Encapsulation colloid stability

A number of refinements and applications are in the literature. Corrections may be made for discreteness of charge [36] or the excluded volume of the hydrated ions [19, 37]. The effects of surface roughness on the electrical double layer have been treated by several groups [38-41] by means of perturbative expansions and numerical analysis. Several geometries have been treated, including two eccentric spheres such as found in encapsulated proteins or drugs [42], and biconcave disks with elastic membranes to model red blood cells [43]. The double-layer repulsion between two spheres has been a topic of much attention due to its importance in colloidal stability. A new numeri-... 

Adsorption behavior and the effect on colloid stability of water soluble polymers with a lower critical solution temperature(LCST) have been studied using polystyrene latices plus hydroxy propyl cellulose(HPC). Saturated adsorption(As) of HPC depended significantly on the adsorption temperature and the As obtained at the LCST was 1.5 times as large as the value at room temperature. The high As value obtained at the LCST remained for a long time at room temperature, and the dense adsorption layer formed on the latex particles showed strong protective action against salt and temperature. Furthermore, the dense adsorption layer of HPC on silica particles was very effective in the encapsulation process with polystyrene via emulsion polymerization in which the HPC-coated silica particles were used as seed. 

Figure 9 Activity and enantioselectivity of the alginate encapsulated Pt-colloid stabilized by DH-CIN used repeatedly in the enantioselective hydrogenation of ethyl pyruvate in cyclohexane without adding fresh modifier before each hydrogenation cycle. 

Additionally, we have reviewed the current research on colloidal dispersions in terms of two thin-film systems generated from surfactant solutions. The aqueous phase surfactant forms a bilayer that encapsulates and stabilizes the solvent droplets. These novel gas-liquid and liquid-liquid macroemulsions appear to have high potential in technology and in interfacial catalysis. 

Similar work has been done by Gu et al. [154] on improving on the colloidal stability of the magnetic latex produced. Sodium p-styrene sulfonate (NaSS) was added in the course of the polymerization reaction. Very recently, silica-coated magnetic silica particles were encapsulated by a fluorescent polymeric shell of styrene and... 

Phosphazene substituted with glycine has been prepared as a passivation agent for CdSe (green emission) and CdSe/ZnS (red emission) quantum dots. The polymer was prepared by the reaction of ethylglycinate with poly(di-chlorophosphazene), which was then de-esterified by base to reveal the active material. Quantum dots were prepared for passivation by initial treatment with mercaptoethanol, followed by treatment with the phosphazene. Fluorescent CdSe/ZnS quantum dots were found to be encapsulated in the polymer, which acted as a multidentate pendant group. It was found to passivate the dots and provided colloidal stability. Encapulated ZnS exhibited fluorescence stability. 

Uses Emulsifier, thickener, colloidal stabilizer, binder for foods binder, diluent, absorbenL and disintegrant in pharmaceutical tablets food pkg. emulsifrer and encapsulant for oils in dry food mixes film-former opacifier, bodying agent in nonaq. cosmetic creams Re latrxy FDA 21 CFR 155.130,169.150,169.179,172.892,175.105, 178.3520,182.90... 

Well-defined particles have been obtained from PDMS containing different additives, using the surfactant depicted in Scheme 9. For example, metal nanoparticles, or crystalline compounds may be encapsulated in PDMS and the resulting particles are better defined and stable after drying (Figure 3), probably due to a reinforcing effect. The same result was observed in the case of PCL nanoparticles with encapsulated indomethacine. In that case, the colloidal stability was visibly increased compared to the neat polymer [92],... 

Cationic polymer-based nanogels are nanosized swollen cationic hydrogel particles composed of chemically or physically crosslinked polymer net-works/ The highly hydrated properties and tightly crosslinked core makes these systems superior in colloidal stability. These properties make these nanogels suitable for encapsulation of therapeutic nucleic acids in the core for carrier systems for delivery, in comparison to macroscopic hydrogels or nanoparticles. ... 

Properties Wh. powd., odorless, tasteless insol. in water, alcohol, ether, chloroform Hazardous Decomp. Prods. Heated to decomp., emits acrid smoke and irritating fumes Uses Emulsifier, thickener, colloidal stabilizer, binder for foods binder, diluent, absorbent, and disintegrant in pharmaceutical tablets food pkg. emulsifier and encapsulant for oils in dry food mixes film-former opacifier, bodying agent in nonaq. cosmetic creams Regulatory FDA 21CFR 155.130, 169.150, 169.179, 172.892, 175.105, 178.3520, 182.90 Manuf./Distrib. A.E. Staley Mfg. http //www.tateandlyle.com, ADM http //www.admworld.com, Ashland http //www.ashchem.com, Avebe BV Cerestar Int l. 

In this specific case, the colloid stabilizers are dendrimers, for instance, polyamidoamine (PAMAM), which are hyperbranched polymers that ramify from a single core and form a porous sphere [103, 104] (Scheme 17.1). Dendrimer-encapsulated nanoparticles (DENs) are synthesized by sequestering metal ions within appropriate dendrimers, and then by chemically reducing the resulting composite. They can be synthesized in various media, such as water or ethanol. The size of the nanoparticles is usually nearly monodisperse, and can be tuned by varying the metal-to-dendrimer ratio prior to reduction. Supported catalysts can then he prepared by immobilizing DENs onto a sohd support. As in the case of colloids, the last step, which consists in the removal of dendrimers hy thermal treatment, may lead to an increase in both the metal-particle size and particle-size distribution. 

Seeded emulsion polymerization is a widely accepted technique for the encapsulation of inorganic particles (see Chapter 4). Polymerization onto the particle surface is favored over the formation of new particles in the bulk. This is usually achieved by adsorbing monomers onto the surface or in a bilayer, or by localizing the initiator near the surface. Surfactants are employed for the colloidal stability of the particles. Modification of the inorganic particle surface enhances the encapsulation efficiency. 

Micro-encapsulation involves stabilizing an emulsion by forming strong films around each droplet. This can be done with a combination of colloidal silica and gelatin as described by Brockett (685). Further study of the interaction of colloidal silica with cationic polymers or with cationic surfactants in oil or polymer emulsions and dispersions in water appears worthwhile, particularly from the standpoint of highly stabilized interfaces. 

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