Supramolecular films

Thin films of phthalocyanine compounds in general, and those prepared by the LB method in particular, display novel electrical properties (Baker, 1985). The LB technique for depositing mono- and multilayer coatings with well-controlled thickness and morphology offers excellent compatibility with microelectronic technology. Such films have recently been reviewed for their potential applications. The combination of LB supramolecular films with small dimensionally comparable... 

Figure 14.11 Two-step self-assembly process of rod-coil oligomer via mushroom shaped nanostructures into polar supramolecular films. The TEM image represents a top view of such a supramolecular film (Copyright Wiley-VCH Verlag GmbH Co. KGaA. Reproduced by permission).

Sulfonated polyaniline (SPAn) is of interest because of its unusual physical properties and improved processability, and it is easy to process into supramolecular films... 

Elegant results have been achieved by electron-beam exposure of supramolecular films. However, there are a number of drawbacks associated with electron beam lithography that should be borne in mind. First, state-of-the-art electron beam lithography apparatus is fast and very powerful, but it is also expensive and usually requires maintenance by skilled staff. For researchers with a major facility in a neighboring laboratory, it may be a very attractive tool. 

Mayer 1, Nakamura M, Toma HE, Araki K (2006) Multielectronic redox and electrocatalytic supramolecular films based on a tetraruthenated iron porphyrin. Electrochim Acta 52(1) 263-271... 

Abstract The electrostatic Layer-by-Layer (LbL) technique allows the fabrication of polyelectrolyte multilayers that can be considered as a special type of interpolyelectrolyte complexes supported by a template (fluid or soUd). The main characteristic that confers special interest to these interpolyelectrolyte complexes is the simplicity and versatility of the method used for their fabrication, although in some cases this may hide the complex influence of the different physico-chemical variables. The possibility to change ionic strength, pH, temperature, etc. and/or the composition makes possible to control the properties and structure of these systems. Furthermore, the compositional and structural richness of these systems opens multiple possibilities for the fabrication of nano-structured materials with tailored properties for numerous applications (from optical to nanomedical devices). This chapter deal with the physico-chemical background of the fabrication of supramolecular films by the LbL method as well as the key properties that should be managed in order to obtain functional materials following this approach. 

Many supramolecules containing cavities, such as CDs, calixarenes or resorcinarenes may be used in the mass-sensitive sensors. Investigation of gas-sorption of obtained supramolecular films shows how they interact with adsorbed gases of aromatic volatile organic compounds (VOCs), and provides an information on structures of the sensing supramolecular materials. 

A second class of monolayers based on van der Waal s interactions within the monolayer and chemisorption (in contrast with physisorption in the case of LB films) on a soHd substrate are self-assembled monolayers (SAMs). SAMs are well-ordered layers, one molecule thick, that form spontaneously by the reaction of molecules, typically substituted-alkyl chains, with the surface of soHd materials (193—195). A wide variety of SAM-based supramolecular stmctures have been generated and used as functional components of materials systems in a wide range of technological appHcations ranging from nanoHthography (196,197) to chemical sensing (198—201). 

The main supramolecular self-assembled species involved in analytical chemistry are micelles (direct and reversed), microemulsions (oil/water and water/oil), liposomes, and vesicles, Langmuir-Blodgett films composed of diphilic surfactant molecules or ions. They can form in aqueous, nonaqueous liquid media and on the surface. The other species involved in supramolecular analytical chemistry are molecules-receptors such as calixarenes, cyclodextrins, cyclophanes, cyclopeptides, crown ethers etc. Furthermore, new supramolecular host-guest systems arise due to analytical reaction or process. 

Th. Bein (ed.), Supramolecular Architecture. Synthetic Control in Thin Films and Solids, American Chemical Society, Washington, DC,... 

Two approaches to the attainment of the oriented states of polymer solutions and melts can be distinguished. The first one consists in the orientational crystallization of flexible-chain polymers based on the fixation by subsequent crystallization of the chains obtained as a result of melt extension. This procedure ensures the formation of a highly oriented supramolecular structure in the crystallized material. The second approach is based on the use of solutions of rigid-chain polymers in which the transition to the liquid crystalline state occurs, due to a high anisometry of the macromolecules. This state is characterized by high one-dimensional chain orientation and, as a result, by the anisotropy of the main physical properties of the material. Only slight extensions are required to obtain highly oriented films and fibers from such solutions. 

II. SUPRAMOLECULAR LAYER ENGINEERING A. Langmuir Film Engineering... 

In this chapter we describe the basic principles involved in the controlled production and modification of two-dimensional protein crystals. These are synthesized in nature as the outermost cell surface layer (S-layer) of prokaryotic organisms and have been successfully applied as basic building blocks in a biomolecular construction kit. Most importantly, the constituent subunits of the S-layer lattices have the capability to recrystallize into iso-porous closed monolayers in suspension, at liquid-surface interfaces, on lipid films, on liposomes, and on solid supports (e.g., silicon wafers, metals, and polymers). The self-assembled monomolecular lattices have been utilized for the immobilization of functional biomolecules in an ordered fashion and for their controlled confinement in defined areas of nanometer dimension. Thus, S-layers fulfill key requirements for the development of new supramolecular materials and enable the design of a broad spectrum of nanoscale devices, as required in molecular nanotechnology, nanobiotechnology, and biomimetics [1-3]. 

FIG. 14 Schematic illustration of an archaeal cell envelope structure (a) composed of the cytoplasmic membrane with associated and integral membrane proteins and an S-layer lattice, integrated into the cytoplasmic membrane, (b) Using this supramolecular construction principle, biomimetic membranes can be generated. The cytoplasmic membrane is replaced by a phospholipid or tetraether hpid monolayer, and bacterial S-layer proteins are crystallized to form a coherent lattice on the lipid film. Subsequently, integral model membrane proteins can be reconstituted in the composite S-layer-supported lipid membrane. (Modified from Ref. 124.)... 

Molecular calculations provide approaches to supramolecular structure and to the dynamics of self-assembly by extending atomic-molecular physics. Alternatively, the tools of finite element analysis can be used to approach the simulation of self-assembled film properties. The voxel4 size in finite element analysis needs be small compared to significant variation in structure-property relationships for self-assembled structures, this implies use of voxels of nanometer dimensions. However, the continuum constitutive relationships utilized for macroscopic-system calculations will be difficult to extend at this scale because nanostructure properties are expected to differ from microstructural properties. In addition, in structures with a high density of boundaries (such as thin multilayer films), poorly understood boundary conditions may contribute to inaccuracies. 

A series of aggregation structures of bilayer forming azobenzene amphiphiles, CnAzoCmN+Br, both in single crystals and cast films was determined by the X-ray diffraction method and uv-visible absorption spectroscopy. From the relationship between chemical structures and their two-dimensional supramolecular structure, factors determining the molecular orientation in bilayer structure were discussed. Some unique properties based on two-dimensional molecular ordering were also discussed. 

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