Silica colloids

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

We have shown a new concept for selective chemical sensing based on composite core/shell polymer/silica colloidal crystal films. The vapor response selectivity is provided via the multivariate spectral analysis of the fundamental diffraction peak from the colloidal crystal film. Of course, as with any other analytical device, care should be taken not to irreversibly poison this sensor. For example, a prolonged exposure to high concentrations of nonpolar vapors will likely to irreversibly destroy the composite colloidal crystal film. Nevertheless, sensor materials based on the colloidal crystal films promise to have an improved long-term stability over the sensor materials based on organic colorimetric reagents incorporated into polymer films due to the elimination of photobleaching effects. In the experiments... 

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. 

NaLS promotes the reaction as both Ru and MV++ are bound, and the product Ru is maintained at the micelle while MV+ regresses to the aqueous phase (12 -15). The use of a Ru1 derivative with a long hydrocarbon chain also assists the reaction. If a negatively charged silica colloid is used in place... 

It should be realized, at the outset, that colloidal solutions (unlike true solutions) will almost always be in a metastable state. That is, an electrostatic repulsion prevents the particles from combining into their most thermodynamically stable state, of aggregation into the macroscopic form, from which the colloidal dispersion was (artificially) created in the first place. On drying, colloidal particles will often remain separated by these repulsive forces, as illustrated by Figure 1.1, which shows a scanning electron microscope picture of mono-disperse silica colloids. 

Figure 1.1 Scanning electron microscope image of dried, mono-disperse silica colloids.

Perikinetic Coagulation. The concentration of small silica colloids (Ludox LS d = 15 m/ ) used in these studies was between 0.18 gram/liter and 0.43 gram/liter (36.5 — 86.0 meter2/liter or 5.0-11.5 X 1013 par-ticles/ml.). The dispersion, contained in a spectrophometric cell, was... 

Silicas - [COLLOIDS] (Vol6) -m automobile polishes [POLISHES] (Vol 19) -m friction materials [BRAKE LININGS AND CLUTCH FACINGS] (Vol 4) -m pharmaceuticals [PHARMACEUTICALS] (Vol 18)... 

Light-scattering experiments on flocculating suspensions of silica colloids provided the data in the following table. (R is the average cluster radius.) Estimate the fractal dimension of the clusters formed and indicate whether the flocculation process is transport or reaction controlled. Hint Apply Eq. 6.1 and the concepts in Section 6.1.)... 

The hydration force is important for distances between plates less than a few nanometers. Since the DLVO potential barrier between spherical particles or droplets is located at separation distances of the order of the Debye length, it is clear that at least at high electrolyte concentrations the hydration force becomes relevant. The qualitative effect of hydration was earlier recognized, regarding the stability of silica colloids at high electrolyte concentrations1 or the stability of amphoteric latex particles at high concentrations of some electrolytes.12... 

Solberg D, Wagberg L (2003) Adsorption and flocculation behaviour of cationic polyacrylamide and colloidal silica. Colloids Surf A Physicochem Eng Aspects 219 161... 

In some cases, it may be necessary to take into account more specific interactions, such as hydration forces in the example of silica colloids. 

In addition to recent advances in block co-polymer templating of periodic mesoporous silica and silica colloidal crystal templating of periodic mesopo-rous polymers [79], SAMs have been used for polymer patterning [80]. Mixtures of two strongly incompatible polymers, a polystyrene (PS)-polyvinylpyridine (PVP) blend, were found to phase separate when placed on a... 

The three most common abrasives for oxide CMP slurries are fumed silica, colloidal silica, and ceria. The advantage of fumed silica is that the purity of the... 

Structure of silica colloids. Present ideas on the state of silica in aqueous solutions are examined in detail in the review by Sretenskaya (1970), where it is mentioned that one of the most typical features is the tendency to polymerize, i.e. to convert from a molecularly dispersed to a colloidally dispersed state. Polymerization is based on the process of condensation of silicol groups Si(OH)4 with liberation of water and as a result formation of the siloxane bonds Si-O-Si. 

Stability of mixed iron-silica colloidal solutions... 

In an experimental study of mixed iron-silica colloids we found the opposite phenomenon, stabilization of colloids of iron hydroxide by silica colloids, which is manifested very clearly in undialyzed iron hydroxide sols of average concentration with a ratio of Fe203 SiOj = 1 3. Colloidal iron in mixed solutions proved to be more resistant to the action of electrolytes than in isolated sols of iron hydroxide. Only colloidal silica shows any stabilizing effect on sols of iron hydroxide dilute solutions undersaturated with Si(OH)4 are not stabilizers. It is characteristic that colloidal silica is capable of stabilizing colloidal iron in the same pH ranges in which pure silica sols are stable in acid (pH < 4) and alkaline (pH > 8) environments. In slightly acid environments (pH = 5-6) iron-silica sols are unstable and decompose to form mixed sediments, which sometimes are not uniform due to different rates of coagulation and deposition. 

Quaternary ammonium compound Quaternary base Quaternary compound Quaternary compound Quaternary fatty acid derivative Quaternary fatty derivatives Quaternized condensation polymer Silica, colloidal Silica, colloidal Silica, colloidal Silica, modified Silica blend, reacted Silicate Silicic acid Silicone Silicone... 

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