Interfacial assembly

Glogowski E, Tangirala R, He JB, Russell TP, Emrick T. Miciocapsules of PEGylated gold nanoparticles prepared by fluid-fluid interfacial assembly. Nano Lett 2007 7 389-393. 

Skaff H, Lin Y, Tangirala R, Breitenkamp K, Boker A, Russell TP, Emrick T. Crosslinked capsules of quantum dots by interfacial assembly and ligand crossUnking. Adv Mater... 

Another example of ET in an inhomogeneous medium is the three-zone interfacial assembly depicted in Figure 3.27. To model As for ET between a film-modified metal electrode and a ferrocene/ferrocenium redox couple in contact with aqueous solvent [49], the Poisson equation was solved with the following parameters s = 1.8 and 0I = 78.0 (water) = s0ll = 2.25 (alkane film) = eom = oo (metal), a = d = 3.8 A (effective radius of redox group), and Aq = e [23]. 

As illustrated in Figure 3.2, when the microelectrode is distant from the surface by several electrode diameters, a steady-state current, ij., is observed at the tip. The magnitude of the current is the same as that observed for a microdisk in a conventional experiment. When the tip is near a surface, the tip current, ij, differs from ij.oc, and depends on both the distance between the surface and tip, and the chemical nature of the surface. If the interfacial assembly efficiently blocks electron transfer, i.e. it is an electronic insulator, the mediator will not be regenerated, thus causing to be less than unity. If the Red species becomes re-oxidized at... 

Fluorescence microscopy techniques are now available which are capable of studying supramolecular interfacial assemblies with excellent spatial and temporal resolution as well as exceptional sensitivity. These methods were initially developed for use in cellular biology, but are finding increasing application in interfacial supramolecular chemistry. This trend is set to continue as methods in single-molecule spectroscopy and time-resolved microscopy evolve. 

By their very nature, heterogeneous assemblies are difficult to characterize. Problems include the exact nature of the substrate surface and the structure of the modifying layer. In this chapter, typical examples are given of how surface assemblies can be prepared in a well-defined manner. This discussion includes the descriptions of various substrate treatment methods which lead to clean, reproducible surfaces. Typical methods for the preparation of thin films of self-assembled monolayers and of polymer films are considered. Methods available for the investigation of the three-dimensional structures of polymer films are also discussed. Finally, it will be shown that by a careful control of the synthetic procedures, polymer film structures can be obtained which have a significant amount of order. It will be illustrated that these structural parameters strongly influence the electrochemical and conducting behavior of such interfacial assemblies and that this behavior can be manipulated by control of the measurement conditions. 

As discussed above in Chapter 3, ellipsometry and quartz crystal microbalance (QCM) approaches provide a useful insight into the adsorption of both the supporting interfacial assembly and the proteins themselves. Beyond monitoring the adsorption dynamics and the structural integrity of the biomolecule, the orientation of the active site is of prime importance. For example, if the active site itself binds to the self-assembled monolayer, transport of the substrate or co-enzyme may be blocked. 

Because of the presence of a well-defined energy gap between the conduction and the valence band, semiconductors are ideally suited for investigation of the interfacial interactions between immobilized molecular components and solid substrates. In this chapter, interfacial assemblies based on nanocrystalline TiOz modified with metal polypyridyl complexes will be specifically considered. It will be shown that efficient interaction can be obtained between a molecular component and the semiconductor substrate by a matching of their electronic and electrochemical properties. The nature of the interfacial interaction between the two components will be discussed in detail. The application of such assemblies as solar cells will also be considered. The photophysical processes observed for interfacial triads, consisting of nanocrystalline TiO 2 surfaces modified with molecular dyads, will be discussed. Of particular interest in this discussion is how the interaction between the semiconductor surface and the immobilized molecular components modifies the photophysical pathways normally observed for these compounds in solution. 

The aim of this book is to provide the reader with an overview of interfacial supramolecular chemistry. Supramolecular assemblies of the kind considered in this text are truly interfacial, not only because they separate solid- and solution-phase components but also because they represent the junctions where biology, chemistry, physics and engineering meet. In true interfacial supramolecular systems, individual moieties, e.g. the supporting surface and an adsorbed luminophore, interact co-operatively to produce a new function or property. In addition, these two- and three-dimensional structures remain an important step in the evolution of structure from discrete molecules, to interacting assemblies, and finally to solids. In this last chapter, the future of interfacial assemblies will be briefly considered. This discussion will focus on the possibility of integrating such assemblies into practical devices and the identification of the important scientific challenges. 

Modified TiC>2 surfaces have also found application in the design of fast elec-trochromic devices. The influence of the substrate on the behavior of interfacial assemblies is well illustrated in this book. However, it is important to realize that the electrochromic behavior observed for modified TiC>2 surfaces was not expected. The oxidation and reduction of attached electrochromic dyes are not mediated by the semiconductor itself but by an electron-hopping process, not unlike that observed for redox polymers, where the electrochemical reaction is controlled by the underlying indium-tin oxide (ITO) contact. These developments show that devices based on interfacial assemblies are a realistic target and that further work in this area is worthwhile. 

Other opportunities lie in the investigation of substrates based on p-type semiconductors such as NiO. For p-type materials, electron donation from the valence band to the ground state of the attached molecular component is observed. At present, this process is not well understood and further studies are needed to investigate the behavior of interfacial assemblies based on p-type semiconductors. 

Marken and coworkers examined Ti02 NPs in various types of interfacial assemblies [38,40, 57, 58], In their first study, commercially available 6-nm diameter Ti02 NPs were directly adsorbed onto polished boron-doped diamond electrodes from acidic aqueous solutions containing the Ti02 sol [38]. Using field emission SEM and STM, they observed relatively uniform adsorption of the Ti02 NPs and small... 

Keywords Block copolymer/nanoparticle mixtures Interfacial assembly Nanoparticles Janus particles... 

Besides the basic interest in the parameters governing particle interfacial assembly, there is also considerable technological potential associated with the structures formed at liquid-liquid interfaces. For example, nanoparticles could serve as building blocks for capsules and membranes with nanoscopic pores for filtering or encapsulation and for delivery purposes. 

Consequently, the use of functionalized ligands attached to the nanoparticles is shown to provide an effective means of stabilizing the interfacial assembly by crosslinking. Moreover, the nanoparticle assembly proved to be as elastic and robust... 

Binks and Murakami report unique behavior in NP-induced phase transformation in particle-stabilized air-water systems that is not demonstrated by surfactants. It was seen that by altering silica-NP (20-30 nm) hydrophobicity at constant air water ratio or by changing the air water ratio at fixed NP wettability, phase inversion could be induced from air-in-water to water-in-air foams (Fig. 12) [36]. This investigation thus demonstrates that control over interfacial assembly of NPs leads to the formation of stable NP-shelled hollow spheres, thus resulting in the formation of stable foams, dispersions, and powders with far reaching consequences in opening new avenues for advanced encapsulation (Fig. 13). 

Yunfeng Qiu, Penglei Chen, Minghua Liu. (2008). Interfacial Assembly of an Achiral Zinc Phthalocyanine at the AirAVater Interface A Surface Pressure Dependent Aggregation and Supramolecular Chirality. Langmuir, 24, 7200-7207. 

From these examples, it is clear that self-assembly of facial amphiphiles results in the formation of a variety of common and less common aggregate morphologies. Most notable is the low aggregation number of micellar assemblies and the high degree of order in interfacial assemblies. These properties are related to the large and comparable size of the hydrophobic and hydrophilic surface areas of facial amphiphiles compared to those of classic head/tail amphiphiles. 

Interestingly, nanopartide assembly to form oil-water emulsions can also be performed using nanoparticles obtained from nature, such as vims particles, or more generally protdn-based nanocages referred to as hionanopartides. Such partides are of similar size to many s)mthetic nanopartides and nanorods, yet differ in that their size distribution is uniform, and their ligands consist of the surface-available amino add fimctionality. Examples of bionanopartides that have been reported in oil-water interfacial assemblies indude TMV, cowpea mosaic vims (CPMV), turnip yellow mosaic vims (TYMV), and horse spleen ferritin (HSF). ... 

Characterization of interfaces. The characterization of multicomponent interfacial assemblies, in which structural details on the length scale of angstroms or nanometers determine device function, can be a formidable task. Often in these cases a complete picture of the structure and chemistry of the interface must come from the application of several complementary techniques, in much the same way as a complete description of an elephant requires complementary data from several blind men. 

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