Dielectric and electro-optical properties of some cyanobiphenyl liquid-crystals

A variety of methods have been reviewed for obtaining parallel or perpendicular alignment in liquid-crystal cells. Some of these methods have been selected and developed and were used in polarised spectroscopy, dielectric and electro-optic studies. Also, novel dielectric and electro-optic cells were constructed for use over a range of temperature. Dielectric response of thin layers of E7 and E8 (eutectic mixture liquid-crystals) have been measured in the frequency range (12 Hz-100 kHz) and over a range of temperature (183-337K). Dielectric spectra were also obtained for supercooled E7 and E8 in the Hz and kHz range. When the measuring electric field was parallel to the nematic director, one loss peak (low-frequency relaxation process) was observed for E7 and for E8, that exhibits a Debye-type behaviour in the supercooled systems. When the measuring electric field was perpendicular to the nematic director, two resolved dielectric processes have been observed. The phase transitions, effective molecular polarisabilities, anisotropy of polarisabilities and order parameters of three liquid crystal homologs (5CB, 6CB, and 7CB), 60CB and three eutectic nematic mixtures E7, E8, and E607 were calculated using optical and density data measured at several temperatures. The order parameters calculated using the different methods of Vuks, Neugebauer, Saupe-Maier, and Palffy-Muhoray are nearly the same for the liquid crystals considered in the present study. Also, the interrelationship between density and refractive index and the molecular structure of these liquid crystals were established. Accurate dielectric and dipole results of a range of liquid-crystal forming molecules at several temperatures have reported. The role of the cyano-end group, biphenyl core, and flexible tail in molecular association, were investigated using the dielectric method for some molecules which have a structural relationship to the nematogens. Analysis of the dielectric data for solution of the liquid-crystals indicated a high molecular association, comparable to that observed in the nematic or isotropic phases. Electro-optic Kerr effect were investigated for some alkyl cyanobiphenyls, their nematic mixtures and the eutectic mixture liquid-crystals E7 and E8 in the isotropic phase and solution. The Kerr constant of these liquid crystals found to be very high at the nematic-isotropic transition temperatures as the molecules are expected to be highly ordered close to phase transition temperatures. Dynamic Kerr effect behaviour and transient molecular reorientation were also observed in thin layers of some alkyl cyanobiphenyls. Dichroic ratio R and order parameters of solutions containing some azo and anthraquinone dyes in the nematic solvent (E7 and E8), were investigated by the measurement of the intensity of the absorption bands in the visible region of parallel aligned samples. The effective factors on the dichroic ratio of the dyes dissolved in the nematic solvents were determined and discussed

Liquid -Liquid Equilibrium of (Methylcyclohexane + Methanol + Ethyl Benzene): Experimental Data and UNIQUAC Model

ABSTRACT: INTRODUCTION The precise liquid-liquid equilibria (LLE) data is necessary to rational design of many chemical processes and optimize extraction processes. Many researchers have investigated various kinds of multi-component systems in order to understand and provide further information about the phase behavior and the thermodynamic properties of such systems In order to be able to predict LLE in multi-component systems, we need an adequate equilibrium model. Several LLE systems can be correlated with the solution model of the UNIQUA

Spatiotemporal Distribution of PM10 and PM2.5 within and Around The City of Arak, Iran: Effect of Natural Sources

In the present study, the concentrations of PM10 and PM2.5 were measured within and around the city of Arak from March 2016 through March 2017. The measurements were done every 12 days by means of TSI DustTrak sampler containing specific heads for PM10 and PM2.5. The sampling points included eight stations within the city as well as two stations around the city. The average (±SD) values of 108.56 ±55.56 and 42.58 ±15.88µg/m3 were obtained for daily concentrations of PM10 and PM2.5, respectively. PM10 showed the maximum concentrations during summer (144.47µg/m3) followed by spring (109.44 µg/m3), autumn (100.92µg/m3), and winter (77.12µg/m3). On the other hand, the highest values of PM2.5 was observed during winter (44.13 µg/m3) followed by autumn (42.74µg/m3), summer (37.58µg/m3) and spring (33.77 µg/m3). The correlation between PM10 and PM2.5 was highest in winter (R2=0.9288) followed by spring (R2=0.6728), summer (R2=0.6713), and autumn (R2=0.5592). It was concluded that more than 57 and 19% of the PM2.5 and PM10 samples exceeded the Iranian national ambient air quality standards, respectively

Pollution Potential of General Dentistry Offices in Terms of Wastewater and Solid Waste: A Case Study in the City of Arak, Iran

Dental wastewater and solid waste are one of the most important sources of environmental pollution. The objective of the present study was to evaluate the quality of wastewater and solid waste produced in the general dentistry offices in the city of Arak, Iran. A total number of 30 samples of wastewater and 30 samples of solid waste were taken from 30 general dentistry offices. The samples of wastewater were analyzed for metals and other parameters such as BOD, COD, and TSS. The samples of solid wastes were manually separated into 66 components and 4 categories and then weighted. The mean concentrations of Zn, Cu, Hg, Fe, B, Ba, Sn, Ag, Pb, Al, Mn, Cr, and Co were 3950.09, 2578.59, 1247.28, 1060.21, 538.36, 493.21, 300.91, 156.56, 108.32, 107.37, 91.11, 66.00, and 6.48µg L-1, respectively. The mean generation of dental solid waste in each general dentistry office was 670.22g day-1. Potential infectious waste, domestic-type waste, chemical & pharmaceutical waste, and toxic waste constituted 51.52%, 35.30%, 11.11% and 2.07%, of the total waste generated, respectively. Due to the high levels of some metals in the samples, the wastewater should be treated before discharging into the public sewer

Liquid Phase Equilibria of Aqueous Mixtures of Carboxylic Acids (C₁–C₄) with Ethylbenzene: Thermodynamic and Mathematical Modeling

Liquid–liquid equilibrium (LLE) data were experimentally determined and correlated for the aqueous solutions of a series of carboxylic acids (i.e., formic, acetic, propionic, and butyric acids) with ethylbenzene at a temperature of 298.15 K and <i>p</i> = 101.32 kPa. The ternary mixtures containing of the acids exhibit type-1 LLE behavior. The quality of the observed tie-lines was checked using the Othmer–Tobias equation. The correlations were carried out using the thermodynamic and statistical modeling. The activity coefficient models of UNIQUAC and NRTL were applied to fit the tie lines and values of the binary interaction parameters between each pair of components were obtained. The correlation of the tie lines was also carried out by a GMDH type-NN, which are in agreement with those obtained experimentally. In this work, experimental distribution coefficients and separation factors were estimated. Moreover, the Kamlet–Taft LSER model was employed to correlate these quantities and was interpreted in terms of intermolecular interactions

Quantity & quality analysis and associated management practices of solid waste generated in the general dentistry offices in the city of Arak, 2015

Abstract Background: As dental solid waste are among the most important environmental pollutants due to its high contents of toxic and hazardous agents, suitable treatment and management of it are of great importance. The objective of this study was to quantity & quality analyses of dental solid waste and associated management practices in the general dentistry offices in the city of Arak. Materials and Methods: 15 samples of solid waste were taken from the 5 selected general dentistry offices, classified into 66 components and 4 fractions, and then the quantity & quality characteristics were evaluated. Management practices of the solid waste were also investigated by using a questionnaire. Results: According to the results, per capita and the average generation rate of each dentistry office were 66.71 g/day-patient and 1340.45 g/day, respectively. Potential infectious, domestic-type, chemical & pharmaceutical, and toxic wastes consisted of 54.25%, 35.14%, 8.19%, and 2.14% of the waste generated, respectively. 10 components including latex gloves, nylon & plastic, saliva & blood-contaminated kleenex, paper & cardboard, used ampoules, saliva ejector tubes, gypsum, food waste, saliva & blood-contaminated dental rolls, and nylon gloves were responsible for more than 80% of the total waste generated, respectively. Conclusion: Each fraction of dental solid waste (toxic, chemical & pharmaceutical, potential infectious and domestic-type wastes) should be separately collected and disposed of according to the related criteria