Microcapsules containing water

Makino et al. [63] measured the electrophoretic mobility of four types M1-M4 of hydrophilic gel microcapsules containing water prepared by an interfacial polymerization method. Each type of microcapsules has membranes of different compositions. The results of the analysis of the measured mobilitiy values on the basis of Eqs. (21.128) are given in Figs 21.10 and 21.11. 

Pense, A. M. Vauthier, C. Benoit, J. P. Preparation of microcapsules containing water-soluble amphi-philes by interfacial polycondensation. EP 407257, 1991. 

N. Zydowicz, E. Nzimba-Ganyanad, N. Zydowicz, PMMA microcapsules containing water-soluble dyes obtained by double emulsion/solvent evaporation technique, Polym. Bull. 2002, 47,457-463. 

Frere et al. have reported the synthesis and characterization of PU microcapsules containing water, by interfacial polycondensation using three different diols, viz. 1,5- pentane diol, poly(ethylene glycol)s (PEG 600, PEG 1500, PEG 4200), and two different isocyanates, viz. diphenyl methylene diisocyanate (MDl) and poly(hexa-methylene diisocyanate) [25]. The surfactant used is ABA block copolymer from... 

The transport of disulfoton from water to air can occur due to volatilization. Compounds with a Henry s law constant (H) of <10 atm-m /mol volatilize slowly from water (Thomas 1990). Therefore, disulfoton, with an H value of 2.17x10" atm-m /mol (Domine et al. 1992), will volatilize slowly from water. The rate of volatilization increases as the water temperature and ambient air flow rate increases and decreases as the rate of adsorption on sediment and suspended solids increases (Dragan and Carpov 1987). The estimated gas- exchange half-life for disulfoton volatilization from the Rhine River at an average depth of 5 meters at 11 °C was 900 days (Wanner et al. ] 989). The estimated volatilization half-life of an aqueous suspension of microcapsules containing disulfoton at 20 °C with still air was >90 days (Dragan and Carpov 1987). 

Encapsulation. Immobilization of enzymes by encapsulation within semipermeable structures dates back to the 1970s. There are three fundamental variations of this approach. In coacervation, aqueous microdroplets containing the enzyme are suspended in a water-immiscible solvent containing a polymer, such as cellulose nitrate, polyvinylacetate, or polyethylene. A solid film of polymer can be induced to form at the interface between the two phases, thereby producing a microcapsule containing the enzyme. A second approach involves interfacial polymerization in which an aqueous solution of the enzyme and a monomer are dispersed in an immiscible solvent with the aid of a surfactant. A second (hydrophobic) monomer is then added to the solvent and condensation polymerization is allowed to proceed. This approach has been used extensively with nylons, but is also applicable to polyurethanes, other polyesters, and polyureas. 

Microcapsules containing polymer and pigment were prepared in [299] by dispersing a viscous suspension of pigment and oil-soluble shell monomer forming o/w emulsions. Subsequently, a water-soluble shell monomer was added to the emulsion droplets, encapsulating them via interfacial polycondensation. These microcapsules were then heated for free radical polymerisation of the core monomers. It has been shown that polyvinyl alcohol (PVOH) used as stabiliser reacts with the oil-soluble shell monomers. The decrease of PVOH concentration as result of this interaction leads to coalescence of the particles and to the increase of their equilibrium particle size, however, methods are proposed to prevent the depletion of PVOH. 

Microcapsules containing fish oil with proteins as well were prepared using oil-in-water-in oil (O/W/0) double emulsification followed by gelation method (heat or enzyme) (Cho et al., 2003). The oil phase may be the base to include oil-soluble ingredients. 

Both W/O/W and O/W/O emulsions have attracted considerable attention because of their potential applications in food science [4-7], cosmetics [8-10] and pharmaceutics [11]. In particular, there have been many studies on the pharmaceutical applications of W/O/W emulsions because the internal aqueous droplets can contain water-soluble drugs for controlled release or targetable delivery [12-14]. Solid microcapsules loaded vhth bioactive polymers are also prepared from W/O/W droplets by the solvent evaporation method [15-18]. Other applications studied thus far include the synthesis of shaped polymeric microparticles [19] and the use of the intermediating phase as the permeation membrane in separation technology [20-25]. 

Chung H and Cho G (2004),Thermal properties and physiological responses of vapor-permeable water-repellent fabrics treated with microcapsule-containing PCMs, Textile Research Journal, 74, p. 571. 

Such a product would bait or lure a pest to a capsule, but release the pesticide only when the pest digests or attacks the capsule. Using this method, UF microcapsules containing pesticide were prepared such that the capsule size was very small (-15 pm). The second wall material is formed by mixing appropriate amounts of gelatin, gum arabic, and ethyl cellulose in water. UF microcapsules mixed with peanut oil (as attractant) are added to the second wall material solution which, after stirring for 1 h at 65 °C, was cooled to room temperature and stirred for another hour. The resultant gelatin-based shell material encapsulated both peanut oil and UF microcapsules. 

UF microcapsules containing orange or rose extracts are reported to be most suitable for nonwoven fabrics due to their open structures [57]. Microcapsules containing perfume prepared by coacervation methods using gelatin and gum arable have been reported to be useful in solid soap composition. The perfume is released when the soap is placed in contact with water during use [58]. 

UF microcapsules containing DCPD have been prepared by in-situ polymerization in an oil-in-water emulsion [66]. Different experimental parameters such as agitation speed, temperature and pH have been studied in order to obtain microcapsules with a long shelf-life - that is, microcapsules which are impervious to leakage and diffusion of the encapsulated (liquid) heahng agent for a considerable time. 

The simplest way of inclusion of inorganic nanoparticles in the microcapsule shells is their adsorption. Thus, a usual layer-by-layer assembly technique is used to embed nanoparticles in a capsule shell structure. For example, microcapsules containing various number of metal (silver or gold) nanoparticles were fabricated. Magnetite particles were included into the inner volume of polyelectrolyte capsules to obtain magnetic-driven delivery system. In this case magnetite was adsorbed on the surface of a melamine formaldehyde latex core, then polyelectrolyte layers were placed, after that the core was dissolved. Also microdrops of octane-based iron oxide nanoparticles suspension emulsificated in polyelectrolyte water solution were used as template cores. 

---