Orientational control of liquid crystal molecules via carbon nanotubes and dichroic dye in polymer dispersed liquid crystal

Polymer dispersed liquid crystals (PDLCs) using nematic liquid crystal and photo-curable polymer (NOA 65) were prepared by polymerisation-induced phase separation technique, in equal ratio (1:1) of polymer and liquid crystal (LC). We demonstrate that doping of small amount (0.125%, wt./wt.) of multiwall carbon nanotubes (CNTs) and orange azo dichroic dye in PDLC generously controlled the molecular orientation, dynamics of LC in droplet and size of droplets. The effects of multiwall CNTs and dye on PDLCs were studied in terms of transition temperature, droplet morphology, transmittance characteristic, contrast ratio and response time. The results exhibited that the values of the threshold electric fields were reduced from 8 V/µm (pure PDLC) to 1.18 and 1.72 V/µm, doped with multiwall CNTs and dye, respectively. The CNTs-doped PDLC shows faster switching response as compared with pure PDLC and dye-doped PDLC. However, dye-doped PDLC shows much higher contrast among all PDLC samples. Further, the results also illustrate that the birefringence value of LC in PDLCs was changed with doping of CNTs and dye.     

Physico-chemical Investigation of Mixed Micelle Formation Between Tetradecyltrimethylammonium Bromide and Dodecyltrimethylammonium Chloride in Water and Aqueous Solutions of Sodium Chloride

Conductometric measurements have been employed to gain a detailed insight into the interactions between two cationic surfactants, tetradecyltrimethylammonium bromide (TTAB) and dodecyltrimethylammonium chloride (DTAC), in water and in an aqueous solution of sodium chloride. The experimental data were analyzed according to Rubingh’s model within the framework of the pseudophase separation model. The evaluated values of critical micelle concentration (cmc) were found to be lower than their corresponding cmc ^id values, signifying attractive interactions involving both components in the solutions. The micellar mole fractions (\( X_{1}^{\text{Rub}} \)) of TTAB evaluated by Rubingh’s model were always larger than the ideal values (\( X_{1}^{\text{id}} \)), signifying the higher involvement of TTAB in mixed micelles of TTAB and DTAC. Activity coefficients (\( f_{ 1}^{\text{Rub}} \) and \( f_{ 2}^{\text{Rub}} \)) were always below one in all cases signifying synergism in the mixed micelles. All the outcomes point to synergism and attractive interactions in the mixed systems. Values of excess Gibbs energy were evaluated by employing Rubingh’s model (\( \Delta G_{\text{ex}}^{\text{Rub}} \)) and the \( \Delta G_{\text{ex}}^{\text{Rub}} \) values obtained are negative. The values of \( \Delta H_{\text{m}}^{\text{o}} \) and \( \Delta S_{\text{m}}^{\text{o}} \) reveal that hydrophobic interaction is expected to be the binding force between TTAB and DTAC in aqueous media at lower temperatures, while both hydrophobic interactions as well as exothermic interactions are involved at higher temperatures. The interaction forces between the surfactants were found to be enhanced in the presence of NaCl.     

Facile convergent route to indoloquinolines

A convergent route to indoloquinolines is developed through aldol condensation. This two-step method utilizes commercially available 2-oxoindole and o-nitrobenzaldehyde as starting materials. Chromatography-free method is accomplished for preparing several derivatives of indoloquinolines with desirable aromatic substitutions on indole as well as quinoline ring.     

An inverse problem for a family of two parameters time fractional diffusion equations with nonlocal boundary conditions

The determination of a space‐dependent source term along with the solution for a 1‐dimensional time fractional diffusion equation with nonlocal boundary conditions involving a parameter β>0 is considered. The fractional derivative is generalization of the Riemann‐Liouville and Caputo fractional derivatives usually known as Hilfer fractional derivative. We proved existence and uniqueness results for the solution of the inverse problem while over‐specified datum at 2 different time is given. The over‐specified datum at 2 time allows us to avoid initial condition in terms of fractional integral associated with Hilfer fractional derivative.     

Hydrothermal synthesis of brookite TiO<Subscript>2</Subscript> nanoparticles for dye-sensitized solar cell

We obtained Tannin-4-azobenzoic acid (azo dye) by the conventional method of diazotization and coupling of aromatic amines. The properties of the azo dye were characterized via ultraviolet-visible (UV–vis), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopy. Nanocrystalline titanium dioxide (TiO₂) thin films were deposited by hydrothermal method onto fluorine-doped tin (IV) oxide (FTO)-coated glass substrate at 353 K for 4 h. The as-deposited and annealed films were characterized for structural, morphological, optical, thickness, and wettability properties. The synthesized metal free azo dye was used to sensitize the prepared TiO₂ thin film with thickness of 26 μm. The photoelectrochemical (PEC) performance of TiO₂ sensitized with the azo dye was evaluated in polyiodide (0.1 M KI + 0.01 M I₂ + 0.1 M KCl) electrolyte at 40 mW cm^?2 illumination intensity. The cell yielded a short circuit current of 2.82 mA, open circuit voltage of 314.3 mV, a fill factor of 0.30, and a photovoltaic conversion efficiency value of 0.64%.

Open image in new window

Graphical abstract ?

     

On the nature of PSE approximation

The recently developed method of parabolized stability equations (PSE) offers a fast and efficient way of analyzing the spatial growth of linear and nonlinear (convective) disturbances in shear layers. For incompressible flows, the governing equations may be represented either in primitive variables or by using other formulations obtained by eliminating the pressure gradient (e.g., vorticity-streamfunction formulation). On the other hand, for compressible flows, primitive variables offer a natural and the only choice. We show that primitive-variable formulation is not well-posed due to the ellipticity introduced by the term and the marching solution eventually blows up for a sufficiently small step size. However, it is shown that this difficulty can be overcome if the minimum step size is greater than the inverse of the real part of the streamwise wave number, _r. An alternative is to drop the term, in which case the residual ellipticity is of no consequence for marching computations with much smaller step sizes. However, the ellipticity cannot be completely removed. Results obtained with streamfunction and vorticity-velocity formulations also show that the numerical difficulties arise for a sufficiently small marching step size. This step-size restriction can be overcome by dropping thed/dx term from the governing equations. The effect of this term on solution accuracy is negligible for Blasius flow but not so for rotating-disk flow.This work was performed under AFOSR contract F49620-91-C-0014.     

Calculation of the length of the shock-boundary layer interaction zone

An analytic relation for determining the length of the shock-laminar or turbulent boundary layer interaction zone is obtained on the basis of an analysis of the boundary layer separation criterion. It is shown that as the Mach number of the flow increases, the interaction length decreases, and that with increase in the Reynolds number it behaves nonmonotonically: in the laminar region it increases, while on transition to the turbulent regime it falls sharply and then varies along a curve with a maximum. The results of the calculations are in satisfactory agreement with the existing experimental data.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 180–183, March–April, 1987.     

Semiempirical method of calculating overexpanded turbulent separated flow in a conical laval nozzle

A mathematical model of separated nozzle flow is developed. The model takes into account the effect of the boundary layer and the pressure variation over the entire separation zone inside the nozzle. The effect of the geometric and gas dynamic factors on the separated flow pattern is investigated numerically.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 60–66, November–December, 1988.