Colloidal multilayer systems

Abstract Colloidal particles have proved to be a suitable precursor to the formation of nanoscaled materials. More explicitly, they are a suitable way to create photonic band gap materials in 3D. Several methods have been developed to assemble colloidal multilayer systems, and have yielded various levels of success. The vertical deposition method has shown itself to be one of the best in terms of time, control of the final product, crystal size and homogeneity. Despite this, the resulting crystals often present point defects, dislocations, cracks and polycrystallinity, as well... 

Adsorption phenomena from solutions onto sohd surfaces have been one of the important subjects in colloid and surface chemistry. Sophisticated application of adsorption has been demonstrated recently in the formation of self-assembhng monolayers and multilayers on various substrates [4,7], However, only a limited number of researchers have been devoted to the study of adsorption in binary hquid systems. The adsorption isotherm and colloidal stabihty measmement have been the main tools for these studies. The molecular level of characterization is needed to elucidate the phenomenon. We have employed the combination of smface forces measmement and Fomier transform infrared spectroscopy in attenuated total reflection (FTIR-ATR) to study the preferential (selective) adsorption of alcohol (methanol, ethanol, and propanol) onto glass surfaces from their binary mixtures with cyclohexane. Om studies have demonstrated the cluster formation of alcohol adsorbed on the surfaces and the long-range attraction associated with such adsorption. We may call these clusters macroclusters, because the thickness of the adsorbed alcohol layer is about 15 mn, which is quite large compared to the size of the alcohol. The following describes the results for the ethanol-cycohexane mixtures [10],... 

Ryde, N. Kihira, H. Matijevic, E. (1992) Particle adhesion in model systems. 15. Effect of colloid stability in multilayer deposition. J. 

Surface science has been one of the first beneficiaries of self-assembled nanostructures (in the form of SAMs). Self-assembly is a very general strategy for forming molecularly tailored interfaces, and, other than the few systems that have formed the basis for the majority of work in SAMs, almost none of the obvious opportunities to use self-assembly to build ordered, nanostructured interfaces have been examined. The preparation of more sophisticated structures based on molecules with complex stmctures, on self-assembled colloids, on multilayered polymers formed by electrostatic interactions between charged groups166,167, or on biologically derived structures is just beginning168-171. 

UHV systems provided SERS studies with the full power of modern surface techniques. These systems are in principle better controlled and characterized than electrochemical and colloid systems. Thus one can perhaps obtain good evaluations of the coverages and therefore more precise enhancement factors. Another important feature of UHV (and also of film) studies is the possibility of performing experiments where one goes in a controlled manner from submonolayer coverages to multilayers. This can give distance-... 

The term emulsification refers to the technique that involves mixing of two immiscible materials (usually liquids) in order to produce a homogeneous system. Usually, one of the two materials has an oily nature and the second is the water. In the emulsion, the liquid present in the larger proportion is called continuous phase, while the liquid in the smaller proportion, which disperses, is called dispersed phase. Depending on the dispersed phase, there are different types of emulsions, that is, oil-in-water (o/w) wherein oil is the dispersed phase, water-in-oil (w/o) wherein water is the dispersed phase, as well as multiple emulsions, like oil-in-water-in-oil (o/w/o), in which there are continuous layers of the two immiscible materials. Emulsification process includes the use of an emulsifying agent, which will be adsorbed on the interface of the two immiscible materials, in order to achieve the miscibility of them. The structure of these agents contains a polar and nonpolar part, and such molecules may be proteins, phospholipids, etc. Emulsification can also include the use of other colloidal macromolecules, which are able to form multilayer films on the interface, in order to achieve a better kinetic stabilization of the system. ... 

Vesicles are closed bilayers that can be observed in two forms. At low surfactant concentration, the vesicles are unilamellar and behave like a colloidal suspension of polydisperse particles. At more concentrated surfactant solutions, small multilayered vesicles are formed [134], Multilamellar vesicles (known also as spherulites) have also been observed in the lamellar phases of surfactant-brine (or even pure water-alcohol) systems [218]. The surfactant may be SDS [218,223] or DDAB (didodecyldimethylammonium bromide) [224]. In alcohol-containing systems the bilayer structural transformations are controlled by the alcohol/surfactant ratio [134].Thus, in many SDS-brine (or water)-alcohol systems, a vesicle (L4) phase is located between the micellar phase and the lamellar (L ) phase. At fixed surfactant concentration, the sequence of phases L4 -La-L3 (in water) is obtained by increasing the alcohol content, and the sequence L2 -La-L3 (in oil) is obtained by decreasing the alcohol content [ 134]. 

IPECs are of considerable interest because of their numerous promising (potential) applications in agriculture, water treatment, biotechnology, and medicine. Some examples include effective and available binders for dispersed systems and flocculants of colloidal dispersions [2], biocompatible coatings [3, 4], components of membranes [5-11], carriers of biologically active compounds (including enzymes and DNA) [12-16], matrices for metal ions and metal nanoparticles [17-22], and the formation of multilayered PE films and capsules using layer-by-layer techniques [23-32]. 

Studies on PEM are of interest because of the versatility of multilayer formation process with respect to variety of support materials, combination with other assembly techniques and possibility of incorporation of different functional species [1-4]. PEM are applied in chemical and biochemical sensing or preparation of new biomaterials. When colloidal particles or emulsion droplets are used as cores for polyelectrolyte deposition one can obtain hollow micro- and nanocapsules. Such capsules have potential as drug delivery systems [5] capable of sustained release [6,7], microreactors [8,9] or catalytic systems [8-10]. Detailed summaries on the properties and application of PEM prepared by LbL technique can be found in [1,11]. 

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