Atomically Resolved Images Of Bismuth-Films On Mica With An Atomic Force Microscope,
2014
University of Akron Main Campus
Atomically Resolved Images Of Bismuth-Films On Mica With An Atomic Force Microscope, A. Weisenhorn, P. Henriksen, H. Chu, R. Ramsier, Darrell Reneker
Darrell Hyson Reneker
Bi(111) films grown on mica substrates and then exposed to air have been imaged with an atomic force microscope in 0.01 M HCl. By exposing the Bi(111) to air, layers of Bi oxide are readily formed, which can be removed by imaging in HCl. The images are atomically resolved and show two types of structure: large epitaxial areas of hexagonal structure with a spacing of 7.6 angstrom, and a few smaller regions with a spacing of 4.5 angstrom. The former agrees well with the (square-root 3 x square-root 3) R 30-degrees structure of an overlayer of atomic oxygen atoms adsorbed …
Electrical, Structural, And Chemical Properties Of Semiconducting Metal Oxide Nanofiber Yarns,
2014
University of Akron Main Campus
Electrical, Structural, And Chemical Properties Of Semiconducting Metal Oxide Nanofiber Yarns, A. Lotus, E. Bender, E. Evans, R. Ramsier, Darrell Reneker
Darrell Hyson Reneker
The electrical, structural, and chemical properties of twisted yarns of metal-oxide nanofibers, fabricated using a modified electrospinning technique, are investigated in this report. In particular, synthesized zinc oxide and nickel oxide yarns having diameters in the range of 4-40 mu m and lengths up to 10 cm were characterized, whose constituent nanofibers had average diameters of 60-100 nm. These yarns have one macroscopic dimension for handling while retaining some of the properties of nanofibers. (C) 2008 American Institute of Physics.
Bending Instability Of Electrically Charged Liquid Jets Of Polymer Solutions In Electrospinning,
2014
University of Akron Main Campus
Bending Instability Of Electrically Charged Liquid Jets Of Polymer Solutions In Electrospinning, Darrell Hyson Reneker, Alexander L. Yarin, Hao Fong, Sureeporn Koombhongse
Darrell Hyson Reneker
Nanofibers of polymers were electrospun by creating an electrically charged jet of polymer solution at a pendent droplet. After the jet flowed away from the droplet in a nearly straight line, it bent into a complex path and other changes in shape occurred, during which electrical forces stretched and thinned it by very large ratios. After the solvent evaporated, birefringent nanofibers were left. In this article the reasons for the instability are analyzed and explained using a mathematical model. The rheological complexity of the polymer solution is included, which allows consideration of viscoelastic jets. It is shown that the longitudinal …
Branching In Electrospinning Of Nanofibers,
2014
University of Akron Main Campus
Branching In Electrospinning Of Nanofibers, A. L. Yarin, W. Kataphinan, Darrell Hyson Reneker
Darrell Hyson Reneker
Electrospinning of polymer nanofibers often begins with a single, straight, elongating, and electrified fluid jet that emanates from a droplet tip when the electric field at the surface is high enough. After some distance an electrically driven bending instability of the elongating jet occurs. For a polymer solution suitable for electrospinning, capillary instability does not cause the jet to become a spray of droplets. Under some conditions, a sequence of secondary jet branches emanates from the primary jet. This paper describes an experiment in which many closely spaced branches along the jet were observed during the electrospinning of a polycaprolactone …
Electrospinning Route For The Fabrication Of P-N Junction Using Nanofiber Yarns,
2014
University of Akron Main Campus
Electrospinning Route For The Fabrication Of P-N Junction Using Nanofiber Yarns, A. F. Lotus, S. Bhargava, E. T. Bender, E. A. Evans, R. D. Ramsier, Darrell Hyson Reneker, G. G. Chase
Darrell Hyson Reneker
Electrospinning is a simple, versatile, and cost effective method for generating nanoscale fibers, wires, and tubes. Nanowires and nanotubes could be important building blocks for nanoscale electronics, optoelectronics, and sensors as they can function as miniaturized devices as well as electrical interconnects. We report on a simple method to fabricate free standing ceramic nanofiber heterostructures, which exhibit rectifying behavior of a p-n junction.
Taylor Cone And Jetting From Liquid Droplets In Electrospinning Of Nanofibers,
2014
University of Akron Main Campus
Taylor Cone And Jetting From Liquid Droplets In Electrospinning Of Nanofibers, Alexander L. Yarin, S Koombhongse, Darrell Hyson Reneker
Darrell Hyson Reneker
Sessile and pendant droplets of polymer solutions acquire stable shapes when they are electrically charged by applying an electrical potential difference between the droplet and a flat plate, if the potential is not too large. These stable shapes result only from equilibrium of the electric forces and surface tension in the cases of inviscid, Newtonian, and viscoelastic liquids. In liquids with a nonrelaxing elastic force, that force also affects the shapes. It is widely assumed that when the critical potential phi (0*) has been reached and any further increase will destroy the equilibrium, the liquid body acquires a conical shape …
On The Rheology Of Filled Polymers,
2014
University of Akron Main Campus
On The Rheology Of Filled Polymers, Arkadii Leonov
Arkady I. Leonov
No abstract provided.
Non-Markovian Brownian Motion In A Viscoelastic Fluid,
2014
University of Akron Main Campus
Non-Markovian Brownian Motion In A Viscoelastic Fluid, V. S. Volkov, Arkadii I. Leonov
Arkady I. Leonov
A theory of non-Markovian translational Brownian motion in a Maxwell fluid is developed. A universal kinetic equation for the joint probability distribution of position, velocity, and acceleration of a Brownian particle is derived directly from the extended dynamic equations for the system. Unlike the extended Fokker-Planck equation which corresponds to Mori-Kubo generalized Langevin equation and provides only with calculations of one-time moments, the universal kinetic equation obtained gives complete statistical description of the process. In particular, an exact generalized Fokker-Planck equation in the velocity space valid for any time instant is derived for the free non-Markovian Brownian motion. It shows …
On A Self-Consistent Molecular Modeling Of Linear Relaxation Phenomena In Polymer Melts And Concentrated-Solutions,
2014
University of Akron Main Campus
On A Self-Consistent Molecular Modeling Of Linear Relaxation Phenomena In Polymer Melts And Concentrated-Solutions, Arkadii Leonov
Arkady I. Leonov
This paper analyzes the linear version of the theory of ''relaxation interactions'' in polymer melts and concentrated polymer solutions proposed by Pokrovskii and Volkov in 1978, and which was subsequently developed later in many of their other publications; In these papers, the Brownian dynamics of a single macromolecule surrounded by other macromolecules was considered on the basis of the bead and spring model, and the environmental macromolecules were assumed to react as a viscoelastic liquid with an unknown relaxation spectrum. The key problem in this approach is the formulation of the self-consistency condition which delivers the equation for the unknown …
On 1d-Instabilities In Simple Shear And Extensional Flows As Predicted By Some Maxwell-Like Constitutive-Equations,
2014
University of Akron Main Campus
On 1d-Instabilities In Simple Shear And Extensional Flows As Predicted By Some Maxwell-Like Constitutive-Equations, Y. Kwon, Arkadii Leonov
Arkady I. Leonov
One-dimensional (1D) instabilities, some of them of new type, were found in simple shear and simple elongation for Giesekus, Leonov, and Larson viscoelastic constitutive equations (CEs) with single relaxation mode. Whereas 1D instabilities in shear flow were found for all three CEs, only the Larson model manifested some ID instabilities (and even nonexistence of solution) in simple extensional flows.
Molecular Engineering Of Side-Chain Liquid Crystalline Polymers By Living Polymerizations,
2014
University of Michigan
Molecular Engineering Of Side-Chain Liquid Crystalline Polymers By Living Polymerizations, Coleen Pugh, Alan L. Kiste
Coleen Pugh
“Living” anionic, cationic, metalloporphyrin and ring-opening metathesis polymerizations have been used to prepare well-defined side-chain liquid crystalline homopolymers, block and graft copolymers and statistical copolymers. This paper analyzes their successes and failures by reviewing the mechanistic aspects and experimental conditions of each type of polymerization, and identifies other classes of mesogenic monomers that could be polymerized in a controlled manner in the future. The emerging structure/property relationships are then identified using well-defined SCLCPs in which only one structural feature is varied while all others remain constant. The thermal transitions of liquid crystalline polymethacrylates, polynorbomenes and poly(viny1 ether)s reach their limiting …
Modification Of Statistical Threading In Two-Component Pseudorotaxane Melts Using The Amphiphilic Approach And Variations In The Confinement Geometry,
2014
University of Akron Main Campus
Modification Of Statistical Threading In Two-Component Pseudorotaxane Melts Using The Amphiphilic Approach And Variations In The Confinement Geometry, Sagar S. Rane, Wayne L. Mattice, Coleen Pugh
Coleen Pugh
Recently we described a coarse-grained model of poly(ethylene oxide) and then employed that model to study the amount of spontaneous threading of cyclic molecules by linear chains in the melt [C. A. Helfer, G. Xu, W. L. Mattice, and C. Pugh, Macromolecules 36, 10071 (2003)]. Since the amount of statistical threading at equilibrium is small, there is interest in identifying physical changes in the system that will increase the threading. We now use that coarse-grained model to investigate the effect on threading of various hypothetical (but feasible) modifications to the two-component system of macrocycles and linear chains in the melt, …
Growth Dynamics Of Isotactic Polypropylene Single Crystals During Isothermal Crystallization From A Miscible Polymeric Solvent,
2014
University of Akron Main Campus
Growth Dynamics Of Isotactic Polypropylene Single Crystals During Isothermal Crystallization From A Miscible Polymeric Solvent, Rujul Mehta, Wirunya Keawwattana, Thein Kyu
Thein Kyu
The present article presents a spatiotemporal growth of isotactic polypropylene (iPP) single crystals, melt crystallized from a polymeric solvent, i.e., poly (ethylene octene) copolymer that is known to be miscible with iPP. Optical and atomic force microscopic investigations reveal that the melt grown single crystals of iPP develop in the form of two parallel rows of crystal lamellae, but these crystals merge at the tips. To elucidate the mechanism of these emerging parallel rows of iPP crystals, a phase field model pertaining to solidification phenomena has been employed that involves a nonconserved crystal order parameter and a chain-tilting angle. This …
Phase-Field Modeling On Morphological Landscape Of Isotactic Polystyrene Single Crystals,
2014
University of Akron Main Campus
Phase-Field Modeling On Morphological Landscape Of Isotactic Polystyrene Single Crystals, Haijun Xu, Rushikesh Matkar, Thein Kyu
Thein Kyu
Spatio-temporal growth of isotactic polystyrene single crystals during isothermal crystallization has been investigated theoretically based on the phase field model by solving temporal evolution of a nonconserved phase order parameter coupled with a heat conduction equation. In the description of the total free energy, an asymmetric double-well local free energy density has been adopted to represent the metastable melt and the stable solid crystal. Unlike the small molecule systems, polymer crystallization rarely reaches thermodynamic equilibrium; most polymer crystals are kinetically stabilized in some metastable states. To capture various metastable polymer crystals, the phase field crystal order parameter at the solidification …
Phase Equilibria Of A Nematic And Smectic-A Mixture,
2014
University of Akron Main Campus
Phase Equilibria Of A Nematic And Smectic-A Mixture, Hao-Wen Chiu, Thein Kyu
Thein Kyu
A phase diagram of a mixture consisting of nematic and smectic liquid crystals has been calculated self-consistently by combining Flory-Huggins (FH) theory for isotropic mixing and Maier-Saupe-McMillan (MSM) theory for smectic-A ordering. However, the MSM theory can be deduced to the original Maier-Saupe (MS) theory for nematic ordering. To describe the phase transitions involving induced smectic phase and nematic + smectic equilibrium, two nematic and two smectic order parameters for the nematic/smectic mixtures have been coupled through the normalized partition function and the orientation distribution function. Self-consistent numerical solution has been sought in establishing nematic/smectic phase diagrams involving (i) phase …
Breakup Of Spiral And Concentric Ringed Spherulites In Polymer Crystallization,
2014
University of Akron Main Campus
Breakup Of Spiral And Concentric Ringed Spherulites In Polymer Crystallization, Haijun Xu, Hao-Wen Chiu, Yoshifumi Okabe, Thein Kyu
Thein Kyu
Recently, the breakup of spiral and concentric ringed spherulites has been observed experimentally in isothermal crystallization of poly(vinylidene fluoride) in its blends with ethylene vinyl acetate copolymer. To elucidate the phenomenon of spiral breakup in polymer spherulites, a theoretical simulation has been undertaken in the framework of the phase field model of solidification based on time-dependent Ginzburg-Landau equations (TDGL model C) pertaining to the conserved concentration and nonconserved phase field order parameters. The concentration order parameter was described in terms of the Landau-type potential, while the crystal order parameter was expressed in terms of an asymmetric double-well potential to account …
Photopolymerization-Induced Crystallization And Phase Separation In Poly(Ethylene Oxide)/Triacrylate Blends,
2014
University of Akron Main Campus
Photopolymerization-Induced Crystallization And Phase Separation In Poly(Ethylene Oxide)/Triacrylate Blends, Soo Jeoung Park, Thein Kyu
Thein Kyu
The present article describes experimental and theoretical investigations of miscibility and crystallization behavior of blends of poly(ethylene oxide) (PEO) and triacrylate monomer (TA) using differential scanning calorimetry and optical microscopy. The PEO/TA blends manifested a single T(g) varying systematically with composition suggestive of a miscible character in their amorphous states. Moreover, there occurs melting point depression of PEO crystals with increasing TA. A phase diagram was subsequently established that exhibited a solid+liquid coexistence region bound by the liquidus and solidus lines, followed by an upper critical solution temperature (UCST) at a lower temperature. The emerging phase morphology was investigated to …
Kinetics Of Phase Transition In An Anticlinic Liquid Crystal Induced By A Uniform Temperature Field: Growth In One Dimension,
2014
University of Akron Main Campus
Kinetics Of Phase Transition In An Anticlinic Liquid Crystal Induced By A Uniform Temperature Field: Growth In One Dimension, X. Y. Wang, Jian-Feng Li, Eliezer Gurarie, S. Fan, Thein Kyu, S. S. Keast, Charles Rosenblatt
Thein Kyu
It is experimentally demonstrated that a transition from a synclinic to an anticlinic liquid crystal phase occurs via stable domain wall propagation after quenching in a uniform temperature field. Such a one-dimensional growth may be explained in terms of a nonlinear diffusion equation. The experiment provides the first example of free, one-dimensional growth in a system subjected to a pure and uniform temperature field.
Theoretical Investigation On Dynamics Of Photopolymerization-Induced Phase Separation And Morphology Development In Nematic Liquid Crystal/Polymer Mixtures,
2014
University of Akron Main Campus
Theoretical Investigation On Dynamics Of Photopolymerization-Induced Phase Separation And Morphology Development In Nematic Liquid Crystal/Polymer Mixtures, Domasius Nwabunma, Hao-Wen Chiu, Thein Kyu
Thein Kyu
A theoretical investigation of the dynamics of photopolymerization-induced phase separation (PIPS) and morphology development in a nematic liquid crystal (LC) polymer network mixture has been undertaken by incorporating photopolymerization kinetics into the coupled time-dependent Ginzburg-Landau (TDGL-Model C) equations. The simulation on the spatio-temporal evolution of the coupled LC concentration and orientation order parameters reveals that both morphological and scattering patterns for the orientation order parameter initially lag behind those of the concentration order parameter. However, the two fields evolve to the same spatial topologies with the progression of time. The PIPS dynamics is characterized only by the late stage of …
Photopolymerization-Induced Directional Crystal Growth In Reactive Mixtures,
2014
University of Akron Main Campus
Photopolymerization-Induced Directional Crystal Growth In Reactive Mixtures, Soo Jeoung Park, Pankaj Rathi, Thein Kyu
Thein Kyu
Photopolymerization-induced crystallization has been demonstrated in blends of polyethylene oxide-diacrylate at temperatures above the depressed melting temperature of the crystalline component. Upon exposure to ultraviolet irradiation, the melting transition curve moves upward and eventually surpasses the reaction temperature, thereby inducing phase separation as well as crystallization. The present paper demonstrates the occurrence of directionally solidified interface morphologies of polymer crystals subjected to a photointensity gradient. The epitaxially grown seaweed or degenerate structures were observed at the circumference (low-intensity region) while the dense branched spherulites developed at the core high-intensity region.
