Browsing by Subject "Aromatic polymers"

Now showing 1 - 4 of 4

Open Access
Density functional theory investigation of substituent effects on building blocks of conducting polymers
(Elsevier, 1999) Salzner, U.
Substituted heterocyclic dimers were calculated employing density functional theory (DFT) and analyzed with the natural bond orbits method (NBO). Substitution in 3- and 4-positions leads to parallel shifting of HOMO and LUMO but does not reduce energy gaps. For bridge dimers, HOMO-LUMO gaps correlate with π-electron densities in the carbon backbone and energy gap reduction correlate with the strength of π-π* interactions from the backbone to the bridging group. Alternating donor-acceptor groups do not reduce energy gaps and lead to systems with average HOMO and LUMO levels compared to the parent molecules.
Open Access
Electronic properties of polypyrrole/polyindene composite/metal junctions
(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.
Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.
Open Access
Genetically encoded conductive protein nanofibers secreted by engineered cells
(Royal Society of Chemistry, 2017-06) Kalyoncu, E.; Ahan, R. E.; Olmez, T. T.; Safak Seker, U. O.
Bacterial biofilms are promising tools for functional applications as bionanomaterials. They are synthesized by well-defined machinery, readily form fiber networks covering large areas, and can be engineered for different functionalities. In this work, bacterial biofilms have been engineered for use as conductive biopolymers to interface with electrodes and connect bacterial populations to electronic gadgets. Bacterial biofilms are designed with different conductive peptide motifs, as the aromatic amino acid content of fused peptide motifs has been suggested to contribute to electronic conductivity by influencing monomer stacking behavior. To select the best candidates for constructing conductive peptide motifs, conductivity properties of aromatic amino acids are measured using two different fiber scaffolds, an amyloid-like fiber (ALF) forming peptide, and the amyloidogenic R5T peptide of CsgA protein. Three repeats of aromatic amino acids are added to fiber-forming peptide sequences to produce delocalized π clouds similar to those observed in conductive polymers. Based on the measurements, tyrosine and tryptophan residues provide the highest conductivity. Therefore, the non-conductive E. coli biofilm is switched into a conductive form by genetically inserted conductive peptide motifs containing different combinations of tyrosine and tryptophan. Finally, synthetic biofilm biogenesis is achieved with conductive peptide motifs using controlled biofilm production. Conductive biofilms on living cells are formed for bioelectronics and biosensing applications.
Open Access
Thermal degradation of polythiophene-natural rubber and polythiophene-synthetic rubber conducting polymer composites
(1997) Hacaloǧlu J.; Yiǧit, S.; Akbulut, U.; Toppare L.
Thermal degradation of conducting polymer composites of polythiophene and rubbers was studied by direct and indirect pyrolysis mass spectrometry techniques. The samples were prepared by electrooxidation of polythiophene using natural rubber or synthetic rubber as the insulating matrix. Presence of decomposition products which were not observed during pyrolysis of pure polythiophene and rubbers, and disappearance of rubber-based pyrolysis mass peaks, together with changes in thermal stability and behaviour, may directly be related to a chemical interaction between the components of the composites. The pyrolysis data were used to propose possible polymerization and degradation mechanisms. © 1997 Elsevier Science Ltd.