Encapsulation clays

Samakande A, Sanderson RD, Hartmann PC (2008) Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization. J Polym Sci Part A Polym... 

In the past, many groups have tried to encapsulate clay platelets inside latex particles. This encapsulation poses some extra challenges because of the tendency of the clay platelets to form stacks and card-house structures. Most of the attempts resulted in the so-called armored latex particles, i.e. clay platelets in the surface of the latex. Recently, natural and synthetic clays were successfully encapsulated. The anisotropy of the clay resulted in non-spherical latex particles (Figs. 5 and 6), either peanut-shaped [63] or flat [64]. Clay platelets also turned out to be good stabilizing agents for inverse Pickering emulsion polymerizations [65]. 

Many of the papers described emulsion or miniemulsion polymerization in the presence of unmodified or modified clays (often MMT). The modifieation can be surface modification, edge modification or both. lanchis et al. claimed that they obtained both clay platelets (silylated MMT) inside the latex partieles and on the surface of latex particles. Although the elay was not easily visible in the TEM pictures presented, they indirectly inferred the presence of MMT platelets inside the latex particles by looking at the shape of the latex particles. Snowman morphologies were associated with the encapsulated clay. Recently, reversible addition-fragmentation chain transfer (RAFT)-mediated... 

The method of action of the polymers is thought to be encapsulation of drill cuttings and exposed shales on the borehole wall by the nonionic materials, and selective adsorption of anionic polymers on positively charged sites of exposed clays which limits the extent of possible swelling. The latter method appears to be tme particularly for certain anionic polymers because of the low concentrations that can be used to achieve shale protection (8). 

In these systems, particularly systems such as potassium chloride polymer, the role of bentonite is diminished because the chemical environment is designed to collapse and encapsulate the clays since this reaction is required to stabilize water-sensitive formations. The clay may have a role in the initial formulation of an inhibited fluid to provide the solids to create a filter cake. 

Similar methods of encapsulation are also observed in pillared clays, which were also introduced as catalysts as long ago as the early 1980s. The field has been thoroughly reviewed up to 2000 [65], Layered double hydroxide structures have also been used for the entrapment of metal coordination compounds [66],... 

When supported complexes are the catalysts, two types of ionic solid were used zeolites and clays. The structures of these solids (microporous and lamellar respectively) help to improve the stability of the complex catalyst under the reaction conditions by preventing the catalytic species from undergoing dimerization or aggregation, both phenomena which are known to be deactivating. In some cases, the pore walls can tune the selectivity of the reaction by steric effects. The strong similarities of zeolites with the protein portion of natural enzymes was emphasized by Herron.20 The protein protects the active site from side reactions, sieves the substrate molecules, and provides a stereochemically demanding void. Metal complexes have been encapsulated in zeolites, successfully mimicking metalloenzymes for oxidation reactions. Two methods of synthesis of such encapsulated/intercalated complexes have been tested, as follows. 

Veerabadran, N., Price, R. and Lvov, Y. (2007) Clay Nanotubules for Drug Encapsulation and Sustained Release. Nano Journal, 2, 215—222. 

Rhee, G.-Y., B. Bush, M.P. Brown, M. Kane, and L. Shane. 1989. Anaerobic biodegradation of polychlorinated biphenyls in Hudson River sediments and dredged sediments in clay encapsulation. Water Res. 23 957-964. 

Encapsulation of herbicides within anionic clays was readily identified by the loss of HRMAS NMR signal associated with immobilization of the molecules between clay layers.103 The application of HRMAS to soil samples has been shown to provide important results on the interaction of herbicide and other organic components with the soil matrix, using ID lH HRMAS, selective TOCSY and 2D TOCSY experiments.104 Significant advantages to the HRMAS approach are its reduced samples preparation needs, with no extraction, pre-treatment or purification required. 

Clay samples were rehydrated with deionized water, formed into small tiles (1.5 x 1.5 x 4 cm), dried at 100 °C overnight, and fired in an oxidizing environment to 800 °C. Brick samples were analyzed from four 17th century houses (St John s, St. Peter s, the Priest s House, and Van Sweringen s ordinary), the 1674 State House, and the brick Chapel. All brick and experimental tiles were cleaned by abrading away the outer surfaces, rinsed in DI water, allowed to air dry, and then crushed for encapsulation for INAA. 

Binder In site remediation and waste treatment, binders refer to cement, clays, or other cohesive solid materials that encapsulate and immobilize solid and even liquid wastes. Binders are key components in waste solidification/stabilization. 

Solidification The physical encapsulation of contaminants in clays, cement, or other solid binders so that they may undergo safe disposal in the environment (such as landfilling). In contrast, stabilization refers to the immobilization of contaminants through the formation of chemical bonds between the contaminants and the binders. Solidification and stabilization simultaneously occur in waste treatment and are commonly called solidification/stabilization. 

Solidification/stabilization Refers to reducing the mobility of a contaminant in soils, other solids, or even liquid wastes by mixing them with Portland cement, lime, cement kiln dust, clays, slags, polymers, water treatment sludges, iron-rich gypsum, fly ash, and/or other binders. The process decreases the mobility of contaminants through physical encapsulation (solidification) and chemical bonding between the contaminants and the binders (stabilization). 

Earlier reports [50] showed that vesicles composed of oleic acid can grow and reproduce as oleoyl anhydride spontaneously hydrolyzed in the reaction mixture, thereby adding additional amphiphilic components (oleic acid) to the vesicle membranes. This approach has recently been extended by Hanczyc et al. [51], who prepared myristoleic acid membranes under defined conditions of pH, temperature, and ionic strength. The process by which the vesicles formed from micellar solutions required several hours, apparently with a rate-limiting step related to the assembly of nuclei of bilayer structures. However, if a mineral surface in the form of clay particles was present, the surface in some way catalyzed vesicle formation, reducing the time required from hours to a few minutes. The clay particles were spontaneously encapsulated in the vesicles. The authors further found that RNA bound to the clay was encapsulated as well. 

Solidification refers to techniques that encapsulate the waste, forming a solid material, and does not necessarily involve a chemical interaction between the contaminants and the solidifying additives. The product of solidification, often known as the waste form, may be a monolithic block, a clay-like material, a granular particulate, or some other physical form commonly considered solid. Solidification as applied to fine waste particles, typically 2 mm or less, is termed microencapsulation and that which applies to a large block or container of wastes is termed macroencapsulation [29]. 

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