Browsing by Subject "Conducting polymers"

Now showing 1 - 9 of 9

Open Access
Core/shell-structured, covalently bonded TiO2/poly(3,4-ethylenedioxythiophene) dispersions and their electrorheological response: The effect of anisotropy
(Royal Society of Chemistry, 2015) Erol, O.; Unal, H. I.
As a new electrorheological (ER) material, core/shell nanorods composed of a titania core and conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) shell were prepared via covalent bonding to achieve a thin polymer shell and make the interfacial interactions between the two components more impressive. The successful coating of PEDOT on the nanorod-TiO2 particles was confirmed by TEM analysis. The antisedimentation stability of the core/shell nanorod-TiO2/PEDOT particles was determined to be 100%. The ER properties of the materials were studied under controlled shear, oscillatory shear and creep tests. The dielectric spectra of the dispersions were obtained to further understand their ER responses and fitted with the Cole-Cole equation. The ER behavior of the dispersions was also observed using an optical microscope. The flow curves of these ER fluids were determined under various electric field strengths and their flow characteristics examined via a rheological equation using the Cho-Choi-Jhon (CCJ) model. In addition, the results were also compared with nanoparticle-TiO2/PEDOT. It was concluded that the conducting thin polymer shell and elongated structure of the hybrid material introduced a synergistic effect on the electric field induced polarizability and colloidal stability against sedimentation, which resulted in stronger ER activity, storage modulus and higher recovery after stress loadings when compared to nanoparticle-TiO2/PEDOT. © The Royal Society of Chemistry.
Open Access
Does the donor-acceptor concept work for designing synthetic metals? III. theoretical investigation of copolymers between quinoid acceptors and aromatic donors
(2006) Salzner, U.; Karaltı, O.; Durdaǧi, S.
Homopolymers of quinoxaline (QX), benzothiadiazole (BT), benzobisthiadiazole (BBT), thienopyrazine (TP), thienothiadiazole (TT), and thienopyrazinothiadiazole (TTP) and copolymers of these acceptors with thiophene (TH) and pyrrole (PY) were investigated with density functional theory. Theoretical band-gap predictions reproduce experimental data well. For all but six copolymers, band-gap reductions with respect to either homopolymer are obtained. Four of the acceptors, BBT, TP, TT, and TTP, give rise to copolymers with band gaps that are smaller than that of polyacetylene. BBT and TTP copolymers with PY in 1:2 stoichiometry are predicted to be synthetic metals. Band-gap reductions result from upshifts of HOMO energies and much smaller upshifts of LUMO values. The smallest band gaps are predicted with TTP, since changes in LUMO energies upon copolymerization are particularly small. The consequence of the small interactions between LUMO levels of donor and acceptor are vanishingly small conduction bandwidths. © Springer-Verlag 2006.
Open Access
The formation and characterization of cyclodextrin functionalized polystyrene nanofibers produced by electrospinning
(2009) Uyar, Tamer; Havelund, R.; Hacaloglu J.; Zhou X.; Besenbacher F.; Kingshott P.
Polystyrene (PS) nanofibers containing the inclusion complex forming beta-cyclodextrin (β-CD) were successfully produced by electrospinning aimed at developing functional fibrous nanowebs. By optimization of the electrospinning parameters, which included varying the relative concentration of PS and β-CD in the solutions, bead-free fibers were produced. Homogeneous solutions of β-CD and PS in dimethylformamide (DMF) were used with concentrations of PS varying from 10% to 25% (w/v, with respect to DMF), and β-CD concentrations of 1% to 50% (w/w, with respect to PS). The presence of β-CD facilitated the production of bead-free PS fibers even from lower polymer concentrations as a result of the higher conductivity of the PS/CD solutions. The morphology and the production of bead-free PS/CD fibers were highly dependent on the β-CD contents. Transmission electron microscope (TEM) and atomic force microscope (AFM) images showed that incorporation of β-CD yielded PS fibers with rougher surfaces. Thermogravimetric analysis (TGA) and direct insertion probe pyrolysis mass spectroscopy (DP-MS) results confirmed the presence of β-CD in the PS fibers. X-ray diffraction (XRD) spectra of the fibers indicated that the β-CD molecules are distributed within the PS matrix without any phase separated crystalline aggregates up to 40% (w/w) β-CD loading. Furthermore, chemical analyses by Fourier transform infrared (FTIR) spectroscopy studies confirm that β-CD molecules are located within the PS fiber matrix. Finally, preliminary investigations using x-ray photoelectron spectroscopy (XPS) and time-of-flight static secondary ion mass spectrometry (ToF-static-SIMS) show the presence of the cyclodextrin molecules in the outer molecular layers of the fiber surfaces. The XPS and ToF-SIMS findings indicate that cyclodextrin functionalized PS webs would have the potential to be used as molecular filters and/or nanofilters for the purposes of filtration/purification/separation owing to surface associated β-CD molecules which have inclusion complexation capability. © 2009 IOP Publishing Ltd.
Open Access
Investigation of charge carriers in doped thiophene oligomers through theoretical modeling of their UV/Vis spectra
(2008) Salzner, U.
The nature of the charge carriers in conducting organic polymers (COPs) is a long standing problem. Polythiophene is one of the prototypes of COPs and intensively studied. Because doping leads to changes in UV/vis spectra that are characteristic of the absorbing species, UV/vis spectra of charged thiophene oligomers with up to 25 rings were calculated with time-dependent density functional theory. The credibility of the method was established by comparing the results with a variety of theoretical levels and with experiment. Effects due to counterions (Cl3-) and solvent (CH 2Cl2) were examined. It was found that TDDFT employing hybrid functionals is accurate enough to distinguish the absorbing species. The findings offer an explanation for the experimentally observed difference in UV-spectra of medium-sized and long oligomers upon doping. As chain lengths of the oligomers increase and energy levels get closer, configuration interaction leads to additional absorption peaks in the high energy sub-band region (at around 1.5-2.5 eV). Thus, long oligomers do not behave differently from medium-sized ones upon doping, only their spectra are different. At low doping levels radical cations (polarons) are produced. At higher doping levels, dications that harbor weakly interacting polaron pairs are formed. Bipolarons are predicted only on very short chains or at high doping levels. There is no bipolaron binding energy and disproportionation of monocations into dications and neutral species is energetically unfavorable. © 2008 American Chemical Society.
Open Access
Investigation of electrochromism process through ultrafast broadband spectroelectrochemistry
(2021-01) Zakaria, Musah
Electrochromism is the reversible change in color of an electroactive material due to a redox reaction induced by the application of voltage. Electrochromic materials have gained much research attention since the discovery of organic conducting polymers in the late 1970s, with high prospects for diverse applications. Color change in electrochromic materials involves two processes. First, a redox reaction that leads to the oxidation or the reduction of the EC material. Then the intercalation of counter-ions into the material for charge balancing. For instance, to effect a color change in a neutral conducting polymer through oxidation, first, an oxidizing potential is applied and the polymer loses electrons in a heterogeneous electron transfer leading to a net positive charge creation. To achieve further oxidation, electroneutrality is partially restored by anions that diffuse from the bulk solution into the polymer. Since the diffusion rate of counter-ions is much slower than electron transfer, it is widely assumed that the oxidation process is rate-limited by ion transport. The main aim of this work is to put this assumption to test. Relying on the fact that heterogeneous electron transfer is much faster than ionic charge transfer, experiments at very short time scales down to a few microseconds are performed. Under such experimental conditions, counter-ions do not have enough time to move into the electrochromic material and any sign of electrochromism is due to electron transfer. Through Ultrafast Cyclic Voltammetry with online iR compensation, sweep rates in the order of kV/s to MV/s are reached. We used thin films of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) used as the electrochromic material in this work. In monitoring the color change of the polymer film, we employ in situ UV-visible spectroscopy. To keep up with the rapid conversion of the polymer between its redox forms, we collect spectra in aggregate mode where several spectra are averaged into a single spectrum. By using a principal component analysis algorithm, the compound spectra are decomposed and we calculate the time that the polymer spends in each of its redox forms during the Ultrafast Cyclic Voltammetry experiments.
Open Access
Porphyrin cross-linked conjugated polymer nanoparticles-based photosensitizer for antimicrobial and anticancer photodynamic therapies
(John Wiley & Sons, Inc., 2021-09-27) Duah, Ishmeal Kwaku; Khaligh, Aisan; Koç, Ahmet; Akolpoğlu Başaran, Duygu Deniz; Tuncel, Dönüş
We report here the synthesis and characterization of a water dispersible conjugated polymer nanoparticle-based photosensitizer and its application in the antibacterial and anticancer phototherapies. Nanoparticles (CPPN) were synthesized in one-pot by nanoprecipitation method, in which a hydrophobic azide functionalized, red-emitting thiophene-benzothiodiazole based conjugated polymer (CP-AZ) was cross-linked with a hydrophilic, propargylamine functionalized porphyrin (TPP-4AL) through cucurbit[6]uril (CB6) catalyzed azide-alkyne cycloaddition (CB6-AAC) reaction. CPPN demonstrated high stability in aqueous medium for more than a month without any visible aggregation and appeared to be a good photosensitizer with high light-triggered reactive oxygen species (ROS) generation ability. Consequently, CPPN displayed photo-induced biocidal activity against Gram-negative (Escherichia coli, E. coli) and Gram-positive (Bacillus subtilis, B. subtilis and Staphylococcus aureus, S. aureus) bacteria. When bacteria suspension was incubated with CPPN (20 μg ml−1) and irradiated with white light (22 mW cm−2) for 10 min, more than 3.5-log reduction in colony-forming units (CFUs) was recorded for the three model bacteria. CPPN demonstrated minimal dark cytotoxicity against the bacteria. Moreover, the cytotoxicity of CPPN on mammalian cell was studied using MCF-7 breast cancer cell line. The results demonstrated that CPPN is non-toxic to mammalian cells in the dark even at a high concentration of 112.5 μg ml−1 and this feature makes CPPN an ideal photosensitizer.
Open Access
A theoretical approach to the polymerization of N-pyrrolyl ethyl vinyl ether
(1998) Yurtsever, M.; Toppare L.; Yaǧci, Y.
The oligomerization mechanism of N-pyrrolyl ethyl vinyl ether is studied for two different routes of polymerization by using quantum mechanical calculations. Model compounds for oligomerization between monomers and monomer-pyrrole systems are optimized fully via semiempirical methods. By comparing the enthalpy changes of these two processes, it is found that generally the binding of pyrrole groups on the carbon backbone is favoured; however, the self-polymerization is also thermodynamically competitive. These results support the previous experimental evidence. © 1998 Elsevier Science B.V.
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.
Open Access
Tuning the degree of oxidation and electron delocalization of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) with solid-electrolyte
(Elsevier, 2017-10) Vempati, Sesha; Ertaş, Yelda; Çelebioğlu, Aslı; Uyar, Tamer
We report on the effects of ionic interaction on the electronic structure of PEDOT:PSS where the oxidation state of PEDOT is an import aspect for various applications. Additional ionic interactions are introduced and controlled by varying the fraction of poly(ethylene oxide) (PEO). These interactions are balanced against the inherent cohesive forces within each of the polymers constituting intertwined networks. Raman spectra evidenced a peak-shift as high as ∼14 cm−1 for C[dbnd]C vibrational region which suggested increasing degree of oxidation of PEDOT for higher PEO fractions. Changes to the single and bipolaronic absorption bands support the results from the Raman spectra. For highest PEO fraction neutral-PEDOT and lowered bipolaron density is attributed to localization of PEDOT chains within PEO matrix. Interestingly, for higher PEO fractions the electronic density of states (DOS) of HOMO and core-levels (S2p, C1s and O1s) suggested increased degree of oxidation and electron localization on PEDOT. Near and below (∼12 eV) Fermi level, contribution to the O2p and C2p atomic orbitals depicted significantly different DOS. Also we note energetic shift for O2s/C2s and bonding σCC atomic and molecular DOS, respectively. The correlation between some surface and bulk-related properties suggests the uniformity of the blend material which might be vital for the application in electrochemical devices.