Search results for "Tropic"

Reversible Physical Network Stabilized Ferroelectric Liquid Crystals

2001

Acoustic vibrations of anisotropic nanoparticles

2009

Acoustic vibrations of nanoparticles made of materials with anisotropic elasticity and nanoparticles with non-spherical shapes are theoretically investigated using a homogeneous continuum model. Cubic, hexagonal and tetragonal symmetries of the elasticity are discussed, as are spheroidal, cuboctahedral and truncated cuboctahedral shapes. Tools are described to classify the different vibrations and for example help identify the modes having a significant low-frequency Raman scattering cross-section. Continuous evolutions of the modes starting from those of an isotropic sphere coupled with the determination of the irreducible representation of the branches permit some qualitative statements t…

Isotropic-nematic interface and wetting in suspensions of colloidal platelets.

2006

We study interfacial phenomena in a colloidal dispersion of sterically stabilized gibbsite platelets, exhibiting coexisting isotropic and nematic phases separated by a sharp horizontal interface. The nematic phase wets a vertical glass wall and polarized light micrographs reveal homeotropic surface anchoring both at the free isotropic-nematic interface and at the wall. On the basis of complete wetting of the wall by the nematic phase, as found in our density functional calculations and computer simulations, we analyze the balance between Frank elasticity and surface anchoring near the contact line. Because of weak surface anchoring, the director field in the capillary rise region is uniform…

Towards tunable defect arrangements in smectic liquid crystal shells utilizing the nematic–smectic transition in hybrid-aligned geometries

2012

We produce and investigate liquid crystal shells with hybrid alignment—planar at one boundary, homeotropic at the other—undergoing a transition between the nematic (N) and smectic-A (SmA) phases. The shells display a dynamic sequence of patterns, the details depending on the alignment agents and on the diameter and thickness of the shell. In shells of sufficient diameter we typically find a transient striped texture near the N–SmA transition, stabilising into a pattern of tiled, more or less regularly spaced focal conic domains in the SmA phase. The domain size and spacing decrease with reduced shell thickness. In case of strong homeotropic anchoring at one boundary and small shell size, ho…

On the influence of orientation upon the mechanical behavior of oakwood in a general state of stress

1995

Influence of orientation upon the mechanical behavior of oakwood has been studied. The approach within anisotropic medias mechanics supposes oakwood orthotropic with three orthogonal symmetry axes considered to be the privileged directions that occur during the growth of oaktree. Experimental tests consisted in compression tests under confining pressure realized on cylindric samples of oakwood chopped in 18 privileged directions. Although well known in solid mechanics, our approach is original in mechanics and rheology of wood. The obtained results disclosed an influence of the confining pressure upon the mechanical behavior of oakwood and its anisotropy including different types of anisotr…

Mechanical behavior of a sandwich with corrugated GRP core: numerical modeling and experimental validation

2014

In this work the mechanical behaviour of a core reinforced composite sandwich structure is studied. The sandwich employs a Glass Reinforced Polymer (GRP) orthotropic material for both the two external skins and the inner core web. In particular, the core is designed in order to cooperate with the GRP skins in membrane and flexural properties by means of the addition of a corrugated laminate into the foam core. An analytical model has been developed to replace a unit cell of this structure with an orthotropic equivalent thick plate that reproduces the in plane and out of plane behaviour of the original geometry. Different validation procedures have been implemented to verify the quality of t…

Numerical investigation of the mechanical properties of a novel hybrid polymer composite reinforced with graphene and MXene nanosheets

2020

Abstract This paper presents a numerical investigation of the elastic properties of a novel hybrid polymer composite reinforced with graphene and MXene nanosheets. A finite element computational model was developed to analyze the mechanical properties of a new polymer hybrid composite reinforced with MXene and graphene taking into account the properties of the 2D nanosheets, different aspect ratios, placement options and volume fractions of nanoreinforcements, as well as the interaction effects between the nanofillers and the surrounding polymer matrix. Using the developed numerical model, the influences of the interface layer properties, MXene and graphene aspect ratio, alignment and volum…

Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers.

2016

Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). Here, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau-de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. V…

Thalassiosira pseudonana diatom as biotemplate to produce a macroporous ordered carbon-rich material

2008

Abstract Ordered macroporous–mesoporous carbonaceous materials were produced as a direct replica of the Thalassiosira pseudonana diatom by infiltration of the skeleton with furfuryl alcohol. The final carbon-rich material preserves the macropores of the diatom acting as bio-template and new hierarchical macro–mesopores appears as the silica is eliminated through chemical etching. The final solid can be described as an organized array of carbon macrotubes. In order to understand the progressive silica etching and the subsequent effect on the final carbon material, different etching reagents have been used. Moreover, the similar pore topology of T. pseudonana and the well known MCM-41 mesopor…

Broadband Terahertz Probes of Anisotropic Magnetoresistance Disentangle Extrinsic and Intrinsic Contributions

2021

Anisotropic magnetoresistance (AMR) is a ubiquitous and versatile probe of magnetic order in contemporary spintronics research. Its origins are usually ascribed to extrinsic effects (i.e. spin-dependent electron scattering), whereas intrinsic (i.e. scattering-independent) contributions are neglected. Here, we measure AMR of polycrystalline thin films of the standard ferromagnets Co, Ni, Ni81Fe19 and Ni50Fe50 over the frequency range from DC to 28 THz. The large bandwidth covers the regimes of both diffusive and ballistic intraband electron transport and, thus, allows us to separate extrinsic and intrinsic AMR components. Analysis of the THz response based on Boltzmann transport theory revea…