Morphology of microcapsules

The morphology of microcapsules depends mainly on the core material and the deposition process of the shell. Microcapsules may have regular or irregular shapes and, on the basis of their morphology, can be classified as mononuclear, polynuclear, and matrix types (Fig. 1.9). 

Mononuclear (core-shell) microcapsules contain the shell around the core, while polynuclear capsules have many cores enclosed within the shell. In matrix encapsulation, the core material is distributed homogeneously into the shell material. In addition to these three basic morphologies, microcapsules can also be mononuclear with multiple shells, or they may form clusters of microcapsules. 

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FIGURE 47.1 Morphology of microcapsules (a) mononuclear, (b) polynuclear, and (c) matrix. 

Microencapsulation is a process in which liquid or solid is encapsulated by film-forming materials to produce particles with diameters ranging from several micrometers to several millimeters. The process is characterized by the properties of the core material of the microcapsules these properties are well maintained by the core material being separated from the environment by the wall material. Subsequently, and under certain conditions, the core material is released when the wall material is broken. The combination of microencapsulation with traditional coating technology offers a completely new approach to surface protective treatment The preparation techniques involved, together with details of the morphology of microcapsules and their properties are discussed in Chapter 1 of this book. 

The term microcapsule is defined, as a spherical particle with the size varying between 50 nm and 2 mm containing a core substance. Microspheres are, in a strict sense, spherically empty particles. However, the terms microcapsules and microspheres are often used synonymously. In addition, some related terms are used as well. For example, microbeads and beads are used alternatively. Spheres and spherical particles are also employed for a large size and rigid morphology. Due to attractive properties and wider applications of microcapsules and microspheres, a survey of their applications in controlled drug release formulations is appropriate. 

The surface of microcapsules has a granular structure (Fig. 2b). The average size of grains is 84.0 13.0 nm. Such morphology is probably related to... 

Polymea mictocapsules containing 0,0-3,5,6-trichloro-2-pyridyl phosphorothioate (Dursban) were prepared by reacting a polyisocyanate and a poly amine and the factors affecting the formation of the microcapsule wall examined. The formation of polyurea was confirmed by FTIR spectroscopy, the thermal properties of the microcapsules were investigated by DSC and the morphology of the microcapsules detenninedby scanning electron microscopy. Optimum conditions for the formation of a thin surface l er and a porous matrix were established. 9 lefs. 

Journal of Microencapsulation 18, No.6, Nov./Dec. 2001, p.801-9 MORPHOLOGY AND STRUCTURE OF MICROCAPSULES PREPARED BY INTERFACIAL POLYCONDENSATION OF METHYLENE BIS(PHENYL ISOCYANATE) WITH HEXAMETHYLENE DIAMINE Jabbari E... 

The morphology of the resulting solid material depends both on the material structure (crystalline or amorphous, composite or pure, etc.) and on the RESS parameters (temperature, pressure drop, distance of impact of the jet against the surface, dimensions of the atomization vessel, nozzle geometry, etc.)[ l It is to be noticed that the initial investigations consisted of pure substrate atomization in order to obtain very line particles (typically of 0.5-20 m diameter) with narrow diameter distribution however, the most recent publications are related to mixture processing in order to obtain microcapsules or microspheres of an active ingredient inside a carrier. 

FIGURE 11.8 Schematic morphologies of the two types of microcapsules, (a) Core-shell microcapsule or reservoir and (b) matrix type microcapsule. (From Lembo, D. and Cavalli, R., Antivir. Chem. Chemother., 21, 53,2010.)... 

Zhuo, L. Chen, S. Effects of catalyst and core materials on the morphology and particle size of microcapsules. International Journal of Polymeric Materials (2004), 53(5), 385—393. 

The speed in which this exchange occurs determines the final morphology of the membrane or microcapsule. 

FIGURE 32.2 Schematic diagram of microcapsules morphology (a) reservoir system (simple wall) (b) matrix system (c) simple wall (liquid core) (d) multicore (e) simple wall (solid and irregular core) and (f) matrix (solid core dispersed into the polymeric matrix). 

In addition to these three basic morphologies, microcapsules can also be mononuclear with multiple shells, or they may form clusters of microcapsules. 

The formation of microcapsules is greatly affected by the surfactant, which influences not only the mean diameter but also the stability of the dispersion. The surfactants used in the system have two roles, the first one to reduce the interfacial tension between oil and aqueous phases allowing formation of smaller microcapsules and the other one to prevent coalescence by its adsorption on the oil-water interface and therefore by forming a layer around the oil droplets. The synthesis of a core/ shell particle or other possible morphologies is mainly governed by the kinetic factors and thermodynamic factors. 

Ihe morphology of the surfaces of the linked microcapsules via CA was examined after curing. Fig. 7 shows SEM image of EC microcapsules linked on cotton at 110°C using CA as a catalyst. After few minutes curing the microcqjsules are presented on... 

Berg et al. reported the preparation and evaluation of microcapsules formed by the polymerization of methyl methacrylate in the presence of an oil-water macroemulsion. The oil phase was composed of an alkane (e.g., decane or hexade-cane), and the oil-water emulsions were stabilized by a variety of emulsifiers [42,43]. Both oil- and water-soluble initiators were used, and the monomer was introduced by either dissolving in the oil or feeding it through the water phase. The authors view this system to be an opportunity to study morphological characteristics of polymeric microparticles in the 1 to 100 im size range. 

Scanning electron microscopy (SEM) of microcapsules from which HD is extracted have been studied to understand the extent of encapsulation. One-hole, large-hole and half-moon morphologies imply that HD is not encapsulated completely by polymer, whereas a hollow morphology indicates complete encapsulation. Figure 5.8 shows SEM images of polymer microcapsules as a function of HD amount at lower monomer conversion (without DMAEMA). In the absence of DMAEMA, one-hole or... 

Figure 9.2 Morphology of the zirconium oxide sol-gel coating (a) and the zirconium oxide sol-gel composite coating containing microcapsules [1] (b).

Figure 9.9 Surface morphology of copper coating without microcapsules (a) and microcapsules with inhibitor (b).

Figure 9.22 illustrates the morphology of the composite coatings containing microcapsules and normal nickel-plating coatings before and after the wear-resist-... 

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