Liquid microcapsules

The development of the preparation processes of liquid microcapsules (see Chapter 5) provides a new opportunity for the application of composite coatings in the protective treatment of metal surfaces. Some liquid substances which possess specific properties can be encapsulated (Fig. 9.1) and used to form composites ei-... 

The electrolytic co-deposition of metals with microcapsules provides excellent wear resistance, corrosion resistance, and self-repairing characteristics, these being due to release of the core materials from the liquid microcapsules. 

Figure 9.6 Particle size distributions of liquid microcapsules.

Table 9.2 Composition and process conditions of the composite copper- and nickel- plating baths containing liquid microcapsules.

Although the mechanism of electrodeposition of soHd particles has been well-described in the literature, Htde attention has been paid to the study of co-deposition behavior of liquid microcapsules. The mechanism of the electrodeposition of Hq-uid microcapsules may also be explained by comparing the mechanism of electrodeposition of solid microparticles. 

It can be concluded from the above-mentioned differential capacitance curve and cathodic polarization curve analyses that the mechanistic model of electrolytic codeposition of Hquid microcapsules is associated with the stable chelation of—OH and -O groups of the wall material (e.g., PVA, gelatin) with metal ions (e.g., Ni ", Cu +), and this gives rise to positively charged microcapsules. This in turn helps to accelerate the electrophoretic migration of microcapsules in the plating solution. The liquid microcapsules were also adsorbed onto the electrode due to the presence of a surfactant. Consequently, it is feasible for microcapsules to enter the electrical double layer at the interface and to become embedded in the co-deposited coating. 

Furthermore, the strength of the waU materials and the different factors associated with electrolytic co-deposition kinetics play additional roles in the development of composite coatings with predetermined properties. Hopefully, future research projects wiU lead to the practical application of liquid microcapsules to improve the properties of metal plating coatings by using this novel technique of electrolytic co-deposition in a variety of aspects. 

Microencapsulation is the coating of small solid particles, liquid droplets, or gas bubbles with a thin film of coating or shell material. In this article, the term microcapsule is used to describe particles with diameters between 1 and 1000 p.m. Particles smaller than 1 p.m are called nanoparticles particles greater than 1000 p.m can be called microgranules or macrocapsules. 

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. 

These two seemingly dissimilar applications have a common basis—both are examples of the pressure-sensitive release of a chemical. How are these products designed Tiny spherical capsules (microcapsules or microspheres) with a glass or polymer shell are filled with a liquid core and glued onto paper. For a scratch-and-sniff ad, the core of the microcapsules contains a liquid with the desired scent for carbonless paper, a liquid ink or dye is encapsulated within the... 

Macro-coating is used mainly to stabilise fragrances or transform them from liquid to free-flowing solid powder. Microencapsulation or nanoencapsulation is the process of enclosing a substance inside a miniature capsule. These capsules are referred to as microcapsules or nanocapsules. The substance inside the capsule can be a gas, liquid or solid. The capsule wall can consist of various materials, such a wax, plastic or biopolymers like proteins or polysaccharides. 

Microcapsules arc used in several film coatings other than carbonless paper. Encapsulated liquid crystal formulations coated on polyester film arc used to produce a variety of display products including ihcrmomelers. Polyester film coated with capsules loaded with leuco dyes analogous to those used in carbonless copy paper is used as a means of measuring line and force pressures. Encapsulated deodorants that release their core contents as a function of moisture developed because of sweating represent... 

On the other hand, the interest towards this field is accounted for by the possibility to create polymeric systems, combining the unique properties of low-molecular liquid crystals and high molecular compounds, making it feasible to produce films, fibers and coatings with extraordinary features. It is well-known that the utilization of low-molecular thermotropic liquid crystals requirs special hermetic protective shells (electrooptical cells, microcapsules etc.), which maintain their shape and protect LC compounds from external influences. In the case of thermotropic LC polymers there is no need for such sandwich-like constructions, because the properties of low-molecular liquid crystals and of polymeric body are combined in a single individual material. This reveals essentially new perspectives for their application. 

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