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Full-Text Articles in Physics
Measurement Of The Temperature Dependence Of Radiation Induced Conductivity In Polymeric Dielectrics, Jodie Corbridge Gillespie
Measurement Of The Temperature Dependence Of Radiation Induced Conductivity In Polymeric Dielectrics, Jodie Corbridge Gillespie
Jodie Corbridge Gillespie
This study measures Radiation Induced Conductivity (RIC) in five insulating polymeric materials over temperatures ranging from ~110 K to ~350 K: polyimide (PI or Kapton HNTM and Kapton ETM), polytetraflouroethylene (PTFE or TeflonTM), ethylene-tetraflouroethylene (ETFE or TefzelTM), and Low Density Polyethylene (LDPE). RIC occurs when incident ionizing radiation deposits energy and excites electrons into the conduction band of insulators. Conductivity was measured when a voltage was applied across vacuum-baked, thin film polymer samples in a parallel plate geometry. RIC was calculated as the difference in sample conductivity under no incident radiation and under an incident ~4 MeV electron beam at …
Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli
Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli
Antal Jakli
We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial …
Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli
Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli
Antal Jakli
We have found that bent-core liquid crystalline materials show exceptionally large intrinsic flow birefringence in their isotropic liquid phase. This effect is more than 100 times larger than typical values measured for low molecular weight liquid crystals. The specific flow birefringence (i.e., normalized by the flow viscosity) is an order of magnitude larger than in both side-chain polymeric as well as low molecular weight liquid crystals. We propose that this large enhancement for bent-core compounds may be attributed to nanoscale smecticlike clusters that persist above the nematic-isotropic transition temperature, and shear align under shear flow; however, this mechanism has not …
Length Scales Of Interactions In Magnetic, Dielectric, And Mechanical Nanocomposites, Ralph Skomski, Balamurugan Balamurugan, Eva Schubert, Axel Enders, David J. Sellmyer
Length Scales Of Interactions In Magnetic, Dielectric, And Mechanical Nanocomposites, Ralph Skomski, Balamurugan Balamurugan, Eva Schubert, Axel Enders, David J. Sellmyer
Axel Enders
It is investigated how figures of merits of nanocomposites are affected by structural and interaction length scales, Aside from macroscopic effects without characteristic lengths scales and atomic-scale quantum-mechanical interactions there are nanoscale interactions that reflect a competition between different energy contributions. We consider three systems, namely dielectric media, carbon-black reinforced rubbers and magnetic composites. In all cases, it is relatively easy to determine effective materials constants, which do not involve specific length scales. Nucleation and breakdown phenomena tend to occur on a nanoscale and yield a logarithmic dependence of figures of merit on the macroscopic system size. Essential system-specific differences …
Shape Selection Of Twist-Nematic-Elastomer Ribbons, Yoshiki Sawa, Fangfu Ye, Kenji Urayama, Toshikazu Takigawa, Vianney Gimenez-Pinto, Robin Selinger, Jonathan Selinger
Shape Selection Of Twist-Nematic-Elastomer Ribbons, Yoshiki Sawa, Fangfu Ye, Kenji Urayama, Toshikazu Takigawa, Vianney Gimenez-Pinto, Robin Selinger, Jonathan Selinger
Robin Selinger
How microscopic chirality is reflected in macroscopic scale to form various chiral shapes, such as straight helicoids and spiral ribbons, and how the degree of macroscopic chirality can be controlled are a focus of studies on the shape formation of many biomaterials and supramolecular systems. This article investigates both experimentally and theoretically how the chiral arrangement of liquid crystal mesogens in twist-nematic-elastomer films induces the formation of helicoids and spiral ribbons because of the coupling between the liquid crystalline order and the elasticity. It is also shown that the pitch of the formed ribbons can be tuned by temperature variation. …
Director Dynamics In Liquid-Crystal Physical Gels, Rafael Verduzco, Neal R. Scruggs, Samuel Sprunt, Peter Palffy-Muhoray, Julia A. Kornfield
Director Dynamics In Liquid-Crystal Physical Gels, Rafael Verduzco, Neal R. Scruggs, Samuel Sprunt, Peter Palffy-Muhoray, Julia A. Kornfield
Peter Palffy-Muhoray
Nematic liquid- crystal (LC) elastomers and gels have a rubbery polymer network coupled to the nematic director. While LC elastomers show a single, non- hydrodynamic relaxation mode, dynamic light- scattering studies of self- assembled liquid- crystal gels reveal orientational fluctuations that relax over a broad time scale. At short times, the relaxation dynamics exhibit hydrodynamic behavior. In contrast, the relaxation dynamics at long times are non-hydrodynamic, highly anisotropic, and increase in amplitude at small scattering angles. We argue that the slower dynamics arise from coupling between the director and the physically associated network, which prevents director orientational fluctuations from decaying …
Three-Dimensional Dye Distribution In Photo-Oriented Liquid-Crystal Alignment Layers, S. Bardon, D. Coleman, N. A. Clark, T. Kosa, H. Yuan, Peter Palffy-Muhoray
Three-Dimensional Dye Distribution In Photo-Oriented Liquid-Crystal Alignment Layers, S. Bardon, D. Coleman, N. A. Clark, T. Kosa, H. Yuan, Peter Palffy-Muhoray
Peter Palffy-Muhoray
The three-dimensional optical anisotropy of photo-buffed dye-doped polymer films and the resulting orientation imparted to a liquid crystal in contact are probed using total internal reflection. Although the linearly polarized writing light generates a uniaxial distribution of dye molecules, the polymer films are biaxial, a result of symmetry breaking by the film surface.
Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich
Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich
Oleg Lavrentovich
It is shown experimentally that crossing and intercommutation of disclinations in a bounded nematic cell depend on surface orientation of the director and the relative strength of disclinations. Lines of opposite strength switch the pinned ends between the bounding plates and vanish independently of each other if the surface orientation is tangential. In contrast, tilted surface orientation preserves the stability of lines.
Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck
Nonequilibrium Processes In Polymers Undergoing Interchange Reactions. Part 2: Reaction-Diffusion Processes, Alejandro Garcia, J. Pojman, D. Kondepudi, C. Van De Broeck
Alejandro Garcia
A reactiodffusion system of polymers undergoing interchange reactions is studied. The equation that describes the dynamics of the system is similar to the Boltzmann equation for a gas of hard spheres. We consider a one-dimensionsl system in which the average length and the concentrations at the boundaries are fixed. The resulting steady states are obtained analytically and with numerical integration of equations obtained by using a local equilibrium approximation. Monte Carlo simulations of experimentally realizable conditions were performed and compared. The results reveal a nonlinear distribution of molecular concentration and mass. The entropy of the polymer distributions is calculated as …