85,969 research outputs found
Light-addressable liquid crystal polymer dispersed liquid crystal
Scattering-free liquid crystal polymer-dispersed liquid crystal polymer (LCPDLC)
films are fabricated by combining a room temperature polymerizable liquid crystal (LC)
monomer with a mesogenic photosensitive LC. The morphological and photosensitive
properties of the system are analysed with polarized optical microscopy and high resolution
scanning and transmission electron microscopy. A two-phase morphology comprised of
oriented fibril-like polymeric structures interwoven with nanoscale domains of phase
separated LC exists. The nanoscale of the structures enables an absence of scattering which
allows imaging through the LCPDLC sample without optical distortion. The use of a
mesogenic monomer enables much smaller phase separated domains as compared to nonmesogenic systems. All-optical experiments show that the transmitted intensity, measured
through parallel polarizers, can be modulated by the low power density radiation (31
mW/cm2) of a suitable wavelength (532 nm). The reversible and repeatable transmission
change is due to the photoinduced trans-cis photoisomerization process. The birefringence
variation (0.01) obtained by optically pumping the LCPDLC films allow their use as an alloptical phase modulato
100 GHz electrically tunable planar Bragg grating via nematic liquid crystal overlay towards reconfigurable WDM networks
Novel liquid crystal-based integrated optical devices with >140GHz electrical tuning are presented for application towards reconfigurable wavelength division multiplexing (WDM) networks. Initial results with Bragg wavelength tuning covering five 25GHz WDM channel spacing have been achieved with 170V (peak-to-peak) sinusoidal voltages applied across electro-patterned ITO-covered glass electrodes placed 60µm apart. These prototype devices were fabricated using direct UV grating writing, with an evanescent field coupling into a liquid crystal overlay through an etched window. Electrically controlled liquid crystal birefringence modifies the waveguide effective index, resulting in Bragg wavelength shift. Merck 18523 nematic liquid crystals are used, exhibiting compatible refractive index values to that of silica (no=1.44, ne=1.49 at lambda=1550nm). Homeotropic alignment of the liquid crystal is provided by application of a surfactant layer.The inherent refractive index sensitivity of our etched direct-UV-written structures allows observation of previously unreported liquid crystal surface-behaviour, such as multi-threshold points during variation of the applied field. Continued optimisation based on evanescent field penetration, electrode layout, and surface interaction will allow implementation towards a variety of novel liquid crystal applications and devices. For example, a cascaded architecture of these integrated liquid crystal devices operating at different Bragg wavelengths would pave the way towards true colorless add/drop modules for dense optical networks
The design and investigation of nanocomposites containing dimeric nematogens and liquid crystal gold nanoparticles with plasmonic properties showing a nematic-nematic phase transition (Nᵤ-Nₓ/Ntb)
The construction of liquid crystal compositions consisting of the dimeric liquid crystal, CB_C9_CB (cyanobiphenyl dimer = 1",9"-bis(4-cyanobiphenyl-4'-yl)nonane), and the range of nematic systems is explored. The materials include a laterally functionalized monomer, which was used to construct a phase diagram with CB_C9_CB, as well as one laterally linked dimer liquid crystal material and two liquid crystal gold nanoparticle (LC-Au-NPs) systems. For the Au-NP-LCs, the NP diameters were varied between ~3.3 nm and 10 nm. Stable mixtures that exhibit a nematic-nematic phase transition are reported and were investigated by POM (polarizing optical microscopy), DSC (differential scanning calorimetry) and X-ray diffraction studies
A uniqueness and regularity criterion for Q-tensor models with Neumann boundary conditions
We give a regularity criterion for a -tensor system modeling a nematic
Liquid Crystal, under homogeneous Neumann boundary conditions for the tensor
. Starting of a criterion only imposed on the velocity field two
results are proved; the uniqueness of weak solutions and the global in time
weak regularity for the time derivative .
This paper extends the work done in [F. Guill\'en-Gonz\'alez, M.A.
Rodr\'iguez-Bellido \& M.A. Rojas-Medar, Sufficient conditions for regularity
and uniqueness of a 3D nematic liquid crystal model, Math. Nachr. 282 (2009),
no. 6, 846-867] for a nematic Liquid Crystal model formulated in , where denotes the orientation vector of the liquid crystal
molecules.Comment: 13 page
Electro-optical switching by liquid-crystal controlled metasurfaces
We study the optical response of a metamaterial surface created by a lattice
of split-ring resonators covered with a nematic liquid crystal and demonstrate
millisecond timescale switching between electric and magnetic resonances of the
metasurface. This is achieved due to a high sensitivity of liquid-crystal
molecular reorientation to the symmetry of the metasurface as well as to the
presence of a bias electric field. Our experiments are complemented by
numerical simulations of the liquid-crystal reorientation.Comment: 6 pages, 3 figure
Critical Field Strength in an Electroclinic Liquid Crystal Elastomer
We elucidate the polymer dynamics of a liquid crystal elastomer based on the
time-dependent response of the pendent liquid crystal mesogens. The molecular
tilt and switching time of mesogens are analyzed as a function of temperature
and cross-linking density upon application of an electric field. We observe an
unexpected maximum in the switching time of the liquid crystal mesogens at
intermediate field strength. Analysis of the molecular tilt over multiple time
regimes correlates the maximum response time with a transition to entangled
polymer dynamics at a critical field strength.Comment: 4 pages, 3 figure
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