Search results for "Homeotropic alignment"
showing 8 items of 8 documents
Ordering and dewetting in spin-coated films of a liquid crystalline main chain polymer
2006
Abstract The ordering of spin-coated films of a main-chain smectic liquid crystalline polymer with an azobenzene group connected by flexible spacers to a phenyl malonate unit has been studied as a function of film thickness using scanning force microscopy and UV/Vis spectroscopy. Already the as-prepared films are characterized by a significant out-of-plane orientation of the azobenzene groups. Annealing of films thicker than 7 nm results in aggregation and homeotropical alignment of azobenzene groups forming smectic layers parallel to the substrate. An optically isotropic mesophase was found upon annealing in the temperature range of smectic mesophase. Films thinner than the bilayer thickne…
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…
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…
Measurement of elastic forces between iron colloidal particles in a nematic liquid crystal.
2006
The forces that arise between two iron particles in a nematic liquid crystal with a strong homeotropic anchoring were studied. For the first time, the short range repulsive force resulting from the presence of a hedgehog defect between two particles was precisely determined thanks to application of a small magnetic field and observation of the equilibrium position resulting from the balance between the elastic and magnetic forces. Above a given threshold force, the particles stuck together whereas the hedgehog defect was expelled and transformed into a Saturn ring located between the particles. The attractive part of the interparticle force was determined with the same method on the entire …
Orientation and Dynamics of ZnO Nanorod Liquid Crystals in Electric Fields.
2010
ZnO nanorod polymer hybrids (i.e., ZnO nanorods coated with a block copolymer with a short anchor block (dopamine) and a longer solubilizing block of polystyrene (PS)) form liquid crystalline (LC) phases if they are dispersed at high concentration e.g., in a PS oligomer matrix. Due to the high mobility of the low T(g)-matrix the nanorod polymer hybrids show a switching behavior under an applied AC electric field. Hence, the orientation of the nanorod mesogens can be changed from planar (parallel to the substrate) to homeotropic (perpendicular) in full analogy to the switching of low molecular liquid crystals in an electric field. Dielectric measurements show that such a switching is mainly …
Photoswitchable Smectic Liquid-Crystalline Elastomers
2005
We succeeded in the synthesis of azo side chain containing polysioxanes with broad smectic C* and A phases. In these polymers the phase transition temperatures can be shifted reversibly by up to 17°C by irradiation with UV (cis) or VIS (trans) light. Thin films of these polymers in the smectie phase (both on substrates and as free-standing films) orient perfectly in a homeotropic manner. As a consequence, the aze chromophores do no longer absorb during a perpendicular illumination with light (dichroism). It is thus possible to crosslink these films photochemically to prepare photoswitchable smectic LC elastomers.
Freely-Suspended and Transferred Freely-Suspended Films of Polymeric Liquid Crystals
1993
Freely-suspended (FS) liquid-crystal (LC) films of a polymethylsiloxane homo- and a copolymer with different mesogenic side groups have been prepared and investigated. For both substances the preparation of the films succeeded only in the isotropic phase but the higher ordered phases were reached after cooling. The films of the homopolymer have only been obtained with thicknesses estimated to be in the pm-range and with an unusual “Book-Shelf” orientation of the smectic layers. In contrast, the films of the copolymer were thinner and showed a homeotropic orientation of the mesogens in the smectic A phase. Interestingly, this material exhibited a different layer spacing in film and bulk, alt…