Broken microcapsules

Figure 5.15 Plot of percentage broken microcapsules versus pressure (P) (log scale) for two microcapsule samples having the...

Figure 11.18 Microcapsule-based self-reporting material amine cured epoxy coating mixed with microcapsules that contained 2, 7 -dichlorofluorescein (DCF), (a) Schematic of the release of DCF solution from broken microcapsules into a crack or scratch where the dye encounters the amine groups of the resin, resulting in colour change, (h) Colour change of a DCF solution in the presence of an amine, (c) Self-reporting properties of the described material.

Immobilized cells are also used in biotechnology in the production of protein molecules. For example, entrapped hybridoma cells have been used for the production of monoclonal antibodies which are secreted into the microcapsules. This allows for easier collection of the antibodies compared to growing the hybridoma cells directly in the culture medium. The microcapsules are easily separated from the culture medium and broken to collect the antibodies. Isolation of the antibodies from the culture medium involves numerous purification steps, and product is lost during each of these steps to an extent which depends on the efficiency of the process. Live vaccines have been encapsulated. For example. Bacillus Calmette Guerin has been encapsulated in an alginate polylysine-alginate system. 

The microcapsules were found to be most prone to damage from exposure to daylight, where the protective shields were broken and microcapsules deflated (Figure 2.22). Two of the fastness to dayhght tests revealed extremely poor light-fastness properties... 

Small size microcapsules on the paper give sharper image, but are less easily broken by a normal writing instrument. In practice, the upper size limit is ca 20 pm and the lower ca 1-2 pm. Multipart business forms contain up to seven sheets, i.e., one original and up to six copies. For optimum color formation in such a form, sizes of 3-6 pm are recommended. 

FIGURE 18.3 SEM images of shell thickness of broken silica microcapsules doped with aqueous glycerol, obtained from [water + glycerol]/TEOS ratio = 10/1 (a) and 1/1 (b). Aqueous glycerol is homogeneously micro-encapsulated in the capsules core. (Reproduced from Galgali, G. et al Mater. Res. Bullet., 46,2445,2011.)... 

The mechanical strength of microcapsules has been measured using the method described in Section 5.3.2. Loaded pressure is calculated from Eq. (4) (see Section 5.3.2), and the broken ratio is defined as the ratio of the number of microcapsules broken at a given pressure to that of all microcapsules measured. From Figure 5.19 it is clear that the broken ratios for microcapsules with fiber incorporated into the capsule wall are smaller than for microcapsules without fiber. This mechanical strength of microcapsules is increased by the incorporation of fiber into the EPS. 

The use of binders has some drawbacks, however. The amount used should be high enough for a good fixation, but should not disturb the controlled release. A microcapsule covered with a binder may be harder to break, or the binder layer may prevent the release from the fabric after the microcapsule has been broken. Binders may also mask the surface properties of the fibers in the fabric. In order to increase and to ameliorate the use of microcapsules as controlled deHvery vehicles for textiles, microcapsules with reactive shells that bond covalently to the fibers have been developed (e.g., reactive groups used in reactive dyestuffs). Such choice is not unlimited because the microcapsules should be able to withstand the conditions necessary for the binding reaction to occur ... 

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. 

In multiple coatings on paper, a coating of colloidal silica can act as a storage layer for reactive compounds. Thus in a pressure-sensitive coating, a base layer silica retains copper and nickel salts which react and develop color when the microcapsules containing dithiooxamide in the upper layer are broken by pressure (653). 

To achieve line pitch connections, a metal sphere or metal-coated plastic sphere coated with an insulating resin fillers were developed. The insulating resin layer is broken only under pressure to expose the underlying conductive surfaces, referred to as a microcapsule filler- (MCF). A higher filler loading can be achieved with MCFs for fine pitch applications, which avoid creating electrical short circuit conditions between printed circuit features (7,12). A typical cross section of an ACA interconnection with MCF material is illustrated in Figure 2. 

Figure 7. Infrared spectrum of (a) Empty UF microcapsules, (b) broken UF microcapsules loaded with TMPTA and (c) TMPTA monomer...

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