Chain structure solid state self-assembly

This chapter focuses on polyferrocenylsilanes (PFSs) where iron and silicon are in the main chain. Subsequently, PFS block copolymers will be reviewed. These materials represent an area of rapidly growing interest as a result of their self-assembly into phase-separated metal-rich nanodomain structures in thin films and micelles in block-selective solvents. The resulting nanostructured materials have a wealth of potential applications and recent breakthroughs in this area are discussed. The subject matter of the chapter is divided up into subsections covering PFS homopolymer and block copolymer synthesis, solution and solid-state self-assembly and applications of the latter, which have been extensively developed by ourselves and our collaborators and also by other research groups. 

If the structure of the self-assemblies can be immobilized by crosslinking of the spherical parts (the spherical microdomains in the solid state and the core in solution), the crosslinked products should form the core-shell type copolymers (microspheres) (see Figure 1). In fact, poly[st)u-ene(S)-Z>-butadiene (Bu)-Z>-S] block copolymer micelles with cores of polybutadiene (PBu) blocks in dilute solution were stabilized by crosslinking of the chains in the micellar... 

The examples discussed above illustrate the importance of block copolymer chain segment incompatibilities for the phase separation of bulk materials, combined with the ability to perform chemistry within specific nanoscale domains to impose permanence upon those self-assembled nanostructured morphologies. Each is limited, however, to crosslinking of internal domains within the solid-state assemblies in order to create discrete nanoscale objects. To advance the level of control over regioselective crosslinking and offer methodologies that allow for the production of additional unique nanostructured materials, the pre-assembled structures can be produced in solution (Figure 6.4), as isolated islands with reactivity allowed either internally or on the external... 

Fig. 9.17 Examples of self-assembly of nanoparticles by a) hydrophobic interactions via a shell of unfunctionalized n-alkanes. Depicted is a Schematic 2D Representation of the RS/ Au nanoparticle packing structure in the solid state. Domains or bundles of ordered al-kylthiolate chains on Au particles interdigitate into the chain domains of adjacent particles in order to compensate the free volume of the outer region of the alkyl shell (Reprinted with permission from [146] A. Badia, L. Cuc-cia, L. Demers, et al.,J. Am. Chem. Soc. 1997, 779, 2582-2592. Copyright 1997 American Chemical Society), b) Direct comparison of hydrophobic interactions and chemical bridg-...

The complex formation of PECs and PE-surfs is closely linked to self-assembly processes. A major difference between PECs and PE-surfs can be found in their solid-state structures. PE-surfs show typically highly ordered mesophases in the solid state [15] which is in contrast to the ladder and scrambled-egg structures of PECs [2]. Reasons for the high ordering of PE-surfs are i) cooperative binding phenomena of the surfactant molecules onto the polyelectrolyte chains [16-18] and ii) the amphiphilicity of the surfactant molecules. A further result of the cooperative zipper mechanism between a polyelectrolyte and oppositely charged surfactant molecules is a 1 1 stoichiometry. The amphiphilicity of surfactants favors a microphase separation in PE-surfs that results in periodic nanostructures with repeat units of 1 to 10 nm. By contrast, structures of PECs normally display no such periodic nanostructures. 

Studies of monolayer films have included alcohols and carboxylic acids with hydrocarbon chains of varying length in the range C10-C26 [20, 21]. In the liquid condensed and solid states the 11- isotherms have similar shapes at high surface pressures. These data show that the monolayer in the self-assembled state occupies an area of 0.205 nm per monomer. This result is independent of chain length and provides evidence that the monolayer consists of a close-packed structure with all molecular units oriented with their hydrocarbon chains perpendicular to the interface. Under these circumstances, strong attractive van der Waals forces are present between the hydrocarbon tails. As a result, formation of the solid-state film can be irreversible, so that the film does not break up when the surface pressure is decreased. 

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