Silica microsphere

The third line of development was to increase the selectivity in order to achieve the highest possible resolution to address difficult separations. This may be achieved by a very narrow pore size distribution of the media, e.g., such as achieved by porous silica microspheres (PSM) or by modifying the porous phase by a composite material, e.g., as for Superdex. In practice, this material shows a maximum selectivity over the separation range (e.g., see Fig. 2.2). 

ZORBAX POROUS SILICA MICROSPHERE COLUMNS FOR HIGH-PERFORMANCE SIZE EXCLUSION CHROMATOGRAPHY... 

In 1972, Kirkland at E. I. du Pont de Nemours patented porous silica microspheres (PSM) specifically for high-performance liquid chromatography (HPLC) applications (3). Prior to this development, silica particles used for chromatographic applications were simply adapted from some other use. In the 1970s, Kirkland showed that porous silica particles could be used for size-... 

FIGURE 3.1 Formation of Zorbax porous silica microspheres. 

Kirkland J.J., Dilks, Jr., C.H., and DeStefano J. J., Normal-phase high-performance liquid chromatography with highly purified porous silica microspheres, /. Chromatogr, 635, 19, 1993. 

Kirkland, J. J. and Antle, P. E., High-performance size-exclusion chromatography of small molecules with columns of porous silica microspheres, J. Chromatogr. Sci., 15,137,1977. 

Dhas NA, Zaban A, Gedanken A (1999) Surface synthesis of zinc sulfide nanoparticles on silica microspheres sonochemical preparation, characterization, and optical properties. Chem Mater 11(3) 806-813... 

Ramesh S, Yuri K, Ruslan P, Aharon G (1997) Sonochemical deposition and characterisation of nanophasic amorphous nickel on silica microspheres. Chem Mater 9 546-551... 

Thermal analysis techniques reveal that water is bound in opal in more than one manner. Most of the water is physically held in inclusions or microscopic pores within the opal, that is, in spaces between the microspheres. Water held in this manner can escape through complex systems of microscopic fissures or cracks, induced by temperatures even below 100°C. Some water is held within the opal via chemical bonding ( adsorption ) to the surfaces of the silica microspheres and is retained to temperatures approaching 1000°CJ7J Furthermore, since the microspheres themselves are composed of much smaller silica particles, water is additionally coated on the surfaces of these minute particles. The porous nature of opal and its thermal sensitivity require special care, for dehydration may result in cracking that greatly diminishes the value of this gemstone. 

Fowler, C.E., Khushalani, D. and Mann, S. (2001) Facile synthesis of hollow silica microspheres. Journal of Materials Chemistry, 11, 1968—1971. 

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. 

An important demonstrated application of this artificial nose system is the high-speed detection of low levels of explosives and explosive-like vapors. Several sensors, based on Nile Red attached to silica microspheres, show high sensitivity to nitroaromatic compounds (NAC) within a mixture12. Different fluorescence response profiles were observed for several NAC s, such as 1,3,5-trinitrotoluene (TNT) and 1,3-dinitrobenzene (DNB), despite their similar structures. These responses were monitored at low concentrations of the NAC vapors (ca. 5 ppb) and at short vapor exposure... 

Cai, M. Painter, O. Vahala, K. J., Observation of critical coupling in a fiber taper to a silica microsphere whispering gallery mode system, Phys. Rev. Lett. 2000, 85, 74 77... 

Collot, L. Lefevre Seguin, V. Brune, M. Raimond, J. M. Haroche, S., Very high Q whis pering gallery mode resonances observed on fused silica microspheres, Europhys. Lett. 1993, 23, ill 334... 

Rezac, J. P., Properties and Applications of Whispering Gallery Mode Resonances in Fused Silica Microspheres, PhD dissertation, Oklahoma State University, 2002... 

The microspheres—synthesised via a two-step process (acid-catalysed hydrolysis and condensation of 3-mercaptopropyltrimethoxysilane (MPS) in aqueous solution, followed by condensation catalysed by triethanolamine)—have a narrow size distribution (Figure 5.16) and are considerably more stable than polystyrene divinylbenzene microspheres as shown in phosphoramidite oligonucleotide synthesis by the excellent retention of fluorescence intensity in each of the reagent steps involved in phosphoramidite DNA synthesis (Figure 5.17, in which the organo-silica microsphere free thiol groups are derivatized with ATTO 550 maleimide coupled to the entrapped dye). 

T Yamasaki, K Sumioka, and T Tsutsui, Organic light-emitting device with an ordered monolayer of silica microspheres as a scattering medium, Appl. Phys. Lett., 76 1243-1245, 2000. 

Figure 1. Near-field intensity portraits (16.6% contours) of the high-Q WGio,i modes supported by a silica microsphere (a) and a GaAs microdisk (b).

Lefevre-Seguin, V., and Haroche, S., 1997, Towards cavity-QED experiments with silica microspheres, Maier. Sci. Eng. B 48 53-58. 

FIGURE 6.5 The measured power of the third harmonic power generated in the bulk of solution containing 0.5- xm-diameter fused silica microspheres as a function of microspheres concentration. Circles are experimentally measured data points the dashed line is a linear fit. 

A polymer called latex, prepared from a monomer that contains organic groups, is deposited as small spheres (0.1—0.3 pm in diameter) on the support to form a continuous film about 1—2 pm thick. The support is made of silica microspheres or spheres of polystyrene of about 25-50 pm diameter (Fig. 4.4). 

Syntactic foams manufactured from hollow glass or silica microspheres and an epoxide, phenolic or other matrix resin represent a class of lightweight structural materials used for buoyancy purposes, insulation and packaging. The effect of silanes on the mechanical properties of syntactic foams at a nominal density of 0.35 g/cm3 is shown in Tables 14-16. The Proportional Limit is defined as the greatest stress which the foam is capable of sustaining without any deviation from proportionality of stress to strain (Hooke s Law). 

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