1,348 research outputs found
Front Propagation at the Nematic-Isotropic Transition Temperature
We study the gradient flow model for the Landau--de Gennes energy functional for nematic liquid crystals at the nematic-isotropic transition temperature on prototype geometries. We study the dynamic model on a three-dimensional droplet and on a disc with Dirichlet boundary conditions and different types of initial conditions. In the case of a droplet with radial boundary conditions, a large class of physically relevant initial conditions generate dynamic solutions with a well-defined nematic-isotropic interface which propagates according to mean curvature for small times. On a disc, we make a distinction between “planar” and “nonplanar” initial conditions, and “minimal” and “nonminimal” Dirichlet boundary conditions. Planar initial conditions generate solutions with an isotropic core for all times, whereas nonplanar initial conditions generate solutions which escape into the third dimension. Nonminimal boundary conditions generate solutions with boundary layers, and these solutions can either have a largely ordered interior profile or an almost entirely disordered isotropic interior profile. Our examples suggest that while critical points of the Landau--de Gennes energy typically have highly localized disordered-ordered interfaces, the transient dynamics exhibits observable interfaces of potential experimental relevance
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Thermal-Expansion and Fracture Toughness Properties ofParts made from Liquid Crystal Stereolithography Resins
Liquid crystal (LC) resins are a new kind ofstereolithography material that can produce
parts with structured or ordered morphologies instead ofthe amorphous morphologies that result
from standard resins. The LC molecules can be aligned before cure resulting in an anisotropic
crosslinked network when the laser induced polymerization "locks-in" the alignment. Previous
papers have explored liquid crystal orientation dynamics [1], the effects of orientation on viscoelastic and mechanical properties [2,3], and the processing ofLC resins by stereolithography [4].
This paper considers the effects ofmorphology on fracture toughness and thermal-expansion
properties. Both toughness and thermal-stability continue to be important issues for
stereolithography parts. The use ofLC resins may provide a way to significantly improve
performance in both ofthese areas, and in addition result in parts with high upper use .
temperatures.Mechanical Engineerin
Deposition And Drying Dynamics Of Liquid Crystal Droplets
Drop drying and deposition phenomena reveal a rich interplay of fundamental science and engineering, give rise to fascinating everyday effects (coffee rings), and influence technologies ranging from printing to genotyping. Here we investigate evaporation dynamics, morphology, and deposition patterns of drying lyotropic chromonic liquid crystal droplets. These drops differ from typical evaporating colloidal drops primarily due to their concentration-dependent isotropic, nematic, and columnar phases. Phase separation occurs during evaporation, and in the process creates surface tension gradients and significant density and viscosity variation within the droplet. As a result, the drying multiphase drops exhibit different convective currents, drop morphologies, and deposition patterns (coffee-rings)
Confinement Effects on the Crystalline Features of Poly(9,9-dioctylfluorene)
Typical device architectures in polymer-based optoelectronic devices, such as
field effect transistors organic light emitting diodes and photovoltaic cells
include sub-100 nm semiconducting polymer thin-film active layers, whose
microstructure is likely to be subject to finite-size effects. The aim of this
study was to investigate effect of the two-dimensional spatial confinement on
the internal structure of the semiconducting polymer poly(9,9-dioctylfluorene)
(PFO). PFO melts were confined inside the cylindrical nanopores of anodic
aluminium oxide (AAO) templates and crystallized via two crystallization
strategies, namely, in the presence or in the absence of a surface bulk
reservoir located at the template surface. We show that highly textured
semiconducting nanowires with tuneable crystal orientation can be thus
produced. Moreover, our results indicate that employing the appropriate
crystallization conditions extended-chain crystals can be formed in
confinement. The results presented here demonstrate the simple fabrication and
crystal engineering of ordered arrays of PFO nanowires; a system with potential
applications in devices where anisotropic optical properties are required, such
as polarized electroluminescence, waveguiding, optical switching, lasing, etc
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