The influence of a bulk twist on the surface memorization in the liquid crystal HOBA

The surface-induced memorization of a smectic C liquid crystal texture in the temperature range of the nematic phase of 4- n -heptyloxybenzoic acid oriented by obliquely evaporated SiO on ITO was removed by imposing a bulk twist (Prevention of surface memorization was not observed when we used a simple ITO coating as the orienting surface.) A twist angle value ( Ωc ≈70°) above which the surface memorization is prevented was found. Using microtextural polarization analysis of the smectic C texture, a qualitative explanation of the phenomenon is suggested. The conditions for preventing the surface memorization were deduced in terms of the balance between the surface and bulk torques. These conditions provide surface anchoring breaking, so removing the surface memory effect.     

Surface memory effect in nematics with smectic C short-range order and hydrogen bonded molecules

A surface memory effect (SME) is found in the dimerized nematic with short range smectic C order of 4-n-octyloxybenzoic acid (OOBA) in a cell whose walls have been covered with an obliquely evaporated SiO or ITO layer. The recording and erasure processes are discussed and erasure in the nematic phase is realized. A mechanism for the surface memorization is presented which takes into account the specific character of dimerized nematics preceding cooling into a smectic C phase.     

Ti:LiNbO3 optical waveguides

Various experiments on Ti diffused optical waveguides in LiNbO₃ have been carried out in order to determine precisely the character of the diffusion process. The required guide parameters and the effective mode indices could be controlled by adjusting only the diffusion time under fixed temperature and film thickness. Therefore the dependence of the guide characteristics on the diffusion time has been investigated in detail. On the basis of the data obtained, a two-stage diffusion model is proposed. In the first stage, the Ti diffusant profile is described by a erfc-function, and the second stage is characterized by a modified Gaussian form.     

Optical beam splitter and focuser in Ti:LiNbO3 planar waveguide

A -type two-electrode system on a Ti diffused optical waveguide in LiNbO₃ has been studied in symmetrical and in asymmetrical operation regimes. In the first case the device acts as a beam splitter or focuser, depending on the polarity of the applied voltage. In the second case the device acts as a scanner. The driving voltage is relatively low. Possible applications are optical communication systems and optical processing of information.     

Total absorption of light by metallic gratings and energy flow distribution

Resonance and non-resonance types of total absorption of light by metallic gratings are discussed in connection with the energy flow distribution. Above the grooves the energy flow distribution for shallow and deep gratings is very similar, while in the grooves curls of flow exist. The resonance type of total absorption is accompanied by a strong compression of flow lines resulting in large electromagnetic enhancement, while for the non-resonance type the flow density near the grooves is not enlarged.     

Confining the Sol-Gel Reaction at the Water/Oil Interface: Creating Compartmentalized Enzymatic Nano-Organelles for Artificial Cells

Living organisms compartmentalize their catalytic reactions in membranes for increased efficiency and selectivity. To mimic the organelles of eukaryotic cells, we develop a mild approach for in situ encapsulating enzymes in aqueous-core silica nanocapsules. In order to confine the sol-gel reaction at the water/oil interface of miniemulsion, we introduce an aminosilane to the silica precursors, which serves as both catalyst and an amphiphilic anchor that electrostatically assembles with negatively charged hydrolyzed alkoxysilanes at the interface. The semi-permeable shell protects enzymes from proteolytic attack, and allows the transport of reactants and products. The enzyme-carrying nanocapsules, as synthetic nano-organelles, are able to perform cascade reactions when enveloped in a polymer vesicle, mimicking the hierarchically compartmentalized reactions in eukaryotic cells. This in situ encapsulation approach provides a versatile platform for the delivery of biomacromolecules.     

Losses in diffused optical waveguides

It has been shown that the attenuation characteristics of TE modes in diffused waveguides are different from those of a conventional slab. A simple semiempirical analysis is performed on the base of a ray-optics picture assuming a parabolic index distribution. Analytical expressions for surface scattering and volume loss are derived. The analysis precisely describes the modal loss behaviour of Ag⁺ ion-exchanged waveguides in glass (new results) and Nb diffused waveguides in LiTaO₃ (data reported by other authors).     

Electrical driving of the surface memorization in dimerized nematics with short range smectic order

Electrical control of the surface memorization of an oriented smectic C texture in the temperature range of dimerized nematics with short range smectic C order (4-n-alkyloxybenzoic acids) is presented. It is demonstrated that by suitable choice of the electric field parameters and surface conditions it is possible to separate the thermal and electrical components of the total erasure activation energy. The significant role of the double charge electric layer in the mechanism of the surface memorization is verified. By the electrical control of the memorization, we have confirmed the electrical part of the modified Rapini-Papoular anchoring energy in the effective surface energy.     

Scanning of the surface polar angle values in liquid crystal cells using the surface memory effect

An optical polarization method for indication of recorded oriented smectic C textures by the process of surface memorization and their accumulation and storage in the nematic temperature range is presented. The recorded accumulated data are identified with the surface conditions-the polar and azimuthal angles. Using strong boundary conditions the assumption is made that the interval for recorded and accumulated textures increases when the anchoring energy is weak.