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Chemical Physics Publications

Instability

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Full-Text Articles in Physics

Surface Wrinkling In Liquid Crystal Elastomers, Aditya Agrawal, Paul Luchette, Peter Palffy-Muhoray, Sibani Lisa Biswal, Walter G. Chapman, Rafael Verduzco Jan 2012

Surface Wrinkling In Liquid Crystal Elastomers, Aditya Agrawal, Paul Luchette, Peter Palffy-Muhoray, Sibani Lisa Biswal, Walter G. Chapman, Rafael Verduzco

Chemical Physics Publications

Structured surfaces give rise to novel and potentially useful properties such as controllable wettability and structural colour. Here, we demonstrate structured surfaces via reversible surface wrinkling in liquid crystal elastomers (LCEs). A thin polymer film deposited on top of a shape-responsive LCE exhibits a reversible, periodic surface wrinkling pattern in response to temperature changes. The orientation of the wrinkles depends on the orientation of the nematic director and the temperature at which the bilayer is prepared, and the wrinkles can be re-oriented in a single sample by heating or cooling the sample above or below the preparation temperature. We show ...


Control Of Viscous Fingering Patterns In A Radial Hele-Shaw Cell, Shuwang Li, John S. Lowengrub, Jake Fontana, Peter Palffy-Muhoray Jan 2009

Control Of Viscous Fingering Patterns In A Radial Hele-Shaw Cell, Shuwang Li, John S. Lowengrub, Jake Fontana, Peter Palffy-Muhoray

Chemical Physics Publications

We study numerically and experimentally the dynamics and control of viscous fingering patterns in a circular Hele-Shaw cell. The nonlocality and nonlinearity of the system, especially interactions among developing fingers, make the emergent pattern difficult to predict and control. By controlling the injection rate of the less viscous fluid, we can precisely suppress the evolving interfacial instabilities. There exist denumerable attractive, self-similarly evolving symmetric, universal shapes. Experiments confirm the feasibility of the control strategy, which is summarized in a morphology diagram.


Monodomain Alignment Of The Smectic-A Liquid Crystalline Phase From The Isotropic Phase, Mitya Reznikov, Bentley Wall, Mark A. Handschy, Philip J. Bos Aug 2008

Monodomain Alignment Of The Smectic-A Liquid Crystalline Phase From The Isotropic Phase, Mitya Reznikov, Bentley Wall, Mark A. Handschy, Philip J. Bos

Chemical Physics Publications

The liquid crystal alignment method described here provides uniform orientation of otherwise difficult-to-align smectic-A liquid crystal materials lacking a nematic phase. The smectic-A phase is grown in the presence of a 10–20 K/mm temperature gradient from an air bubble located within a cell by a photolithographically defined channel in the cell substrates. We obtain uniform layer alignment in millimeter-wide smectic regions at growth rates below about 0.05 μm/s even though there is a tendency for spontaneous nucleation of focal-conic defects at higher growth rates once the width of the smectic-A region exceeds the critical value of ...


Three-Dimensional Imaging Of Dielectric Patterns In Electrohydrodynamic Convection Of A Nematic Liquid Crystal, N. Gheorghiu, Ivan I. Smalyukh, Oleg Lavrentovich, Jim T. Gleeson Oct 2006

Three-Dimensional Imaging Of Dielectric Patterns In Electrohydrodynamic Convection Of A Nematic Liquid Crystal, N. Gheorghiu, Ivan I. Smalyukh, Oleg Lavrentovich, Jim T. Gleeson

Chemical Physics Publications

The transition from surface to bulk normal dielectric rolls in a nematic liquid crystal is imaged by fluorescence confocal polarizing microscopy. The three-dimensional director structure and the liquid flow are scanned in both the layer plane and the transverse plane. Two systems of small-scale convective flow are formed, one at each electrode. Strong anchoring makes director oscillations difficult and charges accumulate by the Carr-Helfrich mechanism. The middle region is a structureless convection where the director oscillates with the frequency of the applied voltage. The small-scale flow eventually fills the cell from one electrode to the other as one system of ...


Unipolar Electro-Optic Effect In A Nematic Cell, V. G. Nazarenko, R. Klouda, Oleg Lavrentovich Jan 1998

Unipolar Electro-Optic Effect In A Nematic Cell, V. G. Nazarenko, R. Klouda, Oleg Lavrentovich

Chemical Physics Publications

We report on a unipolar electro-optic effect in a nematic liquid crystal cell. The cell placed between two polarizers behaves as an "optical diode:" only one polarity of the applied voltage makes the cell transparent. The phenomenon is caused by a double symmetry breaking at the two plates that bound the nematic slab.