Adsorbent colloidal silicas

Particles of colloidal silicates of polyvalent metals, for example, clay and asbestos, adsorb colloidal silica. Addition of colloidal silica improves dispersion and lowers viscosity of dispersions of asbestos in water without Introducing strong alkali such as sodium silicate (688, 689). 

Lower and coworkers [199] have investigated the adsorption of T4 lysozyme on colloidal silica. It was observed that the enzymatic activity decreased upon adsorption due to the differences in adsorbed enzyme structure and orientation as well as the electrostatic effects. 

Based on this approach Schouten et al. [254] attached a silane-functionalized styrene derivative (4-trichlorosilylstyrene) on colloidal silica as well as on flat glass substrates and silicon wafers and added a five-fold excess BuLi to create the active surface sites for LASIP in toluene as the solvent. With THF as the reaction medium, the BuLi was found to react not only with the vinyl groups of the styrene derivative but also with the siloxane groups of the substrate. It was found that even under optimized reaction conditions, LASIP from silica and especially from flat surfaces could not be performed in a reproducible manner. Free silanol groups at the surface as well as the ever-present impurities adsorbed on silica, impaired the anionic polymerization. However, living anionic polymerization behavior was found and the polymer load increased linearly with the polymerization time. Polystyrene homopolymer brushes as well as block copolymers of poly(styrene-f)lock-MMA) and poly(styrene-block-isoprene) could be prepared. 

The accompanying data give the volume of N2 at STP adsorbed on colloidal silica at the temperature of liquid nitrogen as a function of the ratio p/p0. Plot these results according to the linear form of the BET equation. Evaluate c, Vm, and Asp from these results, using 16.2 A2 as the value for o°. 

Polymer beads have also been tagged by treating them after each new diversity-introducing reaction with dye-containing, colloidal silica particles, which can be irreversibly adsorbed on the surface of the beads with the aid of polyelectrolytes such as poly(diallyldimethylammonium chloride) and poly(acrylic acid) [42,43]. Larger portions of support can also be linked to a chip that enables electronic tagging with a radio emitter [44-46]. 

V. M. Gun ko, J. Skubiszewska-Zieba, R. Leboda, and V. V. Turov, Impact of Thermal and Hydrothermal Treatments on Structural Characteristics of Silica Gel Si-40 and Carbon/Silica Gel Adsorbents, Colloids Surf. A 235 (2004) 101-111. 

Silicon Dioxide occurs as an amorphous substance that shows a noncrystalline pattern when examined by X-ray diffraction. It is produced synthetically, either by a vapor-phase hydrolysis process, yielding fumed silica, or by a wet process, yielding precipitated silica, silica gel, colloidal silica, or hydrous silica. Fumed silica is produced in an essentially anhydrous state, whereas the wet-process products are obtained as hydrates or contain surface-adsorbed water. 

Besides process development and dissolution rate enhancement, the phenomenon of adsorption at solid surfaces is also useful in many other aspects of pharmaceutics. By adsorbing moisture onto its large surface area, colloidal silica has been frequently used as a... 

Although the detailed nature of the surface of costal strips is not known, evidence from binding studies indicate that cations such as Co and Fe + are preferentially adsorbed onto these structures (9). Similar interactions have been shown with organic and colloidal materials (9). For example, phospholipid vesicles were shown to be closely attached to the surfaces of costal rods incubated in aqueous dispersions of phosphatidylcholine for 24 hr. Similar observations were made for costal rods incubated in solutions of colloidal silica. These results indicate that a range of interactions can take place on the surface of biogenic silica and such events may serve important functional roles, such as inhibition of dissolution and adhesion of components in the construction of microscopic structures. 

Martini, G., The state of water adsorbed on silica gel as determined by ESR of transition metal ion probe, J. Colloid Interf. Sci., 80, 39, 1981. 

In a recent study, the necessity for understanding the effects that molecular probes (e.g., pyrene) can have on colloidal system has been clearly illustrated. " Mixtures of pyrene-labeled and unlabeled polyethylene oxide (PEO) were adsorbed on silica and the properties of the resulting suspension were monitored. Settling rate results (Eigure 7.29) clearly demonstrated that pyrene-labeled PEO has a marked effect on the flocculation of silica suspension. It has been shown that even relatively small amounts of labeled polymer, when mixed with unlabeled polymer, can dramatically affect the behavior of their mixtures. On the other hand, it has also been shown that when labeled polymer was used in sufficiently low amounts (<3%), the mixture behavior does not differ from that due to the unlabeled polymer. These findings once again underscore the fact that while certain measurement techniques are invaluable for investigating colloidal phenomena, potential effects caused by introduction of various molecular probes into the system should always be noted. 

Microelectrophoresis. A Zeta-Meter (Zeta Meter Inc.) was used in conjunction with a Plexiglas cell. Microelectrophoresis was conducted at 1 mM NaCl unless otherwise stated. Constant ionic strength was maintained as the pH was varied using 1 mM NaOH and 1 mM HC1 solutions. The polyions were adsorbed onto Minusil (colloidal silica), of particle size 2.7 ym (geometric weight-mean diameter, with a geometric standard deviation of 0.72 ym) prior to microelectrophoresis. A 0.02% w/v polyion solution and a 0.01 % w/v Minusil suspension were used. The electrophoretic mobility was the mean of at least 20 readings and the coefficient of variation was less than 5%. 

The origin of the coagulation behavior of Iler s silica sols is far from understood. The electrosteric barrier model herein proposed is designed to stimulate new experimental initiatives in the study of colloidal silica sol particles and their surface structure. The adsorbed steric layer, impregnated with bound (exchanged) cations, at the surface of 1-100-nm-diameter silica sol particles has the general properties needed to understand the anomalous coagulation behavior. The details await experimental and theoretical input. 

Frolov, Shabanova, and co-workers (37-39) studied the transition of a sol into a gel and the aggregate stability of colloidal silica. Their aim was to develop a technology for the production of highly-concentrated silica sols and to use them as binders, catalyst supports, polymer fillers, adsorbents, and so forth. Kinetic studies were made of polycondensation and gel formation in aqueous solutions of silicic acids. At the stage of particle growth, poly condensation proceeds in the diffusion-kinetic region. With changes in pH, temperature, concentration, and the nature of electrolytes,... 

Colloidal Alumina Alumina is available in a colloidal form which can be deposited on firebrick or glass beads, or on the wall of an open tubular column, to give a porous adsorptive layer which may be modified by addition of a liquid or other adsorbent such as colloidal silica. This way a wide variety of selective separating layers can be prepared. 

Natural surface ectivity In assoc ialion with surface-active agents Foam fractionation for example, dete[gents from aqueous solutions Ion flotation, molecular flotation, adsorbing colloid flotation for example, Sr1 +, PtiJ +, Hg2+, cyanides Fnam flotation for example, microurganisms, proteins Microflotation, colloid flotation, ultraflotation for example, particulates in wastewater, clay, microoiganisms Froth flotation of noapolar minerals for example, sulfur Froth flotation For example minerals such as silica Precipitate flotation (1st and 2nd kind) Tor example, ferric hydroxide... 

With the increased level of understanding of the cyclization dynamics as monitored by intramolecular excimer fluorescence, it is now possible to extend this probe to the study of systems more complex than dilute solutions. One such situation involves the structure and dynamics of macromolecular complexes formed between polymeric proton donors and acceptors in aqueous solution. For example, there has been widespread interest in the complexes formed between poly(ethylene glycol) and poly(acrylic acid) or poly(methacrylic acid) in aqueous solution (34, 35). A second, complicated morphological problem is to describe the configurational behavior of polymer chains adsorbed on colloidal particles. This research has relevance to the understanding of steric stabilization. One system of particular interest is the interaction of poly(ethylene glycol) and colloidal silica (36-40). 

Upon adsorption onto colloidal silica, the monomer excitation spectrum remained essentially unchanged from that of the solution. In this system, the excimer persisted, allowing study of its excitation spectrum. In this experiment, a substantial shift in the excimer excitation spectrum occurs, indicating that, although excimer-forming sites remain, they exist in a strained state. This observation is further supported by the time dependence of the excimer fluorescence decay. Whereas chains remain adsorbed on the colloidal silica surface, the excimers formed are substantially shorter lived than those in free solution. 

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