Bulletin of the American Physical Society
2012 Annual Meeting of the California-Nevada Section of the APS
Volume 57, Number 13
Friday–Saturday, November 2–3, 2012; San Luis Obispo, California
Session C2: Condensed Matter I: Phase Changes and Liquid Crystals |
Hide Abstracts |
Chair: Sergey Savrasov, University of California, Davis Room: Business 003 0112 |
Friday, November 2, 2012 2:00PM - 2:12PM |
C2.00001: Analysis of an Unusual Liquid Crystal Phase Transition Loni Fuller, Josh Fankhauser, Jonathan Fernsler Liquid crystals are a unique phase of matter that resemble a state between a solid and liquid. Within these properties, liquid crystal molecules have the ability to align and create layers. From this phenomenon, many electro-optical effects can be investigated, such as measuring the tilt angle between molecules at different temperatures and applied electric fields and also measuring the birefringence, which is a unique property of liquid crystals in which the index of refraction of the sample behaves differently along different axes. In order to better understand these electro-optical effects, we designed a more precise protocol of measuring this data. This procedure includes manipulating polarizing filters and measuring the effective light intensities with a camera attached to the microscope. From this, we can more successfully analyze the electroclinic effects of liquid crystal displays. For instance, we analyzed the phase transition of two unusual ``de Vries'' smectic liquid crystals. The phase transition for both materials was consistent with mean field theory near a tricritical phase transition. [Preview Abstract] |
Friday, November 2, 2012 2:12PM - 2:24PM |
C2.00002: Field Control of the Surface Electroclinic Effect in Liquid Crystal Displays I Dana Hipolite, Kara Zappitelli, Karl Saunders Liquid crystals (LCs) are a fascinating class of materials exhibiting a range of phases intermediate between liquid and crystalline. Smectic LCs consist of elongated molecules arranged in a periodic stack (along z) of liquid like layers. In the smectic-A (Sm-A) phase, the average molecular long axis (director) points along z. In the smectic-C (Sm-C) phase, it is tilted relative to z, thus picking out a special direction within the layers. Typically, the Sm-A* to Sm-C* transition will occur as temperature is decreased. In chiral smectics (Sm-*A or Sm-C*) it is possible to induce director titling (i.e. the Sm-C* phase) from the Sm-A* phase via the application of an electric field. This is known as the ``bulk electroclinic effect'' (BECE). Often, e.g. in a LCD, the Sm-A* phase is in contact with a surface. The surface acts as a localized electric field, and induces a local tilt, i.e. a local Sm-C* phase. This ``surface electroclinic effect'' (SECE) leads to a distortion of the smectic layers, which reduces LCD quality. We present a model of the Sm-A*-Sm-C* transition, including both BECE and SECE. Analysis of this model shows that the SECE can be controlled, and even eliminated, by a bulk electric field. [Preview Abstract] |
Friday, November 2, 2012 2:24PM - 2:36PM |
C2.00003: Field Control of the Surface Electroclinic Effect in Liquid Crystal Displays II Kara Zappitelli, Dana Hipolite, Karl Saunders As previously introduced in the presentation by Dana Hipolite, chiral, smectic liquid crystal molecules aligned in layers can be controlled by the application of an electric field, which has a variety of implications for the quality of LCD displays. Both the bulk electroclinic effect (BECE) and surface electroclinic effect (SECE) impact the angle at which the molecules tilt with respect to the director in different areas of the cell. Certain LC's exhibit a continuous Sm-A* to Sm-C* transition, where the angle of the surface and bulk molecules change continually with the electric field. Other LC's exhibit first order transitions where we see jumps in the tilt at different values of the applied electric field for the bulk and surface molecules respectively. The difference in angle of the bulk and surface molecules in both of these situations causes discrepancies in the layer spacing within the LC cell. These discrepancies lead to frustrations within the cell, which can be quantified by the strain (?). These frustrations can be relieved in multiple ways, however the method of relief may lead to negative impacts on the alignment quality of the display itself. [Preview Abstract] |
Friday, November 2, 2012 2:36PM - 2:48PM |
C2.00004: Ordering Quantum Dot Clusters via Nematic Liquid Crystal Defects Andrea Rodarte, R. Pandolfi, L.S. Hirst, S. Ghosh Nematic liquid crystal (LC) materials can be used to create ordered clusters of CdSe/ZnS core/shell quantum dots (QDs) from a homogeneous isotropic dispersion. At the phase transition, the ordered domains of nematic LC expel the majority of dispersed QDs into the isotropic domains. The final LC phase produces a series of QD clusters that are situated at the defect points of the liquid crystal texture. Lower concentrations of QDs are organized in a network throughout the LC matrix that originates from the LC phase transition. Inside the QD clusters the inter-particle distance enables efficient energy transfer from high energy dots to lower energy dots. Because the QD clusters form at defect sites, the location of the clusters can be preselected by seeding the LC cell with defect nucleation points. [Preview Abstract] |
Friday, November 2, 2012 2:48PM - 3:00PM |
C2.00005: New experimental techniques to measure the electroclinic effect in smectic liquid crystals Joshua Fankhauser, Loni Fuller, Jonathan Fernsler Liquid crystals have very unique properties that allow them to alter light in ways that many materials cannot. The smectic liquid crystal phases are fluid, layered arrangements of molecules. We are using a technique to measure both the tilt of molecules away from the direction normal to the layer plane and birefringence as a function of temperature as well as electric field. This is done by projecting light through two polarizers and observing the effect that the sample has on the polarization of the light. The system used to gather data for the sample is a newly automated Matlab program along with a standard temperature logging program. The Matlab program was developed this year to gather accurate intensity readings at a rapid rate and export them for further analyzing. The program is also interfaced with a Labjack so that we will be able to observe and collect data on the unusually large electroclinic effect, the coupling between molecular tilt and applied electric field, in our deVries liquid crystals. [Preview Abstract] |
Friday, November 2, 2012 3:00PM - 3:12PM |
C2.00006: Dielectric Spectroscopy in Liquid Crystals: Zachary Sailer, Crosby Sperling, Jonathan Fernsler We use the technique of dielectric spectroscopy (or impedance spectroscopy) to measure the frequency response of common electronic elements and liquid crystal samples. Using the HP 4192A LF impedance analyzer, an alternating electric field is applied across the sample while the impedance is measured. Applying these fields over a range of frequencies allows us to observe the resonant frequency at which a circuit resists or responds to the field. In a liquid crystal sample, this peak describes the frequency at which the molecules are susceptible to rotating around their tilt cone in the Smectic A and Smectic C phases. This technique also allows us to measure other dielectric properties such as the real and imaginary components of the impedance and the phase angle at which the impedance is projected into the imaginary plane. [Preview Abstract] |
Friday, November 2, 2012 3:12PM - 3:24PM |
C2.00007: X-ray scattering measurements of ionization in shock-compressed deuterium Paul Davis The physical properties of hydrogen at extreme conditions play an important role in our understanding of high-pressure phase transitions, the structure of giant planets and the dynamics of inertial fusion. We report the first microscopic measurements of ionization in dynamically compressed hydrogen. Cryogenic targets were shock-compressed to several times liquid density using a high power laser. An intense burst of 2 keV x-rays was generated using a second laser pulse, probing the dense shock-front. By collecting and spectrally dispersing scattered radiation in both forward and backward directions, we measured collective plasmon oscillations and the Fermi distribution of the electrons freed in the compression process. Combined with velocity interferometry to diagnose shock velocity, we infer a sharp onset of ionization at 3 times compression. These results offer an important new basis for comparison with the many competing theories of high-pressure hydrogen. In particular, comparison with finite temperature quantum molecular dynamics simulations suggests a close relationship between ionization and molecular dissociation. [Preview Abstract] |
Friday, November 2, 2012 3:24PM - 3:36PM |
C2.00008: Liquid Crystal Response to Surface-Plasmon-Induced Electric Fields Zachary Nuno, Linda Hirst, Sayantani Ghosh We demonstrate the effect that localized surface plasmon resonance (LSPR) from gold nanoparticles (AuNPs) has on the director of the nematic liquid crystal 4-Cyano-4'-pentylbiphenyl (5CB). The presence of LSPR of the AuNPs was confirmed using metal enhanced fluorescence of a red dye. Using two light sources, a white light with crossed polarizers to observe the birefringence of the liquid crystal and a 510-550nm light to excite the LSPR, we observe re-orientation of the director of aligned liquid crystal molecules when the AuNPs are excited with light matching the LPSR absorption band. This response is observed to be temperature dependent and only seen to occur within 1 degree Celsius of the phase transition from nematic to isotropic phase. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700