Microcapsules dispersed systems

Complex Coacervation. This process occurs ia aqueous media and is used primarily to encapsulate water-iminiscible Hquids or water-iasoluble soHds (7). In the complex coacervation of gelatin with gum arabic (Eig. 2), a water-iasoluble core material is dispersed to a desired drop size ia a warm gelatin solution. After gum arabic and water are added to this emulsion, pH of the aqueous phase is typically adjusted to pH 4.0—4.5. This causes a Hquid complex coacervate of gelatin, gum arabic, and water to form. When the coacervate adsorbs on the surface of the core material, a Hquid complex coacervate film surrounds the dispersed core material thereby forming embryo microcapsules. The system is cooled, often below 10°C, ia order to gel the Hquid coacervate sheU. Glutaraldehyde is added and allowed to chemically cross-link the capsule sheU. After treatment with glutaraldehyde, the capsules are either coated onto a substrate or dried to a free-flow powder. 

The carbonless system consists of colorformers and oil-filled microcapsules dispersed within a solid coating. In a typical three-part business form, three kinds of carbonless paper work together as a system to transfer images cleanly and clearly from one sheet to the next (Figure 59.2). 

Cyclodexttins, as cyclic oligosaccharides consisting of glucopyranose, with a UpophUic central cavity and a hydrophilic outer surface, have had a relevant role in the design of dispersed drug delivery systems such as microcapsules (Loftsson and Duchene, 2007). Cyclodextiins ability to increase availability of hydrophobic drag fiom dispersed systems still positions them as attractive excipients. 

Major issues in terms of the functionality of the microcapsules are particle ballooning, the microencapsulation efficiency and the physical stability of the dispersed system after reconstitution of the microcapsules. Particle ballooning may occur when crust formation on the particle occurs during drying due to the... 

The viscosity of the albumin/acacia system under the optimum conditions for maximum coacervate yield was too high to prepare microcapsules, the coacervate phase could not be emulsified into the equilibrium phase [55]. However it is considered that the highly dispersed coacervate systems which form at pH values close to the optimum conditions may be useful for microencapsulation. The coacervate yields obtained for these systems are high (between 80 and 89% w/v, [55]) and these highly dispersed systems appear to be relatively stable in the dispersed state compared to other coacervate systems. It was therefore decided to investigate this coacervate system as a potential microencapsulation system. 

Systematic investigation on HPMC-SDS, HPMC-NaCMC, and (HPMC-SDS)-NaCMC interaction were carried out. The interactions were used to obtain coacervate of controlled rheological properties in ternary HPMC/NaCMC/SDS system consisting of 0.7% HPMC, 0.3% NaCMC and different SDS concentrations. Thus obtained coacervate was deposited at surface of emulsified oil droplets. Emulsion stability was tested. Emulsions were spray drayed in order to obtain powder of oil-containing microcapsules. Dispersion properties of microcapsules and microencapsulation efficiency were investigated. 

The formation of ordered two- and three-dimensional microstructuies in dispersions and in liquid systems has an influence on a broad range of products and processes. For example, microcapsules, vesicles, and liposomes can be used for controlled drug dehvery, for the contaimnent of inks and adhesives, and for the isolation of toxic wastes. In addition, surfactants continue to be important for enhanced oil recovery, ore beneficiation, and lubrication. Ceramic processing and sol-gel techniques for the fabrication of amorphous or ordered materials with special properties involve a rich variety of colloidal phenomena, ranging from the production of monodispersed particles with controlled surface chemistry to the thermodynamics and dynamics of formation of aggregates and microciystallites. 

Microcapsule properties make them attractive materials for a wide variety of practical applications. In the area of catalysts, microcapsules provide semipermeable membranes that are readily produced and dispersed. These properties, along with others, have inspired systems that include synthetic or man-made encapsulated catalysts, such as organocatalysts, metal particles, enzymes, and organometallic... 

This is simply improved methods to form droplets from a needle. The goal is to produce small droplets/microcapsules with low size dispersion (less than 10%) with a good level of production. To avoid broad size dispersion, the liquid flow must be in the laminar regime (avoiding turbulence), thus a relatively low flow rate is required compared to spraying (see below). In most cases, energy is required to reduce the droplet size (from a few millimeters with simple needle). This has led to the following systems. 

In particle production by solvent evaporation, the dmg and polymers are dissolved (solvation) in one organic solvent phase that is not miscible with water. The drug-loaded polymer solution is dispersed in a water phase, yielding an oil in water (O/W) emulsion. The organic solvent partitions into the aqueous phase from which it is removed by evaporation [73]. Usually, double-emulsion techniques are used to prepare the microcapsules. Water/oil/water (W/O/W) or oil/oil/water (0/0/W) systems are prepared by dissolving or dispersing the compound in an aqueous or lipid me-... 

Based on phase-separation mechanisms, coacervation systems can be classified into two general types simple coacervation and complex coacervation. When only one polymer is involved, the process is referred to as simple coacervation, and when two or more polymers with opposite charges are involved, it is referred to as complex coacervation. In both cases, the coacervation takes place just before precipitation from solution. This separated phase in the form of amorphous, liquid droplets constituted the coacervate which is the polymer-rich solution. Deposition of this coacervate around the individual insoluble oil droplets or solid particles dispersed in the equilibrium liquid forms the embryonic capsules, and subsequent gelling of the deposited coacervate results in microcapsules. 

Both interfacial polycondensation and polyaddition involve two reactants dissolved in a pair of immiscible liquids, one of which is preferably water, which is normally the continuous phase, and the other one is the dispersed phase, which is normally called the oil phase. The polymerization takes place at the interface and controlled by reactant diffusion. Researches indicate that the polymer film occurs and grows toward the organic phase, and this was visually observed by Yuan et al. In most cases, oil-in-water systems are employed to make microcapsules, but water-in-oil systems are also common for the encapsulation of hydrophilic compounds. Even oil-in-oil systems were applied to prepare polyurethane and polyurea microcapsules. ... 

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