Colloid particles, stability

Fig. 4. Schematic of polymer colloidal particles stabilized by PFOA homopolymer [103]...

Radtchenko IL, Sukhorukov GB, Leporatti S, Khomutov GB, Donath E, Mohwald H. Assembly of alternated multivalent ion/polyelectrolyte layers on colloidal particles. Stability of the multilayers and encapsulation of macromolecules into polyelectrolyte capsules. Journal of Colloid Interface Science 2000, 230, 272-280. 

Colloidal particles may be attracted (lyophilic) or repelled (lyophobic) by their dispersion medium. (The dispersion medium in a colloid is analagous to the solvent in a solution.) Lyophobic colloids form when amphipathic or charged particles adsorb to the surface of tire colloidal particles stabilizing them in the dispersion medium. Protein in water is an example of a lyophilic colloid emulsyfied fat in water is an example of a lyophobic colloid. 

Armes and coworkers have investigated the structure of both PAn colloid particles [stabilized with poly(vinyl alcohol)] and electrochemically prepared PAn films. In both cases the fundamental morphology was nanoparticles of up to 20 nm in diameter. Colloid particles were rice grain shaped. Thick films showed submicronsized features that appear to be aggregates of the smaller particles. 

If, near to the CFPT, the configurational entropy of the particles contributes to the stability of colloidal particles stabilized by low molecular weight species, then it is reasonable to ask why this configurational entropy... 

Figure 10.11 (a) TEM image of PS colloidal particles stabilized by clay-PS and (b) a magnified... 

Figure 6-13. Transmission electron micrograph of 36 nm gold colloid particles stabilized with P(m-C6H4S03Na)3. The mean distance between colloid particle surfaces corresponds to two layers of the ligand. (Reproduced by permission from ref. [175].)...

The repulsion between two double layers is important in determining the stability of colloidal particles against coagulation and in setting the thickness of a soap film (see Section VI-5B). The situation for two planar surfaces, separated by a distance 2d, is illustrated in Fig. V-4, where two versus x curves are shown along with the actual potential. 

Among the many applications of LB films, the creation or arrangement of colloidal particles in these films is a unique one. On one hand, colloidal particles such as 10-nm silver sols stabilized by oleic acid can be spread at the air-water interface and LB deposited to create unique optical and electrooptical properties for devices [185]. 

Water and Waste Water Treatment. PAG products are used in water treatment for removal of suspended soHds (turbidity) and other contaminants such as natural organic matter from surface waters. Microorganisms and colloidal particles of silt and clay are stabilized by surface electrostatic charges preventing the particles from coalescing. Historically, alum (aluminum sulfate hydrate) was used to neutralize these charges by surface adsorption of Al cations formed upon hydrolysis of the alum. Since 1983 PAG has been sold as an alum replacement in the treatment of natural water for U.S. municipal and industrial use. 

FIG. 4 Sterically stabilized colloidal particles are coated with short polymer brushes. A hard sphere-like interaction arises. 

Based on the application of the established theory of colloid stability of water treatment particles [8,85-88], the colloidal particles in untreated water are attached to one another by van der waals forces and, therefore, always tend to aggregate unless kept apart by electrostatic repulsion forces arising from the presence of electrical charges on the particles. The aggregation process... 

Comprehension of the interactions among microstructures composed of tethered chains is central to the understanding of many of their important properties. Their ability to impart stability against flocculation to suspensions of colloidal particles [52, 124, 125] or to induce repulsions that lead to colloidal crystallization [126] are examples of practical properties arising from interactions among tethered chains many more are conceivable but not yet realized, such as effects on adhesion, entanglement or on the assembly of new block copolymer microstructures. We will be rather brief in our treatment of interactions between tethered chains since a comprehensive review has been published recently of direct force measurements on interacting layers of tethered chains [127]. 

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

PVP, a water soluble amine-based pol5mer, was found to be an optimum protective agent because the reduction of noble metal salts by polyols in the presence of other surfactants often resulted in non-homogenous colloidal dispersions. PVP was the first material to be used for generating silver and silver-palladium stabilized particles by the polyol method [231-233]. By reducing the precur-sor/PVP ratio, it is even possible to reduce the size of the metal particles to few nanometers. These colloidal particles are isolable but surface contaminations are easily recognized because samples washed with the solvent and dried in the air are subsquently not any more pyrophoric [231,234 236]. 

Bifunctional spacer molecules of different sizes have been used to construct nanoparticle networks formed via self-assembly of arrays of metal colloid particles prepared via reductive stabilization [88,309,310]. A combination of physical methods such as TEM, XAS, ASAXS, metastable impact electron spectroscopy (MIES), and ultraviolet photoelectron spectroscopy (UPS) has revealed that the particles are interlinked through rigid spacer molecules with proton-active functional groups to bind at the active aluminium-carbon sites in the metal-organic protecting shells [88]. 

The presence of shielding compounds interferes with subsequent processes, as the formation of metal-support interactions is able to stabilize supported particles. Moreover, the shielding effect of the colloid protectors prevents the contact of metal particles with the reacting molecules, thus avoiding the use of unsupported colloidal particles as a catalytic system [11]. 

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