Interfacial Behavior,Structure, and Thermodynamics of Water in Oil Microemulsion Formation in Relation to the Variation of Surfactant Head Group and Cosurfactant

Interfacial behavior, structural, and thermodynamic parameters in relation to the formation of water-in-oil (w/o) microemulsion (μE) with varied surfactant head groups and cosurfactants have been evaluated through dilution technique at different temperature and [water]/[surfactant] mole ratio. Dodecyltrimethylammonium bromide (DTAB), sodium dodecylsulphate (SDS), and polyoxyethylene sorbitan monolaurate (Tween-20) were used as surfactants and n-butanol and n-pentanol were used as cosurfactants. Distribution of cosurfactants between bulk oil and the interface using fixed amount of surfactant at varied [water]/[surfactant] mole ratio and temperature has been studied to evaluate thermodynamic parameters. Associated structural parameters, such as droplet dimension and aggregation number of surfactant and cosurfactant at the droplet interface, have also been evaluated. Spontaneity of the μE formation followed the order DTAB>SDS>Tween-20 for both butanol and pentanol in the studied range of temperature. Correlations of the results in terms of the evaluated physicochemical parameters have been attempted.     

The Influences of Polymers and Temperature on the Foam Properties of 3‐Dodecylalkoxyl‐2‐hydroxylpropyl Trimethylammonium Chloride

The foam performances of 3‐dodecoxy‐2‐hydroxypropyl trimethylammonium chloride (C₁₂TAC) have been determined in the existence of different relative amount of polymer. The experimental results show that the foaming ability of the mixture systems of the C₁₂TAC/PEG and C₁₂TAC/PVP is stronger than that of the surfactant solutions in the absence of polymer, and with the increase of relative amount of polymer both foaming efficiency and foam stability of the surfactant solutions are evidently enhanced. For the aqueous solution of the surfactant, effect of temperature on foaming properties has also been examined. The results show that both the foaming ability and stability of the foams of the surfactant solutions are highest (or strongest) at 30°C.     

Majolica ware in the New Spain: an evaluation through NAA

The results of a study about Majolica ceramics recovered from three sites located in Mexico City are here presented. The set of 83 samples includes several local ceramic-types dating from the Colonial Period, the nineteenth century and the present day, plus some foreign specimens and clay samples from the Puebla area. Fourteen chemical elements present in the samples were analyzed and measured by means of neutron activation, and statistically the following groups were established: two groups that were presumably manufactured in Mexico City, two from Puebla, one from outside the Mexican boundaries, most probably Sevilla-Triana pottery, plus three more groups from unidentified origins. It was also found out that botijas were both imported and produced domestically. These results are discussed against the relevant literature on known provenance, chronology and manufacture standards of this kind of pottery.     

Analytical-numerical solution for turbulent jet diffusion flames of hydrogen

The hydrogen fuel seems to be a good candidate to replace the energy obtained from some fossil fuels. Therefore this work explains the process of obtaining a two-step reduced chemical kinetic mechanism for the hydrogen combustion. The development of a reduced mechanism consists in eliminating reactions that produce negligible influence on the combustion process. Moreover, for this mechanism, we obtain an analytical-numerical solution for a turbulent jet diffusion flame. To quantify the intermediate species, the mixture fraction is decomposed into three parts, each part directly related to the mass fraction of a species. The governing equations are discretized using the second order finite-difference approach and are integrated in time using the second order simplified three-step Runge-Kutta scheme. Obtained results compare favorably with data in the literature for a 50/50 % volume H ₂?N ₂ jet diffusion flame. The main advantage of this strategy is the decrease of the work needed to solve the system of governing equations, by one order of magnitude for the hydrogen.     

Morphology and electro-optical properties of reverse mode polymer dispersed liquid crystals

We have investigated the morphology and electro-optical properties of reverse mode polymer dispersed liquid crystals as a function of liquid crystal loading. Reverse mode shutters have been obtained by a polymerization-induced phase separation of mixtures, consisting of a liquid crystalline monomer and a non-reactive nematic liquid crystal, placed between rough conductive surfaces. Such surfaces are able to keep the photopolymerizable mixtures homeotropically aligned without the use of any aligning polymer substrate. OFF state transmittances are always larger than 80% and the switching fields decrease if the non-reactive liquid crystal percentage is increased. Both rise and decay times are always lower than 10 ms. The electro-optical properties have been related to the sample morphology and a simple mode is proposed.     

Camphor and nopinone derivatives as new photosensitive chiral dopants

E-Z photoisomerizable chiral dopants are a class of materials that can be used to prepare birefringent optical components with patterned optical properties. Two new photoisomerizable chiral dopants have been synthesized and analysed. The materials were derived from nopinone and camphor. The properties of these compounds were compared with the properties of the methone derivative described in earlier publications. The E-isomers of the nopinone and camphor derivatives had helical twisting powers of 2.7 and 1.7 μm^-1, respectively. This is a factor of about 10 lower than the value obtained for the menthone derivative (-19 μm^-1). Due to the high absorption of the Z-isomers relative to the E-isomers of the nopinone and camphor derivatives, isomerization during 365 nm UV exposure proceeded to a much lesser extent than the isomerization of the menthone derivative. At shorter wavelengths, the absorption of the Z-isomer is much lower than that of the E-isomer and much higher degrees of conversion could be achieved.     

The electro‐optical properties of ‘charged’ PDLCs

The application of high intensity electric fields to polymer dispersed liquid crystal (PDLC) films can induce changes in their electro‐optical properties and morphology. In particular, a quasilinear electro‐optical response to an external electric field can be achieved if an internal built‐in d.c. field is induced. In this work, we show how the liquid crystal/polymer weight ratio influences the electro‐optical response of ‘charged’ PDLCs, i.e. of PDLC films after the application of a high intensity electric field. We observed that a quasilinear electro‐optical response can be achieved in a well determined range of composition. Larger liquid crystal concentrations are unable to maintain the built‐in field, while PDLCs with lower liquid crystal loadings do not allow the onset of a built‐in d.c. field.     

Achiral diacrylate with an anticlinic smectic phase

We present an achiral diacrylate that shows a phase transition from the synclinic smectic C phase (SmC) to the anticlinic smectic C (SmCalt). This last phase has been previously reported only for swallow-tailed or dimeric compounds. Our studies using differential scanning calorimetry, X-ray diffraction, polarizing optical microscopy and broad band dielectric spectroscopy suggest the existence of this mesophase in this bifunctional smectogen.     

Photochromic reverse mode polymer dispersed liquid crystals

Control of light intensity and colour are two of the major features required in the realization of smart windows. We designed a bi‐functional polymer dispersed liquid crystal (PDLC) film in order to satisfy such requirements, i.e. it is able both to modulate the optical transmission, if an external electric field is applied, and to change colour if exposed to sunlight. A monomer/liquid crystal mixture was doped with a small amount of photochromic material and homeotropically aligned by means of rough surfaces. A transparent and pale pink coloured film was achieved after photopolymerization. Such a film changes colour upon exposure for some seconds to sunlight or ultraviolet radiation in a persistent but reversible manner. In addition, the film appears transparent without the application of an electric field (OFF state) and becomes opaque on application of a driving voltage of about 75?V (ON state), and thus the film operates in reverse mode with respect to conventional PDLCs.     

Liquid crystal orientation in elliptic droplets in nematic emulsions

Elliptic droplets of nematic liquid crystal dispersed in a fluid organic monomer were obtained by phase separation from an isotropic mixture consisting of an organic monomer and a nematic liquid crystal contained in a poly(ethylene terephthalate) cell with inner surfaces treated with rubbed polyimide. The elliptic shape is a consequence of the constraint upon droplet growth along the direction perpendicular to the cell surfaces owing to the small thickness. Then, the resulting droplets will have a contact area with the inner surfaces of the cell treated with polyimide, which will impart a planar orientation on the liquid crystal in the droplet. By means of an optical microscope, using a simple pin hole of 5 μ m, we have selected single droplets for a series of samples having different contact areas. By polarized infrared spectroscopy we have also studied the liquid crystal orientation in selected areas of the droplets. We then report the dependence of the order parameter of the liquid crystal on different contact areas with the alignment surface of the cell. The good degree of planar alignment of the liquid crystal in the elliptic droplets allows the use of such a technique for realizing electro-optical films operating in the reverse mode. We report the electro-optical transmission of reverse mode films with different sizes of elliptic droplet.