Silicone microcapsules

Figure 1.10 Scanning electron micrograph of silicone microcapsules containing an aqueous solution of self-tanning composition (Courtesy G. Habar, Microcapsules-Technologies).

Mason MD, Sirbuly DJ, Carson PJ, Buratto SK (2001) Investigating individual chromophores within single porous silicon nanoparticles. J Chem Phys 114(18) 8119 Miinder H, Andrzejak C, Berger MG, Klemradt U, Liith H, Herino R, Ligeon M (1992) A detailed Raman study of porous silicon. Thin Solid Films 221(l-2) 27 Naumenko D, Snitka V, Duch M, Torras N, Esteve J (2012) Stress mapping on the porous silicon microcapsules by Raman microscopy. Microelectron Eng 98 488... 

Polyamide, collodion (cellulose nitrate), ethylcellulose, cellulose acetate butyrate or silicone polymers have been used for preparation of permanent microcapsules. This method offers a double specificity due to the presence of both the enzyme and a semipermeable membrane. Moreover, it allows simultaneous immobilization of many enzymes in a single step and the surface area for contacting the substrate and the catalyst is large. The need of high protein concentration and the restriction to low molecular weight substrates are the main limitations of enzyme microencapsulation. 

I I let clay is a mixture of microcapsules of aluminum oxides and silicon... 

Syntactic foamed plastics (from the Greek ovvxa C, to put together) or spheroplastics are a special kind of gas filled polymeric material. They consist of a polymer matrix, called the binder, and a filler of hollow spherical particles, called microspheres, microcapsules, or microballoons, distributed within the binder. Expoxy and phenolic resins, polyesters, silicones, polyurethanes, and several other polymers and oligomers are used as binders, while the fillers have been made of glass, carbon, metal, ceramics, polymers, and resins. The foamed plastic is formed by the microcapsular method, i.e. the gas-filled particles are inserted into the polymer binder1,2). 

Membrane-reservoir systems based on solution-diffusion mechanism have been utilized in different forms for the controlled delivery of therapeutic agents. These systems including membrane devices, microcapsules, liposomes, and hollow fibres have been applied to a number of areas ranging from birth control, transdermal delivery, to cancer therapy. Various polymeric materials including silicone rubber, ethylene vinylacetate copolymers, polyurethanes, and hydrogels have been employed in the fabrication of such membrane-reservoir systems (13). 

These additives can also be placed into microcapsules with a thin polymer skin. For example, they are filled with natural aromas and applied to the textile from a water dispersion in combination with a polyurethane or silicone binder. The ratio of micro bubbles to binder determines the efficiency and permanence of the finish. Good results after 4-12 washing cycles are reported. The encapsulated materials are released during wearing as the micro bubbles burst from rubbing caused by body movement or by diffusion through the thin layer of the capsules. A market available encapsulation in micro bubbles, built from chitosan, is described by Hampe. The incorporation and controlled release of fragrance compounds is also provided by the sol-gel nano-technique described in Section 18.4. 

The multilayer coating of particles and formation of ultrathin microcapsules were verified by confocal laser scanning microscopy (CLSM, Leica) and atomic force microscopy (AFM, NanoScope). For AFM measurements, a drop of each sample was deposited onto the silicon support (with a PEl/PSS sublayer) and dried. For CLSM analysis, the coated particles and multilayer capsule suspensions were preliminary colored with rhodamin C. 

The experiment with the microcapsules was carried out again using a syringe vessel. In this case, only the specimen was enclosed in the syringe, without any silicone oil, so that the change of total volume including the microcapsules and leaked gas could be measured. Because the PVT tests started after pressurization, the gas expanded under a set pressure. The volume fraction of the microcapsules in the syringe was 75%. 

Fig. 34.8 shows the volume expansion of the specimens. With the temperature of the silicone oil near the specimen as the parameter, the volume changes are plotted as a function of the weight fraction of the microcapsules. The expansion of the unfilled adhesive was less than that of the epoxy filled with microcapsules. The volume increase starts at 60 °C and almost levels around 110°C. Obviously, the final volume expansion depends on the weight fraction of the microcapsules. In the case of 50 wt.% of microcapsules, the final expansion was... 

Ai, Q.-S. Zhang, Q.-Y. Xing, R.-Y. Zhang, J.-P. Direct in-situ polymerization for preparing microcapsules based on reactive ethylene silicone oil encapsulated by poly(urea-formaldehyde). Zhongguo Jiaonianji (2010), 19(4), 13-17. 

Microcapsules containing a small amount of additives that will be released by crack propagation or other triggering mechanisms have been incorporated into polymeric coatings [21]. Urea/formaldehyde capsules containing silicone oil are shown in Figure 21.6. 

Figure 21.6 Urea-formaldehyde microcapsules containing silicon oil. (Courtesy of Dr K. Park, NJ Institute of Technology, Newark, NJ.)...

A drop-on-demand inlqet technique has been presented that prints onto geometrically-patterned silicon substrates. This enables the controlled fabrication of hemispherical microcapsules. The method opens new paths for controlled encapsulation of liquids into smart microsystems. 

The preparation of double emulsions by using MC emulsification was first reported by Kawakatsu et al. [56]. In the first step, a W/O emulsion, which was used as a feed emulsion, was prepared by conventional homogenization. It was then forced into the microchannel array on a silicon substrate to produce a W/O/W emulsion. Solid-in-oil-in-water (S/O/W) pectin microcapsules were also formed by the gelation of the internal aqueous phase - the pectin solution - using a calcium solution containing Tween 20 as an external water phase. 

In-situ processes such as emulsion, suspension, precipitation or dispersion polymerization and interfacial polycondensations are the most important chemical techniques used for microencapsulation [85-90]. An image of microcapsules with an aqueous core and silicone shell prepared using in-situ polymerization is shown in Figure 1.10. 

Figure 9.4 DTA plots of silicone sol-gel films with or without incorporated microcapsules [1 ]. Curve 1 traditional silicone sol-gel coating. Curve 2 silicone sol-gel composite coating containing organosilicone and ZrOj...

Figure 9.7 SEM images of copper coating containing microcapsules with (a) silicone resin (PVA) (b) lubricating oil (PVA) ...

Microcapsules prepared with silicone resin or lube oil as the core and PVA as the wall were incorporated into the copper-plating bath (for composition, see Table 9.2), and electrolytic co-deposition was carried out at current densities (D(J of 10,... 

The times at which microcapsules began to deposit on the electrode surface during the composite copper-plating are detailed in Table 9.3. The amount of deposited microcapsules was found to be directly related to and to the plating time. Microcapsules with a lube oil core were deposited later than the encapsulated silicone resin under the same D]. This showed that a higher and a longer time would be... 

Raman microscopy has also been widely used to determine the stmcture and overall properties of porous silicon at the nanoscale. In particular, parameters like crystallite size, temperature, and stress in porous silicon have been studied by a combination of micro-Raman and microphotoluminescence spectroscopies (Manotas et al. 1999), as shown in Fig. 6. Besides PS layers and multilayers, more elaborate structures such as microcapsules have also been studied by micro-Raman spectroscopy, aiming at evaluating stress and crystallinity (Naumenko et al. 2012). 

Fig. 8 Oil-containing microcapsule in which an 0/W-type emulsion is fixed by HA gel [62] (the white droplets are made of a silicon oil, which is used as the suspension agent).

Another possible approach is based on cyclodextrins, which are bucket-shaped molecules composed of six to eight glucose units and are enzymatically derived from starch. They have the capability of building protective complexes with a variety of molecules, including cosmetically relevant ones such as menthol and vitamin E. These complexes can be attached to fabrics with the help of an adhesive or a binder, which includes cross-linkable silicones, polyacrylates, polyethylene-vinyl acetate, and polyurethanes. A certain amount of binder, typically 0.25-4.0% of dry matter per weight of fabric, is required to bind the microcapsules, complexes, or loaded particles effectively to the medical textile materials. 

In principle, the formation of the porous matrix around a preformed molecular catalyst (bottle-around-ship) and the construction of the molecular catalyst in a preformed porous material (ship-in-a-bottle) have become two popular strategies for the encapsulation of molecular catalysts since the 1980s. Complexes such as [(BINAP)Ru(p-cymene)Cl)Clj, [(MeDuphos)Rh(cod)]OTf, (Salen)Mn, PrPybox-RuClj, and so on, have been entrapped in a silicon membrane, poly (vinyl alcohol) film, microcapsules, or silica matrix via the in situ formation of the network around the complexes (polymerization and sol-gel process were involved in the network formation) [53-55], However, the catalysts prepared are generally poor in activity, selectivity, and stability. The swelling of the polymer host material and the inhomogeneous cavity formed around the metal complexes may be the main reasons for the low activity and stabihty. In addition, the in situ formation of the... 

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