Solid supports polymeric colloids

An important application of metal nanoparticles is their use as catalysts on solid supports or in confined media. When the solution containing metal ions is in contact with a solid support, the ions can diffuse in the pores and adsorb on the surface. Therefore, the penetration of the ionizing radiation enables the in situ reduction of metal ions and then the further coalescence of metal atoms inside the confined volumes of porous materials, such as zeolites, alumino-silica-gels, colloidal oxides such as TiOj or polymeric membranes. 

Another advantage of this enzyme-catalyzed route to colloidal PAn salts is the considerably higher pH that can be employed compared to the previous chemical and electrochemical polymerization methods. Horseradish peroxidase immobilized on chitosan powder as a solid support has also been found to catalyze the H202 oxidation of aniline to a similar PAn/PSS product, opening up the prospect of enzyme reuse and the design of enzyme reactors for PAn synthesis.104... 

In the present section, we cover the two steps for creating stationary phases from colloidal assembly. In the first step, the colloids are assembled into a regular, close-packed structure through the evaporation of the solvent or a flow-through system. As we will see later, the colloidal crystal, when filled with electrophoresis buffer, can be used directly as a solid support for capillary electrophoresis [20,21]. Alternatively, a polymeric structure can be formed around the bead template. After dissolving the beads, one is left with a regular structure of cavities and pores that can also serve as an electrophoresis support [22]. 

An alternate route to assembly of nanoparficles as hollow spheres that does not require a polymerization reaction step is sequential electrostatic assembly. Electrostatic-mediated multilayer assembly of charged particles was first demonstrated by R. Her on planar surfaces, wherein he established the proof-of-principle to deposit particles sequentially onto soUd substrates [25]. Decher advanced this scheme by assembling alternately charged PEs (e.g., polycations and polyanions) onto solid supports. Ever since, this scheme has been used to form capsules by sequential electrostatic deposition of single or multiple coatings of materials on preformed colloidal templates and subsequent removal of the template by calcination or solvent dissolution. This constitutes the LBL method for assembly of hoUow spheres. 

A common method to slip-cast ceramic membranes is to start with a colloidal suspension or polymeric solution as described in the previous section. This is called a slip . The porous support system is dipped in the slip and the dispersion medium (in most cases water or alcohol-water mixtures) is forced into the pores of the support by a pressure drop (APJ created by capillary action of the microporous support. At the interface the solid particles are retained and concentrated at the entrance of pores to form a gel layer as in the case of sol-gel processes. It is important that formation of the gel layer starts... 

The implication of such stimuli-responsive particles as a solid polymer support of biomolecules in the biomedical field is probably due to various factors (1) easiest to prepare via precipitation polymerization (hydrogel particles) or a combination of emulsion and precipitation polymerizations (core-shell particles), (2) the colloidal properties are related to the temperature and to the medium composition (i.e., pH, salinity, surfactant etc.), (3) the adsorption and the desorption of antibodies and proteins are principally related to the incubation temperature, (4) the covalent binding of proteins onto such hydrophilic and stimuli-responsive particles can be controlled easily by temperature, and, finally, (5) the hydrophilic character of the microgel particles is an undeniably suitable environment for immobilized biomolecules. 

Other Components. The smaller the particle size, at a given phase ratio, the more difficult it is to ensure colloidal stability (cf Fig. 5). This means that for aqueous heterophase polymerizations in the order suspension < microsuspension < emulsion < miniemulsion < microemulsion, the stabilizer concentration increases. Contrary to the simple polymerization of st5Tene in water, polymerization recipes for industrially important polymer dispersions comprise up to six monomers, frequently more than two emulsifiers, more than one initiating system, and a few other aids like biocides, defoaming agents, plasticizers for supporting film formation (39). The monomer-to-water ratio is adjusted in such a way that a solid content results typically between 40 and 60% or even higher. The amoimts of surfactants and initiator (mainly peroxodisulfate) are typically between 0.5 and 2% (w/w) relative to the monomers and 0.5% (w/w) relative to water, respectively. 

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