Liquid–liquid extraction of copper(II) with substituted salicylideneanilines from sulfate media

The liquid–liquid extraction of copper(II) with Schiff bases in chloroform from sulfate media is studied for pH and concentration of the extractant. Stoichiometry coefficients of the extracted species are determined by the slope analysis method. With salicylideneaniline, the copper(II) is extracted as a mixed chelate complex, CuL₂HL. In the presence of substituent, the copper is extracted as simple chelates, CuL₂. The trends in the values of extraction constants were explained in terms of the nature of the substituents.     

Control the self-assembly of fluorenone-based polycatenars by tuning chain length

Using Suzuki coupling reactions as key steps, a series of fluorenone-based polycatenars, consisting of a central 2,7-diphenyl-9-fluorenone core connected with the 3,4,5-trialkoxybenzoate unit via –COO- linkage at each side have been synthesized. Upon elongation of the terminal alkyl chain, these compounds self-assembled into mesophase sequence of Col_hex/p6mm - Cub_I/$\mathit{Pm}\overline{3}n$ in solid states as well as organogels with interesting morphologies varied from 3D helical fibers to spherical structures in solvents.     

Emergent biaxiality in nematic microflows illuminated by a laser beam

Anisotropic fluids (e.g. liquid crystals) offer a remarkable promise as optofluidic materials owing to the directional, tunable, and coupled interactions between the material, flow, and the optical fields. Here we present a comprehensive in silico treatment of this anisotropic interaction by performing nonequilibrium molecular dynamics simulations. We quantify the response of a nematic liquid crystal (NLC) undergoing a Poiseuille flow in the Stokes regime, while being illuminated by a laser beam incident perpendicular to the flow direction. We adopt a minimalistic model to capture the interactions, accounting for two features: first, the laser heats up the NLC locally; and second, the laser polarises the NLC and exerts an optical torque that tends to reorient molecules of the nematic phase. Because of this reorientation the liquid crystal exhibits small regions of biaxiality, where the nematic director is one symmetry axis and the axis of rotation for the reorientation of the molecules is the other one. We find that the relative strength of the viscous and the optical torques mediates the flow-induced response of the biaxial regions, thereby tuning the emergence, shape and location of the regions of enhanced biaxiality. The mechanistic framework presented here promises experimentally tractable routes toward novel optofluidic applications based on material-flow-light interactions.     

LIQUID CRYSTALLINE POLYMERS. IV. THERMOTROPIC LIQUID CRYSTALLINE POLY(ARYLIDENE-ETHER)S AND COPOLYMERS CONTAINING N-METHYLPIPERIDONE LINKED TO THE MAIN CHAIN THROUGH SPACERS OF VARIOUS LENGTHS

Two novel series of poly(arylidene-ether)s and copoly(arylidene-ether)s were synthesized from N-methylpiperidone and/or cyclohexanone respectively. The first series (homopolymers) was derived from 4,4′-diformyl-α,ω-diphenoxyalkane or 4,4′-diformyl-2,2′ dimethoxy-α,ω-diphenoxyalkane with N-methylpiperidone. The second series (copolymers) was derived from the diphenoxyalkanes (I–VIII) with N-methylpiperidone and cyclohexanone. The inherent viscosities of the polymers thus prepared were in the range of 0.37–0.98 dI/g. The majority of the polymers and copolymers are soluble in chlorinated hydrocarbons. DSC measurements and microscope observation under polarized light demonstrate that this type of poly(arylidene-ether)s form nematic mesophase over a wide temperature range in contrast to the corresponding copoly(arylidene-ether)s. All of the polymers and copolymers exhibited thermotropic liquid crystalline properties. In most cases, the mesophase extends up to 315°C, where thermal decomposition prevents further observation. The morphology of polymer IXb and copolymer XIb as a selected example was examined by scanning electronic microscope.     

NONLINEAR OPTICAL PROPERTIES OF MOLECULAR TWINS

Three different series of twin nonlinear optic (NLO) molecules were studied, in which the two NLO chromophores are linked by a central flexible polymethylene spacer. The first series, which had two azobenzene chromophores (Azo-twins), was designed to also exhibit liquid crystallinity. Most of the members of this series exhibited a nematic mesophase. The second series had two 4-nitrophenol units as chromphores (PNP-twins), while the third one was based on 4-alkylsulfonyl-4'-alkoxy azobenzene chromophores (Sulfazo-twins). These twin NLO systems exhibited interesting odd-even oscillations in their second harmonic generation (SHG) efficiencies in the powder form. When the spacer had an odd number of methylene groups, they exhibited significantly higher powder SHG efficiency than their even counterparts, with the even ones most often exhibiting no detectable SH signal. Preliminary single crystal X-ray diffraction studies performed on the PNP-twin series showed that while the even members possess a molecular center of symmetry and pack centro-symmetrically, the odd ones do not, leading to the observed alternation. The orientational-disordering dynamics of two of the twin series – the PNP and the Sulfazo-twin series, doped in a poly(methyl methacrylate) matrix, was also studied by monitoring the SH-signal decay in electric field poled samples. Interestingly, the maximum attainable SH signal, χ⁽²⁾, in the poled samples also showed an odd-even oscillation with the odd ones again exhibiting a higher value of χ⁽²⁾. The temporal stability of the SHG intensity at 70°C, after the removal of the applied corona, was also studied and the relaxation of the chromophores was found to follow a biexponential decay. The slower relaxation component exhibits a spacer length dependence, which suggests the interplay of two factors in governing the temporal stability in such polymer doped twin systems, one is the conformational discomfort experienced by the spacer in adopting a U-shaped geometry, and the other the electrostatic repulsion when two aligned dipoles lie very close to each other.     

Study of the electrocaloric effect in ferroelectric liquid crystals

ABSTRACT

Electrocaloric effect (ECE) in two ferroelectric liquid crystalline (FLC) materials has been evaluated by mean of two indirect characterization methods: the photopyroelectric (PPE) technique and the polarization current reversal one. The obtained results show a good correspondence of the adiabatic temperature change associated with the ECE evaluated from both methods. This validates the possibility to use the PPE technique to investigate the ECE in FLCs. This study also demonstrates that FLCs can be used as electrocaloric material. More particularly, it shows that as for their solid homologous, liquid crystals displays more pronounced ECE in the vicinity of a first order transition than that measured near to second-order one.     

The effect of ethanol on the phase behaviour and micro-rheology of liquid crystals

The effect of ethanol on the phase behaviour and micro-rheology of lyotropic liquid crystals (LC) has been studied using a binary mixture of monoglyceride (MG) and aqueous ethanol. The phase behaviour study reveals the structural modulation of surfactant aggregates with increasing ethanol concentration, namely a bicontinuous cubic phase (Ia3d) transitions to the lamellar phase (L_α), at a fixed MG concentration. This behaviour is explained by considering the critical packing parameter (CPP) of the surfactant molecule. Because ethanol dehydrates the surfactant head group (a _s), the CPP values increase (decreasing a _s) and thus the formation of larger CPP aggregates is favoured (i.e., the Ia3d–L_α transition occurs). Cross-polarised images and X-ray scattering data support this conclusion. The structural modulation of the LC has further been investigated using a diffusing wave spectroscopy technique. The correlation and relaxation times, determined from the intersection point at short and long time scales of the mean square displacement (MSD), decrease with increasing concentrations of ethanol, indicating structural modulation of the LC. The micro-viscoelastic moduli (G′ and G′′) derived from the Laplace transformation of the MSD decrease with increasing ethanol concentrations, due to the LC modulation. The thermal effects on the micro-rheology of the LC have also been studied.     

Nonflammable nonaqueous electrolytes for lithium batteries

As the energy density of state-of-the-art lithium (Li)-ion batteries (LIBs) increases, the safety concern of LIBs using liquid electrolytes is drawing increasing attention. Flammability of electrolytes is a critical link of the overall safety performance of LIBs and Li metal batteries. For this reason, intensive efforts have been devoted to suppressing the flammability of liquid electrolytes. In this short review, the common approaches to reduce the flammability of the nonaqueous liquid electrolytes will be summarized. The advantages and limitations of these approaches will also be discussed.     

Dual-Metal Electrolytes for Hybrid-Ion Batteries: Synergism or Antagonism?

The construction of hybrid metal-ion batteries faces a plethora of challenges. A critical one is to unveil the solvation/desolvation processes at the molecular level in electrolytes that ensure efficient transfer of several types of charge carriers. This study reports first results on simulations of mixed-ion electrolytes. All combinations of homo- and hetero-binuclear complexes of Li⁺, Na⁺ and Mg²⁺, solvated with varying number of ethylene carbonate (EC) molecules are modeled in non-polar and polar environment by means of first principles calculations and compared to the mononuclear analogues in terms of stability, spatial organization, charge distribution and solvation/desolvation behavior. The used PF₆⁻ counterion is shown to have minor impact on the geometry of the complexes. The desolvation energy penalty of binuclear complexes can be lowered by the fluoride ions, emerging upon the PF₆⁻ decay. These model investigations could be extended to rationalize the solvation structure and ionic mobility in dual-ion electrolytes.     

Biselective refocusing pulses and the SERF experiment

The SERF experiment is a variant of the homonuclear J-resolved experiment, in which a single coupling constant is measured. It consists of a single chemical shift selective excitation that is followed by a biselective spin echo. Recent articles mention the existence of artefacts in SERF spectra that are supposedly related to pulse imperfections. This article presents a detailed study of the biselective refocusing pulses. It also reports a method for predicting the position and amplitude of the expected and unexpected 2D spectral peaks in SERF spectra. Artefacts can be partially eliminated by phase cycling or by the introduction of static field gradient pulses in the acquisition sequence. A procedure to obtain of pure absorption peaks in SERF spectra is proposed.