Encapsulation of Liquids

Nanocapsules can be formulated from a variety of synthetic or natural monomers or polymers by using different techniques in order to fulfil the requirements of various applications. Both, hydrophobic and hydrophilic liquids are of high interest for encapsulation. So, e.g., either sensitive or volatile substances, as drugs or fragrances have to be encapsulated and protected for applications with a sustained demand of the respective compound. DNA, proteins, peptides or other active substances can be encapsulated in order to target them to specific cells. A further benefit of the polymeric shell is the possibility to control the release from the composite particles and hence the concentration in the environment. 

Besides the layer-by-layer technique, which can be applied with or without the use of sacrificial cores [165,166] and usually requires polyelectrolytes, the miniemulsion technique is a highly suitable and versatile method for the formation of capsule formation with sizes down to 100 nm. Even the formation of inorganic capsules (e.g., [167]) by the miniemulsion polymerization is possible. For the formation of polymeric nanocapsules, three general approaches (see Figs. 16, 17, and 23) can be distinguished  

---

The protection of a chemical species by containing it in small droplets, particles, or bubbles covered by a coating. Example the encapsulation of liquid within vesicles. 

Two distinct controlled release technologies are encapsulation of liquid pesticides and the coating of individual pesticide crystals. Encapsulation of liquid pesticides is an established tool for modem formulators. Commercial microencapsulated pesticide products exist and new developments continue to be made. Coating of individual pesticide crystals without their aggregation is more difficult. While new processes do exist to coat pesticide crystals without aggregation these processes have not yet been utilized to create commercial pesticide products. 

Encapsulation of liquid into polymeric fibers. Reprinted with permission from reference 90. Copyright 2006Wiley-VCH Verlag GmbH Co. KGaA. 

Hamer, M.A., Hendrickson, W.A., and Marti, J.J. 2001. Particulate encapsulation of liquid beads. Patent WO0185138. Avekainc. 

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. 

Langer G, Yamate G (1969) Encapsulation of liquid and solid aerosol particles to form dry powders. J Colloid Interface Sci 29 450... 

An electrospray is generally produced by the application of an electric field to a small flow of liquid from a capillary tube toward a counter electrode. The principles of electrospray as applicable to mass spectrometry and the mechanisms involved have been a subject of intense debate over the last decade and have been addressed even before that. This is evident from the discussions in the 2000 issue of the Journal of Mass Spectrometry (e.g., Mora11), the book by Cole,12 and several reviews.8,10 13 14 Here we present a summary encapsulating the relevant observations and direct the readers to the above articles for a more elaborate account. 

Figure 1.20 Encapsulation of microdroplets of liquid crystals in ORMOSIL matrices results in materials with better transparency and thermal stability than polymer-dispersed liquid crystals. Gel-glass dispersed liquid crystal device switched between the OFF and ON state (thickness 10 pm, 4 x 2 cm, Fp p = 90V). (Reproduced from ref. 45, with permission.)...

Hydrophobic ionic liquids, 26 850, 860-861 Hydrophobicity. See also Superhydrophobicity of silicone fluids, 22 578 of silicones, 22 603 solvent, 20 517 of surfaces, 22 111—112 Hydrophobic materials, encapsulation of, 11 545-546... 

It is noteworthy that the encapsulation of the N -CHs group allowed the dissolution of the guest in organic solvent. This remarkable property can find some application in the field of host-guest recognition processes, where extraction and transport from or through different liquid phases are of interest. Further developments can now be considered in the field of material chemistry. It is conceivable to design a cavitand dimer by lower-rim to low-... 

Microencapsulation means the envelopment of liquid droplets or solid particles with natural or synthetic polymers.The encapsulation of a substance with a polymer membrane is undertaken for various reasons, for example, as protection against moisture, or to obtain delayed dissolution of fertilizers, herbicides, or drugs by microencapsulation with semipermeable membranes. 

The water-in-oil-in-water (w/o/w) emulsion method (Figure 11.4) is the predominant method used for encapsulation of biomacromolecules in these microparticles. Protein solution forms the internal water phase of the w/o/w emulsion. Loading efficiency of the microparticles has not been optimal using water or buffer as an internal phase, so water is sometimes substituted with polymeric liquids, such as low molecular weight polyethylene glycol. The primary emulsion is then added to a secondary liquid phase, forming the secondary emulsion. The solvent for the... 

Each method was generally developed to solve a particular problem encountered by a product development or formulation chemist. The relationships among problems, capabilities, and encapsulation methods are shown. The overview concludes with a list of reasons for encapsulation, such as prevention of oxidation, conversion of liquids to solids and detackification. 

Few works on proteins encapsulation have been presented. A recent study by Young et al. [60] deals with the encapsulation of lysozyme in biodegradable polymer microspheres. A 1-10 pm lysozyme particle suspension in a polymer solution was sprayed into a CO2 vapour phase through a capillary nozzle. The droplets solidified after falling into the liquid phase. By delaying the precipitation in the vapour phase, the larger microparticles obtained were able to encapsulate the suspended lysozyme. The final capsules were in the range of 5 - 70 pm. This work is a nice example of protein encapsulation for microparticle delivery systems. 

---