The molecular-level layer-by-layer processing of polyaniline with a variety of different nonionic water soluble polymers has been demonstrated. This new type of layer-by-layer adsorption process is driven by hydrogen-bonding interactions and has been accomplished with poly(vinylpyrrolidone), poly(vinyl alcohol), poly(acrylamide), and poly(ethylene oxide). FTIR spectroscopy measurements confirm a high level of hydrogen bonding between polyaniline and the nonionic polymer in the multilayer films. The effects of solution pH and polymer molecular weight on the deposition process were investigated. Comparisons with polyaniline films assembled via an electrostatic mechanism with sulfonated polystyrene indicate that the nonionic polymers adsorb onto polyaniline with a greater density of loops and tails and form highly interpenetrated bilayers with a high polyaniline content. The conductivities of these self-assembled multilayer films were found to be on the order of 1−4 S/cm for films doped with methane sulfonic acid. It was also demonstrated that the deposition process could be carried out with mixed solutions of polyaniline and a nonionic polymer.

Multilayer thin films comprised of sequentially adsorbed layers of partially doped polyaniline and a polyanion, sulfonated polystyrene, were fabricated via the use of a simple layer-by-layer molecular-level processing scheme. Using this simple multilayer polymer adsorption process, uniform thin films of polyaniline in the 40−600 Å thickness range were readily fabricated onto a variety of different substrates. Doping of these films with strong acids such as HCl and methane sulfonic acid results in electrically conductive thin films with conductivities comparable to those obtained with spin cast films (0.5−1.0 S/cm). The adsorption process used to fabricate the films was found to be driven primarily by the electrostatic attractions developed between the partially doped chains of polyaniline (polycation) and the negatively charged chains of the polyanion.

Neutron reflectivity has been used to study the organization of self-assembled multilayers of sulfonated polyaniline and polyallylamine. Films were prepared by the sequential adsorption of polycations and polyanions from dilute aqueous solutions. Scattering contrast was achieved by selective deuteration of the blocks of bilayers at varying intervals along the film. The multilayer structure was found to be preserved over 40 bilayer depositions, but with an internal organization which decays monotonically away from the substrate. These results suggest that the observed interfacial widths are primarily due to the accumulation of defects as the bilayers are deposited.

No abstract

Several diacetylenic lecithins form tubular microstructures (tubules) when their liposomes are cooled through the chain-melting transition. Recently, the tubules have been metal plated by an electroless technique. This paper reports on the interaction of permalloy coated tubules with electromagnetic radiation. At 10 vol % loading of tubules in an epoxy matrix has a real dielectric constant ε′≊50 at a frequency of 9.5 GHz. Simple electrodynamics accounts well for the observed results. Far higher values of ε′ may be achievable with longer tubules and with improved metal coatings.

We report the first demonstration of vacuum field emission from an electron source fabricated from self-assembling biomolecular composite microstructures. Diacetylenic lipid DC8,9PC is used to form hollow, 0.5 μm diam, ≳50 μm long, tubelike structures that are subsequently plated with metal and formed into an aligned composite in an epoxy matrix. The composite material is thin-sectioned across the axis of alignment and then etched to expose the plated tubules. The sharp edges of the exposed metal tubules produce a very large local electric field enhancement, allowing for the vacuum field emission of significant current densities at relatively low applied macroscopic fields (≤60–80 kV/cm).

Measurements have been made of the dielectric response of distributions of metallized fibers aligned in epoxy matrices for different loading fractions and fiber lengths. These have been shown to be in reasonable agreement with a simple independent particle theory. Use of the theory allows classification of fiber dielectric behavior by fiber conductivity and a characteristic length. Some aggregation of the fibers has been observed, even at relatively low loading densities. Computer simulation suggests enhanced dielectric constants of the composites for a moderate range of separations where the fibers are offset about 75% of their lengths with respect to each other and are closer than about 10 radii. This effect may be significant for aligned fibers which tend to aggregate in the magnetic field with separations and offsets within this range. The resulting composites are rugged and easily machined, and with less than 5% fiber weight loading have large, highly anisotropic dielectric constants of 60 or more at microwave frequencies in the X band. In conjunction with their (predicted) broadband performance characteristics such media should prove useful for a variety of applications.

Blending polyaniline (PAn) with a host polymer has the advantage of reducing the amount of polyaniline necessary for conductivity, increasing the stability of this conduction, and enhancing the overall mechanical integrity, versatility, and processability of PAn. PAn blends have generally been observed to be immiscible, reducing many of the above mentioned advantages. In this work, PAn was solution blended with poly (vinyl pyrrolidone) (PVP) in either NMP or DMAc, both polar solvents with an amide linkage. We have found PAn to be miscible with PVP under certain processing conditions. The extent of this compatibility and resulting mechanical properties were assessed by DMA, DSC, TGA, SAXS, and light Microscopy. DSC thermograms exhibit a single Tg for all blends ranging from 3 to 30 % by weight PAn. Light Microscopy and SAXS also suggest no phase separation. TGA results show that NMP binds very tightly to both PAn and PVP, with solvent cast blends retaining up to 20 wt% NMP, even after relatively vigorous drying. Electrical conductivity measurements of cast films show conductivity to range from 10-3to 2 S/cm over the same composition range.