More Complex Architectures

Although this chapter focuses on colloidal nanocrystals, one of the motivations for preparing materials in this form is the flexibility they offer for further processing and application. In this section, we introduce a few examples in which colloidal nanocrystals were used as building blocks to construct more complex architectures having interesting and potentially useful physical properties. 

Cubic lipid phases have a very much more complex architecture than lamellar and hexagonal phases. Their structural characteristics have been elucidated only very recently, and it has become clear that their subtleties are the key to a variety of biological problems. We will consider those subtleties in some detail. The three fundamental cubic minimal surfaces - the P-surface, the D-surface and the gyroid (or G-surface), introduced in Chapter 1, can all be foimd in cubic lipid-water phases. The lipid bilayer is centred on the surface with the polar heads pointing outwards. Water fills the labyrinth systems on each side of the surface. These cubic phases will be termed Cp, CD and CG/ respectively. It is likely that there are other more complex IPMS morphologies in cubic phases of lipid-water mixtures, as yet uncharacterised. 

Transport of mixtures is more complicated, especially in membrane systems with a more complex architecture and operated with large pressure gradients. In such cases quantitative solutions for permeation and separation efficiency (selectivity) are not available in a generally applicable form. Specific solutions have to be obtained by approximations and by combiiung solutions for limiting cases. The description in this chapter takes account of this situation. 

While multivalency, self-assembly, and template effects provide strategies aiming at generating more and more complex architectures, supramolecular chemistry can also be utilized for controlling reactivity and even catalyzing reactions. Closely related to organocatalysis, supramolecular catalysts [39] accelerate reactions by... 

Proteins can spontaneously adsorb on many electrode materials [176] as schematically shown in Figure 1.5a. The interaction is mainly governed by hydrogen bonds as well as electrostatic, dipole-dipole, or hydrophobic interactions. It is important to take into account spontaneous adsorption on the electrode surface because it might also contribute to the overall current signal of a biosensor based on a more complex architecture. The impact of this effect can be evaluated by performing suitable control experiments. 

Although free radical polymerizations are facile, they do not yield well-defined polymer architectures. Good control over the polymerization, however, is essential to allow the synthesis of more complex architectures which might improve the activity of the polymer peptide hybrid. 

For electrostatic and steric stabilization, the particles can be viewed effectively as colloids consisting of a soft and deformable corona surrounding a rigid core. Colloidal particles with bulk elastomeric properties are also available. These particles, which are generally of submicron size, are developed and used as reinforcement additives to improve the Impact resistance of various polymer matrices [28-30]. The rubber of choice is often a styrene/butadiene copolymer. The presence of chemical groups at the matrix-filler interface leads to improved adhesion between them. Typically, the addition of about 30% by volume of these elastomeric particles increases the impact strength of a brittle glassy polymer like polystyrene by up to a factor of 10. For some applications, particles with more complex architecture have been... 

Halogen halogen interactions have also been used to design even more complex architectures, and the crystal structure determination of 1,3,5,7-tetraio-doadamantane reveals the presence of a 3-D diamondoid-like network established through multiple iodo- dodo interactions [57, 58]. 

The work was extended by Olvera de la Cruz and Sanchez [1986] to block copolymers with more complex architectures. For di-block copolymers the authors confirmed Leibler s results. 

An overview of our original works in the field of precise cylindrical nanoshells (nanotubes, nanospirals, and nanorings) self-formed from Ill-V single crystals and Si/GeSi heterofilms and from metal-semiconductor, metal-metal and hybrid films is presented. New results are described on the formation of spatially periodic structures, open and closed single-crystal 3D nanoshells of various shapes with the minimum radius of curvature of 1 nm, and also on assembling these shells in even more complex architectures. 

As is briefly summarized in Fig. 13 this regeneration approach can be taken also for more complex architectures envisaged in biosensor configurations After binding of the streptavidin layer a layer of biotinylated Fab-fragments of Ad = 2.8nm is formed followed by a layer of HCG-antibodies of Ad = l.Snm. Again injection of free biotin removes the whole complexes and regenerates the free desthiobiotin surface (Fig. 13, left side). 

Living anionic ROP of strained silicon-bridged [l]ferrocenophanes (Section 3.3.3) provides an excellent route to PFS block copolymers with controlled block lengths and narrow polydispersities (PDI<1.1) [82-84]. Diblock, triblock, and more complex architectures are now known for a wide variety of organic, inorganic, or even other polyferrocene coblocks. The prototypical materials prepared in the mid-1990s were the diblock copolymers polyferrocenylsUane-h-polydimethylsiloxane (PFS-fo-PDMS) 3.52 and polystyrene-b-polyferrocenylsUane (PS-i -PFS) 3.54 83j. As shown in Scheme 3.4, initial anionic polymerization of monomer 3.21... 

Other expected further studies will likely assess the nanopattems and the mechanisms of their formation, in thin films of block copolymers with more complex architectures. For instance, the phase behavior of star copolymers is increasingly well described [117]. For enlarging the application openings, more advanced substrates will likely be implemented, like the curved surfaces theoretically considered in recent studies [118, 119]. Efforts will be devoted to the generation of reconfigurable and responsive surfaces, which can adapt to surrounding environments [120], as for instance thermoresponsive nanopattemed surfaces [121]. 

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