Colloidal Silica Particles

Stabilizing effects have been directly observed by pulse radiolysis studies of silver cluster coalescence supported on 4-nm silica colloidal particles (44). Very small oligomeric clusters absorbing at 290 nm and 330 nm are stable in the presence of oxygen and even Cu " or Ru(NH3)6Cl3 (E° = 0.2 Vnhe)-These supported the exhibition of higher redox potentials than for free oligomeric clusters. 

Kim et al fabrieated SWNT composite films with ordered voids by using saerificial 2D siliea colloidal template (Figure 6.7). Experimentally, SWNTs stabilized with water-soluble polythiophene were mixed with a suspension of silica colloidal particles, and then assembled into 2D colloid-SWNT array on flexible substrate. Selective removal of silica colloids led to a composite film... 

T. Kito, N. Enomoto, H. Nishida, M. Komatsu, Modification of mono-dispersed silica colloid particles with polymer silane coupling agents, Polym. Adv. Technd. 1992, 3, 91-93 (b) K. Yoshinaga, K. Sueishi,... 

J. Lee, J. Won, J. Kim, K. Kim, S. Lee, Evaporation-induced, self-assembled, silica colloidal particle-assisted nanoporous structure evolution of poly (ethylene terephthalate) nonwoven composite separators for high-safety/high-rate lithium ion batteries, J Power Sour 216 (2012) 42-47. 

The success in fabrication of crackless bodies may be attributed to large sizes of silica particles and accordingly, large pores. It is explained that the added silica colloid particles grow to larger size particles as a result of reaction with Si(OC2H5)4 molecules in the solntion. 

Collimation Collimators (+)-CoUinusin S. collinus Tb 365 Colloidal particles Colloidal silica Colloidal silver Colloidal state Colloidal sulfur Colloid mills Colloids... 

Natural colloid particles in aqueous systems, such as clay particles, silica, etc. may serve as carriers of ionic species that are being sorbed on the particulates (pseudocolloids). It seems evident that the formation and transport properties of plutonium pseudocolloids can not yet be described in quantitative terms or be well predicted. This is an important area for further studies, since the pseudocolloidal transport might be the dominating plutonium migration mechanism in many environmental waters. 

A solid emulsion is a suspension of a liquid or solid phase in a solid. For example, opals are solid emulsions formed when partly hydrated silica fills the interstices between close-packed microspheres of silica aggregates. Gelatin desserts are a type of solid emulsion called a gel, which is soft but holds its shape. Photographic emulsions are gels that also contain solid colloidal particles of light-sensitive materials such as silver bromide. Many liquid crystalline arrays can be considered colloids. Cell membranes form a two-dimensional colloidal structure (Fig. 8.44). 

The first phase in the process is the formation of the sol . A sol is a colloidal suspension of solid particles in a liquid. Colloids are solid particles with diameters of 1-100 nm. After a certain period, the colloidal particles and condensed silica species link to form a gel - an interconnected, rigid network with pores of submicrometer dimensions and polymeric chains whose average length is greater than one micrometer. After the sol-gel transition, the solvent phase is removed from the interconnected pore network. If removed by conventional drying such as evaporation, so-called xerogels are obtained, if removed via supercritical evacuation, the product is an aerogel . 

The sorbents were hydrophobic Teflon, hydrophobic polystyrene (PS), and hydrophilic silica. These sorbents were negatively charged colloidal particles having smooth surfaces. In adition, PS particles at the surface of which oligomers (8-mers) of ethylene oxide ((EO)8) were grafted at a... 

The amounts oi adsorption of the polymer on latex and silica particles were measured as follows. Three milliliters of the polymer solution containing a known concentration was introduced into an adsorption tube(lO ml volume) which contained 2 ml of latex (C = l+.O wt %) and silica(C = 2.0 wt %) suspensions. After being rotated(l0 rpm) end-over-end for 1 hr in a water bath at a constant temperature, the colloid particles were separated from the solution by centrifugation(25000 G, 30 min.) under a controlled temperature. The polymer concentration that remained in the supernatant was measured colorimetrically, using sulfuric acid and phenol for the cellulose derivatives(12), and potassium iodide, iodine and boric acid for PVA(13). From these measurements, the number of milligrams of adsorbed polymer per square meter of the adsorbent surface was calculated using a calibration curve. 

Fig. 4.2 TEM images of fabricated nanoparticles, (a) Isolated composite core/shell submicron particles, (b) Hollow silica submicron particles prepared by removing the polystyrene core to demonstrate the high quality of the formed sol gel shell of the composite nanospheres employed to prepare sensing colloidal crystal films...

Colloidal particles, foams used to collect and separate, 12 22 Colloidal powders, 23 55-56 Colloidal silica, 22 380, 382, 384 applications of, 22 394 modification of, 22 393-394 preparation of, 22 392-393 properties of, 22 391-392 purification of, 22 393 Colloidal silica gels, 23 60 Colloidal solids, 7 293-294 Colloidal stability, 7 286-291 10 116 22 55 Colloidal stabilizers, in polychloroprene latex compounding, 19 857 Colloid mills, 8 702 10 127 Colloids, 7 271-303 23 54. See also Polymer colloids analysis, 7 296 applications, 7 292-296 conducting, 7 524... 

A scaled-up version of this central template-concentric sphere surface assembly approach has been demonstrated for the growth of multi-layer core-shell nano- and microparticles, based upon the repeated layer-by-layer deposition of linear polymers and silica nanoparticles onto a colloidal particle template (Figure 6.8) [60]. In this case, the regioselective chemistry occurs via electrostatic interactions, as opposed to the covalent bond formation of most of the examples in this chapter. The central colloidal seed particle dictates the final particle... 

If a surface precipitate of metal hydroxy-polymer has formed on an adsorbent, the -pH relationship for the coated adsorbent should resemble closely that observed for particles consisting purely of the hydroxy-polymer or the hydrous oxide of the metal (15). This kind of evidence for Co(ll), La(lII), and Th(lV) precipitation on silica colloids was cited by James and Healy (15). It should be noted, however, that the increase in C toward a maximum value often occurs at pH values well below that required thermodynamically to induce bulk-solution homogeneous precipitation of a metal hydrous oxide (15, 16). If surface precipitation is in the incipient stage under these conditions, it must be a nucleation phenomenon. James and Healy (15) argue that the microscopic electric field at the surface of a charged adsorbent is sufficiently strong to lower the vicinal water activity and induce precipitation at pH values below that required for bulk-solution precipitation of a metal hydrous oxide. 

In Zerrouki s experiments, the preparation of aqueous phases of identical clusters is performed in six steps. First, colloidal particles of silica, 1.2 pm in diameter, are synthesized. Next, the surface of the particles is made hydrophobic by chemical grafting. Then, an oil-in-water premix emulsion is made by adding an octane suspension of the colloids in an aqueous solution. Controlled shear of the premix in a Couette-type apparatus is subsequently performed to obtain a quasi-monodisperse... 

Colloidal silica films spin-coated onto a glass substrate constitute another method to increase the surface area and therefore number of capture sequences which can be available for hybridization [43]. In this context, 0.3 p,m layers have been deposited from 20 wt % colloidal silica suspensions (particle size 16 to 65 nm). Heating to 350 °C for four hours is required to render the films sfable (fhrough parfial sinfering of fhe film with the underlying substrate). The particles pack randomly with no noticeable short- or long-range order. 

In colloidal systems, van der Waals forces play a prominent role. When any two particles (neutral or with charges) come very close to each other, the van der Waals forces will be strongly dependent on the surrounding medium. In a vacuum, two identical particles will always exhibit an attractive force. On the other hand, if two different particles are present in a medium (in water), then there may be repulsion forces. This can be due to one particle adsorbing with the medium more strongly than with the other particle. One example will be silica particles in water medium and plastics (as in wastewater treatment). It is critical to understand under what conditions it is possible that colloidal particles remain suspended. For example, if paint aggregates in the container, then it is obviously useless for its intended purpose. 

Oh, S.J. Cook, D.C. Townsend, H.E. (1998) Characterization of iron oxides commonly formed as corrosion products on steel. Hyper-fine Interactions 112 59-65 Ohmori, M. Matijevic, E. (1992) Preparation and properties of uniform coated inorganic colloidal particles. VII. Silica on hematite. J. Colloid Interface Sci. 150 594-598 Ohta, S. Effendi, S. Tanaka, N. Miura S. (1993) Ultisols of lowland Dipterocarp forest in East Kalimantan, Indonesia. Soil Sci. Plant Nutr. 39 1-12... 

---