Bulletin of the American Physical Society
2008 Spring Meeting of the Ohio-Region Section of APS
Volume 53, Number 3
Friday–Saturday, March 28–29, 2008; Youngstown, Ohio
Session C3: Polymer Physics and Optics |
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Chair: Michael Crescimanno, Youngstown State University Room: Moser Hall 2008 |
Saturday, March 29, 2008 8:24AM - 8:36AM |
C3.00001: Conformation and collapse of a polymer chain in explicit solvent: A solvation potential approach Mark Taylor The conformation of a polymer chain in solution is intrinsically coupled to the chain's local solvent environment. In much of the theoretical work on polymers in solution solvent effects are treated implicitly and explicit chain-solvent coupling is ignored. Although a formally exact treatment of chain-solvent coupling can be constructed, the required many-body solvation potential is not practical to compute. We have recently shown that for short hard-sphere and square-well chain-in-solvent systems this many-body solvation potential can be made tractable via an ``exact'' decomposition into a \textit{set} of two-site potentials [1]. Here we use these exact short chain results, combined with the pure solvent potential of mean force, to construct approximate two-site solvation potentials for long chains under a range of solvent conditions [2]. Monte Carlo simulations for full chain-in-solvent systems verify the accuracy of our solvation potential mapping. We use this approach to study the role of solvent in both driving and inhibiting chain collapse in square-well systems and discuss the possibility of solvent driven chain collapse in the symmetric hard-sphere chain-in-solvent system. [1] M. P. Taylor and G. M. Petersen, J. Chem. Phys. \textbf{127}, 184901 (2007). [2] M. P. Taylor and S. Ichida, J. Polym. Sci., Part B: Polym. Phys. \textbf{45}, 3319 (2007). [Preview Abstract] |
Saturday, March 29, 2008 8:36AM - 8:48AM |
C3.00002: Diffusion and Friction Coefficients of Athermal Polymer Melts Nenad Stojilovic, Jutta Luettmer-Strathmann The dynamics of polymer chains in polymer melts depends on mobility of polymer segments and entanglement effects and, at present, it is a challenge to separate these two effects in simulation studies. We study chain dynamics of athermal polymer melts using Monte Carlo simulations and extract diffusion and friction coefficients. We compare results of two different Shaffer's bond-fluctuation models. In the first model, bonds between polymer segments are allowed to cross each other and as a result chains do not entangle; in the second model, bond crossings are forbidden and entanglement effects play important role. Both models exhibit similar static properties allowing us to separate local friction and entanglement effects. We perform simulations for three different densities and a range of chain lengths and investigate connections between static and dynamic properties of athermal polymer melts. [Preview Abstract] |
Saturday, March 29, 2008 8:48AM - 9:00AM |
C3.00003: Effect of chain stiffness on polymer properties Jutta Luettmer-Strathmann Static and dynamic properties of polymers are affected by the stiffness of the chains. In this work, we investigate structural and thermodynamic properties of a lattice model for semiflexible polymer chains. The model is an extension of Shaffer's bond- fluctuation model and includes attractive interactions between monomers and an adjustable bending penalty that determines the Kuhn segment length. For isolated chains, a competition between monomer-monomer interactions and bending penalties determines the chain conformations at low temperatures. For dense melts, packing effects play an important role in the structure and thermodynamics of the polymeric liquid. In order to investigate static properties as a function of temperature and chain stiffness, we perform Wang-Landau type simulations and construct densities of states over the two-dimensional state space of monomer-monomer and bending contributions to the internal energy. [Preview Abstract] |
Saturday, March 29, 2008 9:00AM - 9:12AM |
C3.00004: All-Polymer Lasers Yeheng Wu, Joseph Lott, Tomasz Kazmierczak, Hyunmin Song, Eric Baer, Kenneth Singer, Christoph Weder We have fabricated all-polymer lasers both as distributed feedback lasers (DFB) and distributed Bragg reflector (DBR) lasers. For the DBR lasers, a layer of polymer doped with the laser dye is laminated between two multilayer polymer mirrors. The mirrors were made using the co-extrusion process combining PMMA alternated with polystyrene with 128 layers for each mirror. Two dyes were employed, Rhodamine 6G (R6G), and 1,4-bis-($\alpha $-cyano-4-methoxystyryl)-2,5-dimethoxybenzene (C1RG). They were pumped with a nanosecond laser and emitted at about 570 and 510 nm respectively. For DFB lasers, the low refractive index layers were doped with C1RG or R6G. PMMA and PMMA-PVDF were the hosts for the C1RG and R6G respectively. A total of eight co-extruded 32-layer films were stacked together to make a DFB laser. For the DBR lasers, we were able to observe thresholds as low as 100nJ. The highest conversion efficiency obtained about 14{\%} in the forward direction. We also observed trends of lasing threshold, even spaced lasing modes and penetration of the film. Matrix method simulations taking into account layer thickness variations were consistent with experimental results. For the DFB lasers, the lowest lasing threshold observed was 52 $\mu $W. [Preview Abstract] |
Saturday, March 29, 2008 9:12AM - 9:24AM |
C3.00005: Observations of the Diffraction Pattern Produced by the Surface Thermal Lensing (STL) Technique Applied to Polymers Daeha Joung, Marshall Thomsen, Donald Snyder In the Surface Thermal Lensing (STL) technique, an intense chopped pump beam irradiates a sample perpendicularly. The result is localized deformation of the surface, a thermal bump, due to thermal expansion. The nature of the thermal bump depends on thermal, optical, and mechanical properties of the sample. If the sample is a polymer, additional orientational changes may take place within the molecules. These various changes are detected using a larger size, weak probe beam focused on the same spot. In inorganic samples, the resulting diffraction pattern in the reflected probe beam is attributed to the thermal bump and the temperature dependence of the index of refraction. We report evidence that in polymer samples, local, polarization dependent variations in the reflectivity may also influence the diffraction pattern. Diffraction patterns with and without polarizers intercepting the probe beam will be discussed, and the results will be compared qualitatively to a simple, one-dimensional diffraction model. [Preview Abstract] |
Saturday, March 29, 2008 9:24AM - 9:36AM |
C3.00006: Multi-photon EIT Toomas Laarits, Bryan O'Gorman, Michael Crescimanno We describe and solve a quantum optics models for multiphoton interrogation of an electromagnetically induced transparency (EIT) resonance. Multiphoton EIT, like its well studied Lambda-system EIT progenitor, is a generalization of the N-resonance process recently studied for atomic time keeping. The solution of these models allows a preliminary determination of this processes utility as the basis of a frequency standard. [Preview Abstract] |
Saturday, March 29, 2008 9:36AM - 9:48AM |
C3.00007: The EIT- and N- joint resonance lineshape asymmetry Michael Crescimanno, Cindy Hancox, Michael Hohensee, David Phillips, Ron Walsworth The solution of a quantum optics model for the joint EIT- and N- resonance explains the experimentally observed two-photon lineshape asymmetry as arising from interference and AC stark effects. This solution is evaluated for various light field intensities, detunings and couplings associated with experiments performed on the D1 and D2 transition of 87Rb. Because of its contribution to clock instability, lineshape asymmetry remains perhaps the main impediment to improving all-optical time standards based on the joint resonance. [Preview Abstract] |
Saturday, March 29, 2008 9:48AM - 10:00AM |
C3.00008: Distributed Fiber-Bragg Grating Temperature Sensors for Real-Time Multiple-Point Temperature Monitoring Corneliu Rablau, Simon Murphy Distributed fiber-optic temperature sensors (DFOTS) are being increasingly deployed in applications requiring 2D or 3D temperature profiling. Fiber Bragg Gratings (FBG's), through the shift of their Bragg wavelength, are well suited for such applications due to their immunity to electromagnetic interference and small physical size and thermal inertia of the sensing element. These characteristics are complemented by the easiness of combining individual gratings in series or parallel arrays that can monitor systems with characteristic dimensions from as small as a few millimeters to as large as several kilometers. To highlight this versatility, we report on the study of two FBG arrays for temperature monitoring. A series array obtained by inserting several discrete FBG's operating at different Bragg wavelengths on a 5-km long fiber strand is used to monitor the temperature at predetermined points along the fiber link. A second, parallel array of FBG's is used to monitor the temperature in a cross-section of a 3 ml vial containing a ferrofluid in magnetic field. The temperature resolution in both cases is better than 1 \r{ }C. The longitudinal spatial resolution is 5 mm, and the lateral spatial resolution for the parallel array is better than 1 mm. [Preview Abstract] |
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