Encapsulated nano-sized particles

Encapsulated Nano-Sized Particles, also Called Overbased Reverse Micelles ... 

At the liquid-solid interface the behaviour of the aggregates will be different depending on their dynamic (true micelles) or static (encapsulated nano-sized particles) character. The dynamic reverse micelles (Figure 4.10) will disaggregate to form molecular adsorbed layers presenting a brush conformation. The molecules interact with the solid surface by their polar heads, often via Coulombian interactions or hydrogen bonding, sometimes by chemisorption. 

As an alternative technique to adsorption experiments, the behaviour at the liquid-solid interface can be advantageously studied by dipping supports (thin carbon layer, mica sheet) into a low concentration dispersion of micelles or encapsulated nano-sized particles in pentane or other light solvent (hexane, toluene, etc.). After removing the solvent, ATEM or AFM can be used to study the films deposited on the chosen surfaces. 

This chapter is concerned with the development of an alternative way to build up the protective tribologic fihn between sliding surfaces that does not imply a chemical reaction of the additive with the substrates in contact. The approach is based on the use of nano-sized particles of tribologic film precursors consisting of reverse micelles or encapsulated mineral particles. First an overview of the various systems that could be used will be presented. Some examples of each case will then be deeply analysed (characterization of the colloidal system, tribologic properties, antiwear film structure and morphology and antiwear action mechanisms). 

Control of the particle size while retaining precise control over the release rate is enabled by compartmentalization of the sol-gel solution into droplets of definite size. This can be achieved by emulsification of the sol-gel solution by mixing it with a solution composed of a surfactant and a non-polar solvent (Figure 2.13). When an active molecule is located in the aqueous droplet of a W/O emulsion, encapsulation occurs as the silicon precursors polymerize to build an oxide cage around the active species. By changing the solvent-surfactant combination, the particle size can be varied from 10 nm to 100 pm as the size of the particles is controlled by the size of the emulsion droplet, which acts as a nano-reactor for the sol-gel reaction (Figure 2.13). 

Properties of nanofillers recently developed nano materials are reported to display greater mechanical strength, greater thermal conductivity and improved electrical performance when compared to materials of normal particle sizes. Nano dimensional materials are being studied as fillers in polymer matrices in a variety of formulations for electrically conductive adhesives, thermally conductive adhesives, encapsulants, printed circuit boards, coatings, catalysts, underfills for flip-chip-attached devices and wafer-level connections. ... 

Much of the work in this area has been done in emulsions having a droplet size of more than 1 pm, and the application of submicron (nano) emulsions in encapsulation of oils and flavors is relatively new in the literature. Some works have been carried out to determine the influence of submicron emulsions produced by different emulsification methods on encapsulation efficiency and to investigate the encapsulated powder properties after SD for different emulsion droplet sizes and surfactants. The process has been referred to as nanoparticle encapsulation since a core material in nanosize range is encapsulated into a matrix of micron-sized powder particles (Jafari et al., 2008). This area of research is developing. Some patents were filed in the past describing microemulsion formulations applied to flavor protection (Chung et al., 1994 Chmiel et al., 1997) and applications in flavored carbonated beverages (Wolf and Havekotte, 1989). However, there is no clear evidence on how submicron or nanoemulsions can improve the encapsulation efficiency and stability of food flavors and oils into spray-dried powders. 

Few years ago this concert of LbL assembling of charged species was transferred to coat micron and sub-micron sized colloidal particles [24-29]. The idea is to employ the nano-engineered properties of multilayers as shell structures formed on colloidal particles. This paper outlines the recent works on step-wise shell formation on various colloidal cores, fabrication and properties of hollow capsules, regulation of capsule wall permeability and approaches to encapsulate different materials into these capsules. 

There is now an increased interest in reducing the size of the encapsulates (from micro- to nano-) in order to minimize their possible impact on food texture and appearance. Reducing the size of encapsulates also creates some extra benefits for specific functional food applications, because of the greater specific surface of the particles generated (for instance, improved adhesion properties). Lipids, polysaccharides and proteins have mostly been used to generate nanoencapsulation systems. 

---