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Full-Text Articles in Physics

Inelastic Collisions And Anisotropic Aggregation Of Particles In A Nematic Collider Driven By Backflow, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich Jan 2011

Inelastic Collisions And Anisotropic Aggregation Of Particles In A Nematic Collider Driven By Backflow, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We design a nematic collider for controlled out-of-equilibrium anisotropic aggregation of spherical colloidal particles. The nematic surrounding imparts dipolar interactions among the spheres. A bidirectional backflow of the nematic liquid crystal in a periodic electric field forces the spheres to collide with each other. The inelastic collisions are of two types, head to tail and head to head. Head-to-tail collisions of dipoles result in longitudinal aggregation while head-to-head collisions promote aggregation in the transversal direction. The frequency of head-to-head collisions is set by the impact parameter that controls the resulting shape of aggregates, their anisotropy, and fractal dimension.


Polar And Nonpolar Orderings In The Electrically Induced Isotropic-Nematic Phase Transition, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2008

Polar And Nonpolar Orderings In The Electrically Induced Isotropic-Nematic Phase Transition, Mingxia Gu, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

We study the dynamics of the isotropic-nematic phase transition caused by an applied electric field at the time scales of dielectric relaxation. In the classic Landau-Khalatnikov theory of the phase transition dynamics, the nematic (nonpolar) order parameter is an instantaneous function of the applied field. We demonstrate that, when the field is changing faster than the time of dielectric relaxation, the induced polar order dynamics influences the dynamics of the nonpolar order parameter. We develop a model based on the Langevin equation to describe the simultaneous dynamics of both polar and nonpolar order parameters; the model is supported by experiment.


Determination Of Interphase Line Tension In Langmuir Films, Jacob R. Wintersmith, Lu Zhou, Andrew J. Bernoff, J. Adin Mann Jr, Edgar E. Kooijman, Elizabeth K. Mann Jun 2007

Determination Of Interphase Line Tension In Langmuir Films, Jacob R. Wintersmith, Lu Zhou, Andrew J. Bernoff, J. Adin Mann Jr, Edgar E. Kooijman, Elizabeth K. Mann

Biological Sciences Publications

A Langmuir film is a molecularly thin film on the surface of a fluid; we study the evolution of a Langmuir film with two coexisting fluid phases driven by an interphase line tension and damped by the viscous drag of the underlying subfluid. Experimentally, we study a 4′-8-alkyl[1,1′-biphenyl]-4-carbonitrile (8CB) Langmuir film via digitally imaged Brewster angle microscopy in a four-roll mill setup which applies a transient strain and images the response. When a compact domain is stretched by the imposed strain, it first assumes a bola shape with two tear-drop shaped reservoirs connected by a ...


Smectic-A-Filled Birefringent Elements And Fast Switching Twisted Dual-Frequency Nematic Cells Used For Digital Light Deflection, Oleg Pishnyak, Andrii Golovin, Liubov Kreminska, John J. Pouch, Felix A. Miranda, Bruce K. Winker, Oleg Lavrentovich Apr 2006

Smectic-A-Filled Birefringent Elements And Fast Switching Twisted Dual-Frequency Nematic Cells Used For Digital Light Deflection, Oleg Pishnyak, Andrii Golovin, Liubov Kreminska, John J. Pouch, Felix A. Miranda, Bruce K. Winker, Oleg Lavrentovich

Chemical Physics Publications

We describe the application of smectic A (SmA) liquid crystals for beam deflection. SmA materials can be used in digital beam deflectors (DBDs) as fillers for passive birefringent prisms. SmA prisms have high birefringence and can be constructed in a variety of shapes, including single prisms and prismatic blazed gratings of different angles and profiles. We address the challenges of uniform alignment of SmA, such as elimination of focal conic domains. Fast rotation of the incident light polarization in DBDs is achieved by an electrically switched 90-deg twisted nematic (TN) cell.


Topological Defects In Schlieren Textures Of Biaxial And Uniaxial Nematics, C. Chiccoli, I. Feruli, Oleg Lavrentovich, P. Pasini, Sergij V. Shiyanovskii, C. Zannoni Sep 2002

Topological Defects In Schlieren Textures Of Biaxial And Uniaxial Nematics, C. Chiccoli, I. Feruli, Oleg Lavrentovich, P. Pasini, Sergij V. Shiyanovskii, C. Zannoni

Chemical Physics Publications

Monte Carlo and theoretical studies of thin 3D films of biaxial and uniaxial nematics with tangential boundary conditions show distinct differences in structure and evolution of topological defects. In the uniaxial films, defects of strength k=+/-1 are point defects that bear no bulk singularity and disappear by annihilation with each other. In the biaxial films, k=+/-1 defects are true singular bulk disclinations that split into pairs of k=+/-1/2 lines; the latter disappear by annihilation processes of the type +1/2-1/2=0. These observed differences are of relevance for the current debate on the existence of ...


Measurement Of Polar Anchoring Coefficient For Nematic Cell With High Pretilt Angle, Darius Subacius, V. M. Pergamenshchik, Oleg Lavrentovich Jul 1995

Measurement Of Polar Anchoring Coefficient For Nematic Cell With High Pretilt Angle, Darius Subacius, V. M. Pergamenshchik, Oleg Lavrentovich

Chemical Physics Publications

A method to determine the surface anchoring energy of a nematic liquid crystal is proposed. The technique implies the measurements of optical retardation of a nematic cell as a function of a strength and direction of the applied magnetic field. It enables one to get both pretilt angle α and anchoring coefficient W a in the course of the same experiment. As an example, both parameters (α=10.9° and W a =1.5×10−5 J/m2) are measured at the interface between the nematic 5CB and rubbed polyimide film.