The mixed conductivity behavior of polythiophene-based anionic and cationic polymers is studied under controlled atmospheres in this contribution. The conjugated polyelectrolytes are based on ...regioregular polythiophene backbones with either pendant sulfonate anions or imidazolium cations with counterbalancing tetrabutylammonium hexafluorophosphate and bromide anions, respectively. Direct current, four-point-probe measurements and impedance spectroscopy are performed to separate electronic and ionic conductivity. Optical absorption spectroscopy is used to make statements about the aggregation of the polymer chains and to visualize the electronic doping behavior. Similar to a pure conjugated polymer such as poly(3-hexylthiophene) the electronic conductivity can be tuned over a wide range from below 10−6 S/cm to 2.2 S/cm by external doping with the strong electron acceptor F4TCNQ by sequential solution doping. The ionic conductivity on the other hand is shown to be strongly dependent on the degree of water uptake. We show that values of up to 10−2 S/cm with effective ionic mobilities in the order of 10−8-10−7 cm2/(Vs) can be reached.
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•Mixed conductivity in polymer films is elucidated.•Anionic and cationic polythiophene-based conjugated polyelectrolytes are compared.•Electronic & ionic conductivities are studied under controlled atmospheres.•Ionic conductivities can strongly be tuned via humidity control.•Electronic conductivities can be manipulated upon chemical doping with F4TCNQ.
We highlight the influence of processing conditions on polymorphism and structure formation on the mesoscale for the family of PCPDTBT polymers with branched alkyl side chains. Direct correlations of ...morphology to the chemical structure and to transistor device performance are established. We found that up to four different packing motifs could be realized depending on the polymer derivative and the processing conditions: amorphous, π-stacked, cross-hatched and dimer-containing polymorphs. While C- and F-PCPDTBT display similar packing behavior organizing in π-stacked and dimer-like structures, Si-PCPDTBT gives rise to cross-hatched structures upon simple deposition from solution. The observed differences in chain packing for C-/F-PCPDTBT versus Si-PCPDTBT are attributed to differences in backbone conformations and aggregation behavior in solution. The effect of polymorphism on charge transport is probed using field-effect transistors, in which both π-stacked and cross-hatched polymer chain arrangements yield the highest hole mobilities. Mesoscopic morphology and mobility simulations rationalize our experimental findings by relating mobility to distributions of electronic coupling elements between the chains.
We report on the oxidation potential of partially fluorinated (C42F14H14, F14-RUB) and perfluorinated rubrene (C42F28, PF-RUB) studied by cyclic voltammetry (CV) in solution as well as by ...spectroscopic ellipsometry and near edge X-ray absorption fine structure (NEXAFS) spectroscopy in thin films in combination with density functional theory computations. Due to their different electronic structure, the fluorinated derivatives have a higher oxidation potential and are more stable than rubrene (C42H28, RUB).
We present a systematic study of the morphology and absorption properties of a typical donor–acceptor polymer (PCPDTBT) with semicrystalline behavior in solution and in thin films. In-situ ...spectroelectrochemical data give information about the evolution of the absorption spectra from neutral to charged species. The experimental data are supported by theoretical calculations in the framework of the density functional theory (DFT). Regarding thin film structures, we show that the choice of the solvent has significant influence on the morphology in thin films: whereas CS2 and CHCl3 give rather structureless (amorphous) morphologies, films from 1-CN exhibit a clear crystalline nanofiber morphology. Accompanying UV/vis/NIR spectra of films are highly dependent on the morphology and therefore on the choice of the processing solvent. The absorption of fiber morphologies is strongly red-shifted compared to the structureless films.
We investigate the microscopic mechanisms responsible for microdomain alignment in block copolymer solutions exposed to an electric field. Using time-resolved synchrotron small-angle x-ray ...scattering, we reveal two distinct processes, i.e., grain boundary migration and rotation of entire grains, as the two dominant microscopic mechanisms. The former dominates in weakly segregating systems, while the latter is predominant in strongly segregated systems. The kinetics of the processes are followed as a function of polymer concentration and temperature and are correlated to the solution viscosity.
We report on the thin film phase behavior of poly(styrene)-block-poly(2-vinylpyridine)-block-poly(tert-butyl methacrylate) triblock terpolymers with volume fractions φPS:φP2VP:φPtBMA scaling as ...1:1.2:x, with x ranging from 3.05 to 4. On controlled annealing in the vapor of a nearly nonselective solvent the films form terraces of well-defined thickness with a highly ordered hexagonally perforated lamella structure. Using a gradient combinatorial technique we are able to systematically map the dependence of the morphology on the film thickness. By use of substrates with different surface energy we demonstrate that the perforated lamella is a stable phase, regardless of the chemical nature of the substrate, which makes the structure and methodology robust for application in nanotechnology.
We investigate the microdomain orientation kinetics of concentrated block copolymer solutions exposed to a dc electric field by time-resolved synchrotron small-angle X-ray scattering. As a model ...system, we use a lamellar polystyrene-b-polyisoprene block copolymer dissolved in toluene. Our results indicate two different microscopic mechanisms, i.e., nucleation and growth of domains and grain rotation. The former dominates close to the order−disorder transition, while the latter prevails under more strongly segregated conditions. This conclusion is corroborated by computer simulations based on dynamic density functional theory. The orientation kinetics follows a single-exponential behavior with characteristic time constants varying from a few seconds to some minutes depending on polymer concentration, temperature, and electric field strength. From the experimental results we deduce optimum conditions for the preparation of highly anisotropic bulk polymer samples via solvent casting in the presence of an electric field.
Solvent-Vapor-Assisted Imprint Lithography Voicu, N. E.; Ludwigs, S.; Crossland, E. J. W. ...
Advanced materials (Weinheim),
03/2007, Letnik:
19, Številka:
5
Journal Article
Recenzirano
Sub‐micrometer features are replicated into high‐molecular‐weight polymer resists by using solvent‐assisted nanoimprint lithography (see figure). By swelling the polymer in a controlled solvent‐vapor ...atmosphere, millibar pressures and ambient temperatures are sufficient to achieve high‐fidelity replication.
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