroxyethylmethacry-late) (PHFMA), poly(aminoethylmethacrylate) PAEMA [133], polyethylene (PE) [134], or polyamides [135]. Using a miniemulsion of nickel-based catalysts for the polymerization of ethylene, which is dispersed in toluene in the presence of hy-drophobically modified silica particles, PEysilica hybrids could be prepared [134]. The ethylene is introduced into the system by bubbling through the miniemulsion. The hydrophobic moiety of the silica particles interacts with the growing polymer and leads to lentil-shaped or isotropic hybrids. Lentil-shaped particles are composed of semicrystalline PE, whereas the isotropic hybrids are composed of amorphous polymer. The crystallinity of the polymer is determined by the choice of polymerization catalyst. Silica/polyamide hybrid nanoparticles were prepared with 3-aminopropyltriethoxysilane (APS)-modified silica particles [135]. These particles were dispersed in sebacoylchloride and the solution miniemulsifled in an aqueous... 

Leventis, N, Palczer A, McCorkle L, Zhang G, Sotiriou-Leventis C (2005) Nanoengineered silica-polymer composite aerogels with no need for supercritical fluid drying. J Sol-Gel Sci Tech 35 99-105. 

In addition to HA, silica has been used to improve PCL mechanical properties without compromising biocompatibility (CalandreUi et al., 2010). In this study, PCL and silica surfaces were modified to chanicaUy bond to each other, which reflects the criterion that nanocomposites should have a strong combination between components. Another study (Wei et al., 2009) observed the formation of apatite and the promoted cell proliferation on a calcium-silica-reinforced PCL, which further justifies the use of silica-polymer composite for bone-tissue engineering. 

FIGURE 3.8 Scanning electron microscopic (SEM) pictures of acrylic mbber (ACM)-silica hybrid composites (a) synthesized from 50 wt% tetraethoxysilane (TEOS) and (b) synthesized from 10 parts of precipitated silica. (From Bandyopadhyay, A., Bhowmick, A.K., and De Sarkar, M., J. Appl Polym. Sci., 93, 2579, 2004. Courtesy of Wiley InterScience.)... 

FIGURE 3.12 Morphology of mbber-silica hybrid composites synthesized from solution process using different solvents (a) and (b) are the scanning electron microscopic (SEM) pictures of acrylic rubber (ACM)-silica hybrid composites prepared from THF (T) and ethyl acetate (EAc) (E) and (c) and (d) are the transmission electron microscopic (TEM) pictures of epoxidized natural rubber (ENR)-siUca hybrid composites synthesized from THF and chloroform (CH). (From Bandyopadhyay, A., De Sarkar, M., and Bhowmick, A.K., J. Appl. Polym. Sci., 95, 1418, 2005 and Bandyopadhyay, A., De Sarkar, M., and Bhowmick, A.K., J. Mater. Sci., 40, 53, 2005. Courtesy of Wiley InterScience and Springer, respectively.)... 

Various finishes can be achieved — gloss, satin (or egg-shell) or matt. This is accomplished by the addition of particles of size 1-5 pm of, for example, silica, china clay or the white pigment, TiCK The degree of mattness depends on various factors, such as particle size, surface treatment of the particles, rate of film formation, and the polymer composition, e.g., urethane/acrylate compared with epoxy/acrylate. The former requires smaller particles larger particles cannot be used as they create a rough surface. 

In the X-ray powder diffraction patterns of the composites, the disappearance of the broad band centered at 22 °20, typical of amorphous silica, indicates that the zeolitisation of the mineral fraction of the parent composite was complete. In no diffraction pattern any sign of crystallised chitosan could be found. The two methods in which the silica-polymer beads were extracted from the aluminate solution after impregnation (methods A and C) allowed the formation of the expected zeolite X, with traces of gismondine in the case of the method C. The method B, in which excess aluminate solution was present during the hydrothermal treatment, resulted in the formation of zeolite A. 

The silica microspheres provide some diversity but not enough for many complex discrimination tasks. To introduce more sensor variety, hollow polymeric microspheres have been fabricated8. The preparation of these hollow microspheres involves coating silica microspheres by living radical polymerization, using the surface as the initiation site. Once the polymer layer forms on the silica microbead surface, the silica core is removed by chemical etching. These hollow spheres can be derivatized with the dye of interest. The main advantage of these polymer microspheres is the variety of monomers that can be employed in their fabrication to produce sensors with many different surface functionalities and polymer compositions. 

It was apparent that the dense adsorption layer of HPC which was formed on the silica particles at the LCST plays a part in the preparation of new composite polymer latices, i.e. polystyrene latices with silica particles in the core. Figures 10 and 11 show the electron micrographs of the final silica-polystyrene composite which resulted from seeded emulsion polymerization using as seed bare silica particles, and HPC-coated silica particles,respectively. As may be seen from Fig.10, when the bare particles of silica were used in the seeded emulsion polymerization, there was no tendency for encapsulation of silica particles, and indeed new polymer particles were formed in the aqueous phase. On the other hand, encapsulation of the seed particles proceeded preferentially when the HPC-coated silica particles were used as the seed and fairly monodisperse composite latices including silica particles were generated. This indicated that the dense adsorption layer of HPC formed at the LCST plays a role as a binder between the silica surface and the styrene molecules. 

The precipitated silica (J. Crosfield Sons) was heated in vacuo at 120° for 24h. before use. Two grades of surface areas 186 and 227 m g l (BET,N2), were used during this project. Random copolymers, poly(methyl methacrylates) and polystyrene PS I were prepared by radical polymerization block polymers and the other polystyrenes were made by anionic polymerization with either sodium naphthalene or sodium a methylstyrene tetramer as initiator. The polymer compositions and molecular weights are given in Table I. 

Finally the synthesis of inorganic-polymer composite membranes should be mentioned. Several attempts have been made to combine the high permeability of inorganic membranes with the good selectivity of polymer membranes. Furneaux and Davidson (1987) coated a anodized alumina with polymer films. The permeability increased by a factor of 100, as compared to that in the polymer fiber, but the selectivities were low (H2/O2 = 4). Ansorge (1985) made a supported polymer film and coated this film with a thin silica layer. Surprisingly, the silica layer was found to be selective for the separation mixture He-CH4 with a separation factor of 5 towards CH4. The function of the polymer film is only to increase the permeability. No further data are given. 

A large number of inorganic and organic substances are used as fillers in polymer composites. Calcium carbonate, barium sulfate, clays, silica, and talc are common examples. Glass beads are often used in traffic paints to increase reflectivity. Metal fibers are sometimes added to impart conductivity or to improve metal plating. A number of organic materials are also used, including wood flout cellulose, and even corncobs. We will encounter starch/ ... 

Xu, T., Cheng, Z., Zhang, Q. et al.. Fabrication and characterization of three-dimensional periodic ferroelectric polymer-silica opal composites and inverse opals, J. Appl. Phys., 88, 405, 2000. 

Highly ordered hexagonal mesoporous carbon nitride material[267] can be synthesized by the following procedure. Calcined SBA-15 is added to a mixture of ethylenediamine and carbon tetrachloride. The resultant mixture is refluxed at 90 °C for 6 h. The template carbon nitride polymer composite is then heat-treated in a nitrogen flow at 600 °C. The mesoporous carbon nitride is recovered after dissolution of the silica framework in HF solution. 

Figure 14.16. The effect of mean particle size of silica on total acoustic emission of epoxy filled with 70% silica. [Data from Ohta M, Nakamura Y, Hamada H, Maekawa Z, Polym. Polym. Composites, 2, No.4, 1994, 215-21.]...

In a general way, the larger the amount of SiO2 and total acid constituents, the larger the size of hypothetical average silica polymer species in the melt. Gaskell has described a relationship between silica species and the basic composition ( ). 

---