Bottom self-assembly

Fig. 7 (a) Top Structure (PEG refers to PEG17) and molecular model (hydrophobic core, PEGs are omitted for clarity) of 4. Bottom Self-assembly pattern of 4 (alternate molecular units are given in different colors), (b) Top Cryo-TEM image of a solution of 4 (10 M) in water/THF (7 3 v/v) showing tube-like fibers. Bottom Two views of the overlay of the SAXS molecular envelope (in transparent surface mode calculated from SAXS data obtained for the same solution of 4) and the molecular model of 4 [55]... 

Figure Bl.22.3. RAIRS data in the C-H stretching region from two different self-assembled monolayers, namely, from a monolayer of dioctadecyldisulfide (ODS) on gold (bottom), and from a monolayer of octadecyltrichlorosilane (OTS) on silicon (top). Although the RAIRS surface selection rules for non-metallic substrates are more complex than those which apply to metals, they can still be used to detemiine adsorption geometries. The spectra shown here were, in fact, analysed to yield the tilt (a) and twist (p) angles of the molecular chains in each case with respect to the surface plane (the resulting values are also given in the figure) [40].

The top down approach refers to physically assembling the nanoparticles into desired forms the bottom up approach utilizes specific intermolecular interactions to cause the nanomaterials to self-assemble. 

Tailoring block copolymers with three or more distinct type of blocks creates more exciting possibilities of exquisite self-assembly. The possible combination of block sequence, composition, and block molecular weight provides an enormous space for the creation of new morphologies. In multiblock copolymer with selective solvents, the dramatic expansion of parameter space poses both experimental and theoretical challenges. However, there has been very limited systematic research on the phase behavior of triblock copolymers and triblock copolymer-containing selective solvents. In the future an important aspect in the fabrication of nanomaterials by bottom-up approach would be to understand, control, and manipulate the self-assembly of phase-segregated system and to know how the selective solvent present affects the phase behavior and structure offered by amphiphilic block copolymers. 

Ruiz-Hitzky, E., Aranda, P. and Darder, M. (2007) in Bottom-Up Nanofabrication Supramolecules, Self-Assemblies, and Organized Films (eds. Ariga, K. and Nalwa, H.S.) American Scientific Publishers 9,... 

Figure 6.8 Phthalocyanine 63 self-assembles in chloroform to give bundles of micrometer length fibers. Single fibers have diameter of 50 A (highlighted between arrows) and can be envisaged as nanowires (top left). Chiral derivative 64 forms left-handed super helices (top right) due to chirality within side chains. This chiral expression can be turned-off by addition of K+ ions, which bind within the crown-ether part of the molecule, forcing the phthalocyanines to be stacked directly on top of each other, resulting in straight wires (bottom left).

In practice, as the properties of a (nano)material emerge from the composition, size, shape and surface properties of these individual building-blocks as well as self-assembled architectures made from these building-blocks, chemists are increasingly able to synthesize tailor-made materials from the bottom up. Such techniques generally rely on... 

Abstract This article is a review of the chemical and physical nature of patternable block copolymers and their use as templates for functional nanostructures. The patternability of block copolymers, that is, the ability to make complex, arbitrarily shaped submicron structures in block copolymer films, results from both their ability to self-assemble into microdomains, the bottom-up approach, and the manipulation of these patterns by a variety of physical and chemical means including top-down lithographic techniques. Procedures for achieving long-range control of microdomain pattern orientation as well... 

The formation of bottom-up block copolymer patterns within or on top-down substrate patterns is the basis for so-called templated self-assembly processes, in which long-range order and orientation of microdomain patterns can be imposed by a template or guide . These top-down templates can take a variety of forms including periodic thickness profiles and chemically patterned surfaces. 

Figure 3. Critical concentration behavior of actin self-assembly. For the top diagram depicting the macroscopic critical concentration curve, one determines the total amount of polymerized actin by methods that measure the sum of addition and release processes occurring at both ends. Examples of such methods are sedimentation, light scattering, fluorescence assays with pyrene-labeled actin, and viscosity measurements. Forthe bottom curves, the polymerization behavior is typically determined by fluorescence assays conducted under conditions where one of the ends is blocked by the presence of molecules such as gelsolin (a barbed-end capping protein) or spectrin-band 4.1 -actin (a complex prepared from erythrocyte membranes, such that only barbed-end growth occurs). Note further that the barbed end (or (+)-end) has a lower critical concentration than the pointed end (or (-)-end). This differential stabilization requires the occurrence of ATP hydrolysis to supply the free energy that drives subunit addition to the (+)-end at the expense of the subunit loss from the (-)-end.

A new methodology, which combines traditional (top-down) lithography and self-assembly (bottom-up) approaches, has been developed for fabrication of complex nanoscale colloidal stmctures on a surface over a large domain. The principle of this method is to create a chemically patterned surface by well-established soft lithography, followed by self-assembling nanoparticles selectively deposited... 

Polymer-mediated self-assembly of nanoparticles provides a versatile and effective approach for the fabrication of new materials. This bottom-up strategy builds up nanocomposite materials from diverse nanosized building blocks by incorporation of molecular-level recognition sites. The flexibility and reversibUity of self-assembly processes imparted by specific molecular interactions facilitates the formation of defect-free superstmctures, and it can be further explored in fields ranging from electronics to molecular biology. 

Figure 14.4 Primary sequence and molecular model of a coiled coil dimer and self-assembled polymer with the hydrophobic interface highhghted. The final bundle fiber structure is shown at the bottom. Reprinted from Wagner et al. (2005). Copyright 2005 National Academy of Sciences.

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