Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H20: Electrically and Optically Active Polymers |
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Sponsoring Units: DPOLY Chair: Lynn Loo, Princeton University Room: 321 |
Tuesday, March 17, 2009 8:00AM - 8:36AM |
H20.00001: Polymer Physics Prize Symposium Break
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Tuesday, March 17, 2009 8:36AM - 8:48AM |
H20.00002: Soliton and polaron induced 3D conformational changes in conjugated polymers Andre Leitao Botelho, Xi Lin We perform ab initio calculations on polyacetylene (PA), polypyrrole (PPY), and polyaniline (PANI) to examine the 3D conformational change as a function of injected charge. We find that self-localized solitons and polarons in their ground states are dispersed along the chain to minimize the localized charge Coulomb repulsion and the strain repulsion due to chain terminations. Each polaron in PPY or PANI progressively straightens each chain from their neutral bent state, where PPY and PANI are shown to have analogous conformations due to subsequent twisting along non-collinear axes. Solitons in PA are able to fully utilize the zigzag backbone geometry to minimize Coulomb repulsions, by alternating from one side of the chain to the other. This causes bending in alternating directions, leading to a sinusoidal shape, while maintaining a straight chain axis on average. Since PPY and PANI can change from a coil to a straight rod, these polymers can achieve strains about an order of magnitude higher than PA. [Preview Abstract] |
Tuesday, March 17, 2009 8:48AM - 9:00AM |
H20.00003: Conjugated Polymer based sensor for detecting explosives such as RDX (1,3,5-Trinitroperhydro-1,3,5-triazine) Abhishek Kumar, Robinson Anandkathir, Jayant Kumar Conjugated polymers are an important class of materials and have attracted great scientific interests because of their unique optical and electrical properties. Synthesis of various conjugated polymers has been reported for detecting DNT and TNT. Here, for the first time, we report the synthesis and characterization of a conjugated polymer based on thiophene, Poly[2-(3-thienyl)ethanol $n$-butoxycarbonylmethylurethane] (PURET), for the detection of RDX via fluorescence quenching. The incorporation of judiciously chosen bulky butoxycarbonylmethyl urethane side group in the back bone of polythiophene reduces the aggregation, improves the solubility of the polymer in the organic solvents and quantum yield of fluorescence. We have observed a 15 {\%} decrease of fluorescence in 60 sec in thin films of PURET exposed to the saturated vapor of RDX at room temperature. The large exciton diffusion length and interaction between side group and the quencher molecule are believed to be the reasons for enhanced RDX detection. Sensitivity below 5 parts per trillion (ppt) has been demonstrated for RDX at room temperature. The effect of nanostructures (electrospun nanofibers and stamped 1 D periodic pattern) on sensitivity and response time will also be discussed. [Preview Abstract] |
Tuesday, March 17, 2009 9:00AM - 9:12AM |
H20.00004: Charge-transfer excitons in strongly coupled organic semiconductors Paul-Ludovic Karsenti, Jean-Francois Glowe, Carlos Silva Time-resolved and temperature-dependent photoluminescence measurements on one-dimensional sexithiophene lattices reveal intrinsic branching of photoexcitations to two distinct species: self-trapped excitons and dark charge-transfer excitons (CTX; $\agt 5$\% yield), with radii spanning 2--3 sites. The significant CTX yield results from the strong charge-transfer character of the Frenkel exciton band due to the large free exciton bandwidth ($\sim400$\,meV) in these supramolecular nanostructures. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:24AM |
H20.00005: Highly Conductive Polymer Films by Post-Processing Solvent Annealing and Their Broad Applications in Organic Electronics Joung Eun Yoo, Kwang Seok Lee, Enrique Gomez, Kimberly Baldwin, Yangming Sun, Chang Su Kim, Hong Meng, Yueh-Lin Loo The electrical conductivity of polyaniline (PANI) that is template synthesized with a polymer acid of poly(2-acrylamido-2-methyl-1-propanesulfonic acid), PAAMPSA, is enhanced by more than two orders of magnitude with post-processing solvent annealing. Such solvent annealing allows the conducting polymer to rearrange from the globular structure that is arrested by strong ionic interactions during synthesis to the conformationally more favorable structure that dramatically enhances charge transport. This solvent annealing is general; we demonstrate conductivity enhancement with this process for at least two common classes of conducting polymers, including poly(3,4-ethylenedioxytheophene), PEDOT, as well as PANI. The treated conducting polymer films make efficient source and drain electrodes and anodes for organic thin-film transistors and organic solar cells, respectively. [Preview Abstract] |
Tuesday, March 17, 2009 9:24AM - 9:36AM |
H20.00006: Electrochemical Stability of Polyaniline Beyond pH 9 Jacob Tarver, Joung Eun Yoo, Yueh-Lin Loo Conductive polymer films are promising candidates for solution-based biosensor and organic electrochemical transistor devices. For many conducting polymers, however, stable electrochemical activity often demands restrictively acidic solutions. This need has in turn limited the use of conductive polymers in near-neutral and physiological conditions. Using spectroelectrochemical methods, we studied the stability of polyaniline that is template synthesized on poly(2-acrylamido-2-methyl-1-propanesulfonic acid) as a function of pH. Transitions between the different oxidation states of polyaniline are stable and reversible in solutions as high as pH 10. This range of sustained electroactivity far exceeds that of previously reported polyaniline systems. In comparison, polyaniline that is doped with small-molecule acids loses its electroactivity in solutions beyond pH 4. Immobilization of polyaniline within a polymer acid matrix retards dopant diffusivity and reduces proton mobility. The preservation of local acidic conditions within the film greatly extends the pH range of stable electroactivity. [Preview Abstract] |
Tuesday, March 17, 2009 9:36AM - 9:48AM |
H20.00007: Quadratic Electro-optic Effect in a Novel Nonconjugated Conductive Polymer, iodine-doped Polynorbornene Ananthakrishnan Narayanan, Mrinal Thakur Quadratic electro-optic effect in a novel nonconjugated conductive polymer, iodine-doped polynorbornene has been measured using field-induced birefringence at 633 nm. The electrical conductivity$^{1}$ of polynorbornene increases by twelve orders of magnitude to about 0.01 S/cm upon doping with iodine. The electro-optic measurement has been made in a film doped at the medium doping-level. The electro-optic modulation signal was recorded using a lock-in amplifier for various applied ac voltages (4 kHz) and the quadratic dependence of the modulation on the applied voltage was observed. A modulation of about 0.01{\%} was observed for an applied electric field of 3 V/micron for a 100 nm thick film The Kerr coefficient as determined is about 1.77x10$^{-11}$m/V$^{2}$. This exceptionally large quadratic electro-optic effect has been attributed to the confinement of this charge-transfer system within a sub-nanometer dimension. 1. A. Narayanan, A. Palthi and M. Thakur, J. Macromol. Sci. -- PAC, accepted. [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:00AM |
H20.00008: Quadratic Electro-optic Measurements in Nonconjugated Conductive Polymers, iodine-doped Polyisoprene and Poly($\beta $-pinene) at 1.55$\mu $m Ananthakrishnan Narayanan, Jitto Titus, Mrinal Thakur Exceptionally large near-resonant (at 633nm) quadratic electro-optic effects in nonconjugated conductive polymers, iodine-doped poly($\beta $-pinene) and 1,4-cis-polyisoprene have been previously reported. In this report, we discuss the quadratic electro-optic effects in these polymers at 1.55$\mu $m. The measurements were made using the field-induced birefringence technique. A modulation depth of about 0.1{\%} was observed for a 1 $\mu $m thick sample of doped poly($\beta $-pinene) at an applied field of 1V/$\mu $m. The Kerr coefficient as determined was about 1.6$\times $10$^{-10}$ m/V$^{2}$. For polyisoprene samples the modulation was slightly smaller. These exceptionally large Kerr coefficients at a technologically important wavelength make these polymers promising for guided-wave applications in electro-optics. Techniques for longer-term stability of the samples have been established. The large optical nonlinearities as observed have been attributed to the sub-nanometer confinement of these charge-transfer systems [Preview Abstract] |
Tuesday, March 17, 2009 10:00AM - 10:12AM |
H20.00009: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 10:12AM - 10:24AM |
H20.00010: Ultrasensitive Solution Processed Polymer Photodetectors Xiong Gong, Minghong Tong, Gang Yu, Chan-Long Shieh, Boo Nilsson, Alan Heeger Semiconducting polymeric optoelectronic and electric devices have evolved as a promising cost-effective alternative to silicon-based devices. Organic photodetectors have been the subject due to several inherent advantages. Some of the important advantages of these so-called ``plastic'' electronics include large-area detection, low cost of fabrication, ease of processing and mechanical flexibility. However, there are few reports on organic photodetectors whose performances are comparable with inorganic countparts. will report ultrasensitive solution processed photodetectors fabricated by different semiconducting polymers as the electron donors and various fullerences derivatives and/or inorganic quantum dots as the electron acceptors. Polymer photodetectors with different photo-response and detectivity were demonstrated. One example is that polymer photodetectors have photo-response from 300nm to 1450nm, the detectivity larger than 10$^{12}$ cm Hz$^{1/2}$/W, and linear dynamic range larger than 120 dB. All these values are comparable to or even better than their inorganic counterparts. [Preview Abstract] |
Tuesday, March 17, 2009 10:24AM - 10:36AM |
H20.00011: Twin instability of Peierls distortion and its mechanical consequence on conductive polymer actuation Minghai Li, Andre Botelho, Xi Lin We prove analytically that a one-dimensional metallic chain is subject to two coupled spontaneous conformational relaxations, resulting in the well-known Peierls bond length alternation and an overall chain contraction. Using the Su-Schrieffer-Heeger (SSH) Hamiltonian, a tight-binding version of the Peierls theory, we find in a neutral defect-free polyacetylene chain these two coupled distortions work cooperatively against the backbone elastic deformation. The cooperative bond alternation and chain contraction deformations have two effects, allowing bonds alternate and contract less than the case when deformations are independent and breaking the charge conjugation symmetry which would otherwise be conserved. Making such a deformed neutral chain as the reference, we find that creation of self-localized solitons upon dopings results in spontaneous chain contractions within the self-localized domains where the anti-Peierls distortions are enforced. Our numeric results based on the SSH model and first-principles calculations indicate that chain contractions are proportional to the soliton density at low dopings, and the overall chain length varies non-monotonically with respect to the doping level, reaching a maximum contraction of 0.15{\%} at 5{\%} doping. [Preview Abstract] |
Tuesday, March 17, 2009 10:36AM - 10:48AM |
H20.00012: Soliton migration along \textit{trans}-polyacetylene backbone Minghai Li, Yongwoo Shin, Xi Lin We compute the minimum energy paths and activation barriers for the soliton migration process along trans-polyacetylene backbone via the Su-Schrieffer-Heeger (SSH) model and \textit{ab initio} calculations. Our results confirm the conventional consensus that soliton hops over two CH sites in one single step, maintaining wavefunction nodal structures at intermediate CH sites. Standard SSH parameters give rise to negligible migration barriers, which increases exponentially as the localization width decreases. Favoring the opposite elastic strain as the boundaries, soliton prefers staying at the center of an open chain; this ground state energy increases linearly when the chain length decreases. Starting at the center and moving towards the chain termination, soliton first sees a quadratic wash-board energy landscape when it is far away from the boundary and then smoothly switches to an exponentially increased wash-board energy landscape when it is in the vicinity of the boundary due to its localization width shrinkage. The local minima energy has a larger exponent compared to that of the activation barrier so they cross each other at a certain point, beyond which the barrier disappears and solitons cannot get closer to the boundary. [Preview Abstract] |
Tuesday, March 17, 2009 10:48AM - 11:00AM |
H20.00013: ABSTRACT WITHDRAWN |
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