Mesoscopic structure

Poon W C K and Haw M D 1997 Mesoscopic structure formation in colloidal aggregation and gelation Adv. Colloid Interface Sc/. 73 71-126... 

Nanocones of carbon are found[3] in some areas on the substrate together with tubes and other mesoscopic structures. In Fig. 7 two carbon cones are displayed. For both cones we measure opening angles of 19.0 0.5°. The cones are 240 A and 130 A long. Strikingly, all the observed cones (as many as 10 in a (800 A) area) have nearly identical cone angles -19°. 

In a somewhat wider sense, one can define amphiphiles as molecules in which chemically very different units are linked together. For example, the structures formed by A B block copolymers in demixed A and/or B homopolymer melts and their phase behavior are very similar to those of classical amphiphiles in water and/or oil [13,14]. Copolymers are used not only to disperse immiscible homopolymer phases in one another, but also to create new, mesoscopically structured materials with unusual and interesting properties [15]. 

Mesoscopic structures and phases vesicles and vesicle shapes, structured phases and phase behavior of amphiphilic systems. 

Liquids are able to flow. Complicated stream patterns arise, dependent on geometric shape of the surrounding of the liquid and of the initial conditions. Physicists tend to simplify things by considering well-defined situations. What could be the simplest configurations where flow occurs Suppose we had two parallel plates and a liquid drop squeezed in between. Let us keep the lower plate at rest and move the upper plate at constant velocity in a parallel direction, so that the plate separation distance keeps constant. Near each of the plates, the velocities of the liquid and the plate are equal due to the friction between plate and liquid. Hence a velocity field that describes the stream builds up, (Fig. 15). In the simplest case the velocity is linear in the spatial coordinate perpendicular to the plates. It is a shear flow, as different planes of liquid slide over each other. This is true for a simple as well as for a complex fluid. But what will happen to the mesoscopic structure of a complex fluid How is it affected Is it destroyed or can it even be built up For a review of theories and experiments, see Ref. 122. Let us look into some recent works. 

The terminology is not yet homogeneous. The use of the prefix nano spread out in the 1990s. Until then, the common term used to be mesoscopic structures, which continues to be used. According to a definition by IUPAC of 1985, the following classification applies to porous materials microporous, < 2 nm pore diameter mesoporous, 2-50 nm macroporous, > 50 nm. 

An alternative or additional step to flame annealing is electrochemical or chemical polishing. The fundamental aspects of electropolishing were reviewed recently [185], and a list of polishing procedures and parameters is available [185,186]. This method has been successfully applied to the preparation of gold, silver, and copper electrodes for STM studies [177,180,188]. It is important to note that different mesoscopic structures may arise according to the specific preparation procedures. For example, electropolishing a mechanically prepared Au(lOO) surface followed by... 

FIG. 22. Atomic and mesoscopic structure of the reconstructed and uiuecon-structed Au(lOO) surface. The sharp peak in the voltammogram demarks the phase transition and is physically associated with charging the double layer due to the difference in the pzc of the respective phases. (From Ref. 216.)... 

Membrane simulations were performed with 2, = 4,9, and 15. The mesoscopic structure of the hydrated membrane is visualized in Figure 6.7, revealing a sponge-like structure similar to structures obtained by other mesoscale simulations.ii Together with hydrophilic beads of side chains, water beads... 

MESOSCOPIC STRUCTURES AS AN INTERMEDIATE STAGE BETWEEN MOLECULES (MICRO SCALE) ON THE ONE HAND AND BIOLOGICAL CELLS (MACRO SCALE) ON THE OTHER... 

In the past few years much attention has been drawn to the properties of shot noise in mesoscopic structures. So far experimental studies have been primarily concentrated on ballistic and diffusive systems, with only few exceptions [1, 2] where shot noise in electron tunneling or hopping was investigated. 

Using theoretical and computational techniques, one can identify the mesoscopic structures leading to a requisite function. Once identified, these structural motifs can be used to guide experimental chemical imaging probes. 

The mesoscopic size regime is also relevant to organic chemistry and biochemistry since many biological mechanisms, including information transmission across cell membranes, ribosomal protein synthesis, mitochondrial energy conversion, and enzymatic reactions, occur within complexes at the mesoscopic level. For construction of functional mesoscopic structures from organic and biological components, bottom-up... 

Hierarchic design of assembled structures should be important for preparation of functional mesoscopic structures. Typical examples can be seen in biological systems where tissues of organisms in living systems consist of assemblies of cells with cell membranes composed of self-assembled lipids, proteins, saccharides, etc. Therefore, tissues and organisms can be regarded as (at least) two-level assemblies lipid to... 

Inorganic nanoparticles themselves can be assembled into mesoscopic structures. Dinsmore et al. proposed an approach for the fabrication of solid capsules from colloidal particles with precise control of size, permeability, mechanical strength, and compatibility (Fig. 2.9).44 This unusual mesoscopic structure is called colloidosome and is prepared through emulsion droplets at a water-oil interface. Following the locking together of the particles to form elastic shells, the emulsion droplets were transferred to a fresh continuous-phase fluid identical to that contained inside the droplets. The resultant structures are hollow, elastic shells whose permeability and elasticity can be precisely controlled. 

There are some unique examples of organic-inorganic hybrids in natural systems. Some kinds of protein possess inorganic components at their interior. Because such bio-originated hybrid structures have discrete size and composition, they can be used for preparation of fine mesoscopic structures. For example, ferritin, which is composed of 24 self-assembled peptide subunits and capable of including iron oxide, is a good candidate to fulfill this demand. Yamashita demonstrated use of a ferritin array for preparation of a mesoscopic nanodot array (Fig. 2.11 ).47 A Langmuir... 

As briefly described previously in this chapter, layer-by-layer (LbL) assembly is a versatile method for construction of layered structures from various materials.48,49 Therefore, the LbL technique should be a very useful method for constructing layered mesoscopic structures. The LbL assembly concept was first suggested by Iler,50 but realized and established by Decher and coworkers.51 An outline of this technique is shown in Figure 2.12, where assembly between a cationic polyelectrolyte and anionic... 

Some supramolecular mesoscopic structures remain mere objects of scientific interest because of their low yields. If we prepare materials having mesoscopic structures in useful quantities, such materials would be useful for real applications such as highly selective material separation and storage. 

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