Security devices based on liquid crystals doped with a colour dye

Liquid crystal properties make them useful for the development of security devices in applications of authentication and detection of fakes. Induced orientation of liquid crystal molecules and birefringence are the two main properties used in security devices.     

Theoretical study of the vibrational frequencies of carbon disulfide

A benchmark comparison for different computational methods and basis sets has been presented. In this study, five computational methods (Hartree–Fock (HF), MP2, B3LYP, MPW1MP91, and PBE1PBE) along with 18 basis sets have been applied to optimize the geometry of carbon disulfide (CS₂), and further calculate the vibrational frequencies of the optimized geometries. The differences between the calculated frequencies and corresponding experimental data are used to evaluate the efficiency of each combination of computational method and basis set. The comparison of frequency difference indicates that B3LYP generally gives the best prediction of frequencies for CS₂, whereas the other two density functional theory (DFT) methods, i.e., MPW1PW91 and PBE1PBE, often give parallel results. Although MP2 predicts the frequencies with accuracy almost as good as those from DFT methods, in a particular case, HF calculation outperforms MP2 as well as MPW1PW91 and PBE1PBE for prediction of the frequency of asymmetrical stretching for CS₂. © 2013 Wiley Periodicals, Inc.     

Polyterephthalates made from Ethylene glycol, 1,4‐cyclohexanedimethanol,and isosorbide

Three series of terephthalate polyesters (copolyesters and terpolyesters) containing 70, 80, and 90 mol % of ethylene glycol respectively, 1,4‐cyclohexanedimethanol (CHDM) and isosorbide in varying ratios, were synthesized by melt polycondensation. It was found that only ～75 mol % of the feeding isosorbide was incorporated in the resulting polyesters and that their content in diethylene glycol oscillated between 2 and 4 mol %. The polyesters had weight‐average molecular weights in the 25,000–33,000 g mol^?1 range and polydispersities between 2 and 2.5. The combined ¹H and ¹³C NMR analysis revealed that the microstructure of all these polyesters was at random. They showed good thermal stability with decomposition temperatures above 400 °C. Their glass‐transition temperatures were observed to increase with the content in cyclic diols, this effect being more pronounced when isosorbide was the replacing comonomer. Only the series containing 90 mol % of ethylene terephthalate units was able to crystallize upon cooling from the melt. Compared isothermal crystallizations revealed that isosorbide was more effective than CHDM in repressing the crystallizability of PET. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Self‐Assembled Monolayers of Cucurbit[6]uril on a Gold Electrode for 4,4′‐Oxydianiline Determination. Analytical Application

Self‐assembled monolayers of cucurbit[6]uril (CB[6]) on a gold electrode have been used for 4,4′‐oxydialine (ODA) analysis. The formation of the supramolecular complex between ODA and CB[6] was used for the molecular selection and the electroanalytical determination of this analyte. In addition to this, all the parameters affecting the modification of the gold electrode and the determination of 4,4′‐oxydianiline were optimized by square wave voltammetry. Upon the electrode modification, pentanethiol was employed to fill up the exposed surface between CB[6] molecules. The calculated detection and determination limits were 0.06 µg mL^?1 and 0.19 µg mL^?1, respectively, with good accuracy and precision as shown by the calculated values for the relative error and relative standard deviation (E_r=0.1 % and RDS=2.9 %; n=10 ). Moreover, the developed methodology was successfully applied to the 4,4′‐oxydialine determination in real wastewaters and shoe‐dyeing samples.     

A metal-free approach to access ketones,amides, and nitriles employing TBAI/TBHP oxidative system in water

Hydrocarbons, benzylamines, and heteroaromatic-bearing amines have been efficiently employed as substrates in allylic and benzylic oxidations via C(sp3)–H bond activation by TBAI/TBHP in water. This operationally simple method allows access to ketones, nitriles, and amides in moderate to high yields and a regio- and chemoselective late-stage functionalization.     

Interlaboratory Study of Digital Volume Correlation Error Due to X-Ray Computed Tomography Equipment and Scan Parameters: an Update from the DVC Challenge

Experimental Mechanics - The quality of Digital Volume Correlation (DVC) full-field displacement measurements depends directly on the characteristics of the X-ray Computed Tomography (XCT)...     

Poly(butylene terephthalate‐co‐5‐tert‐butyl isophthalate) copolyesters: Synthesis,characterization, and properties

A series of poly(butylene terephthalate) copolyesters containing 5‐tert‐butyl isophthalate units up to 50 mol %, as well as the homopolyester entirely made of these units, were prepared by polycondensation from a melt. The microstructure of the copolymers was determined by NMR to be random for the whole range of compositions. The effect exerted by the 5‐tert‐butyl isophthalate units on thermal, tensile, and gas transport properties was evaluated. Both the melting temperature (T_m) and crystallinity were found to decrease steadily with copolymerization, whereas the glass‐transition temperature (T_g) increased and the polyesters became more brittle. Permeability and solubility slightly increased with the content in substituted isophthalic units, whereas the diffusion coefficient remained practically constant. For the homopolyester poly(5‐tert‐butyl isophthalate), all these properties were found to deviate significantly from the general trend displayed by copolyesters, suggesting that a different structure in the solid state is likely adopted in this case. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 92–100, 2005     

Adsorption thermodynamics of monomers on diluted-bonds triangular lattices

The surface of amorphous solids cannot be usually represented by a regular lattice of adsorbing sites. One of the main characteristics of such surfaces is a variable connectivity for each site. A simple model consisting of a triangular lattice where a fraction of bonds (interactions) is suppressed at random is used here to find out, by using Monte Carlo simulations, how the adsorption thermodynamics of repulsively interacting monomers is modified with respect to the same process in the regular lattice. Adsorption isotherm, differential heat of adsorption and adsorbed phase entropy calculations are carried out showing and interpreting the effects of the variable connectivity. In particular, it is found that the order-disorder phase transition observed for the regular lattice survives, though with modifications, above a critical mean connectivity.     

Sub-monolayer assemblies of octanethiol and octadecylthiol at gold electrodes for the direct analysis of 4,4'-oxydianiline in wastewaters and shoe-dyeing samples

Self-assembled monolayers (SAMs) of di-n-octadecyldisulphide (C(18)) and n-octanethiol (C(8)) were prepared on gold electrodes. From the studies carried out by cyclic voltammetry and square wave voltammetry, it was observed that the electrochemical behaviour of 4,4'-oxydianiline on these electrodes is affected by the length chain of the alkanethiol. After the optimization of all the variables involved in the electrochemical response of 4,4'-oxydianiline by square wave voltammetry employing the modified electrodes, it is possible the determination of 4,4'-oxydianiline with a detection limit of 0.04microg/mL (C(18)) and 0.06microg/mL (C(8)) and determination limits of 0.12 and 0.22microg/mL, respectively. The calculated Er (%)(n=10) and R.S.D.(%)(n=10) values were minor than 2.2% and 3.7%. The proposed methods were successfully applied to the analysis of oxydianiline in wastewater and shoe-dyeing samples.