Laterally substituted naphthalene-2,7-diol-based bent-shaped liquid crystals

Novel series of laterally 1-substitued (H, Cl, CH₃, CN, NO₂) naphthalene-2,7-diol based liquid crystals were synthesized and their mesomorphic properties identified using DSC studies, texture observation, X-ray investigations and electro-optical measurements. Depending on the chain length and type of lateral substitution, the compounds exhibit a variety of mesophases. In materials with short alkyl chains, the rectangular columnar B₁ phase was found. Increasing the alkyl chain length for the non-substituted core causes the appearance of the so-called B_N phase. In CH₃- and Cl-substituted compounds, the antiferroelectric B₂ phase (SmC_AP_A) was found. Introduction of the CN and NO₂ substituents led to the formation of the B₇ phase.     

Impulse Responses of Fractional Damped Systems

Considered are systems of single-mass oscillators with different fractional damping behaviour. Similar to the classical model, where the damping terms are represented by first derivatives, the eigensystem can be used to decompose the fractional system in frequency domain, if mass, stiffness and damping matrices are linearly dependent. The solution appears as a linear combination of single-mass oscillators. This is true even in the general case such that stability and causality are insured by the same argumentation as used in the linear dependent case.     

Influence of flexible spacers on liquid-crystalline self-assembly of T-shaped bolaamphiphiles

T-shaped bolaamphiphiles composed of a biphenyl rigid core, a semiperfluorinated lateral chain, two polar 1,2-diol groups in the terminal positions and flexible alkyl spacers connecting the polar groups with the biphenyl core have been synthesized and investigated by polarizing microscopy, DSC and X-ray scattering. The influence of spacer length and position of the spacer on the self-assembly in liquid-crystalline phases was studied. A series of four different columnar phases (Col(hex)/p6mm, Col(rec)/p2gg, Col(squ)/p4gm and Col(squ)/p4mm), representing liquid-crystalline honeycomb structures composed of cylinders having hexagonal, pentagonal, and square cross section, were found on increasing the spacer length. It is also shown that introduction of aliphatic spacers in the backbone of the T-shaped bolaamphiphiles replaces the Col(rec)/c2mm phase made up of rhombic cylinders with the Col(squ)/p4mm phase composed of square cylinders. It also causes the 2d lattice of pentagonal cylinders to increase the symmetry from Col(rec)/p2gg to Col(squ)/p4gm. A temperature-dependent second-order phase transition between these two pentagonal cylinder structures was observed for the first time. Beside these effects on cylinder shape and phase symmetry the flexible spacer units also lead to reduced phase transition temperatures and allow adjustment of cylinder side length to envelop a wider range of side-chain sizes. Electron density maps suggest that this may involve sacrificing some of the hydrogen bonds.     

A re-entrant smectic C phase in a sequence smectic C-oblique columnar-smectic C-nematic

A new six-ring double-swallow-tailed compound is presented which exhibits a re-entrant smectic C phase in the sequence smectic C-oblique columnar-smectic C-nematic. This unusual sequence detected by observation of the optical textures and by X-ray investigations is also confirmed by the phase diagrams with homologous compounds.     

Liquid crystalline phases of perfluorinated compounds with segregated sublayers

The liquid crystalline polymorphism (S_A, S_B, CrE) and the structures of the phases of N-n-perfluoralkylethyl-(4-phenylbenzylidene)imines are described. It is shown that the smectic layer consists of two sublayers in to which the incompatible moieties of the compounds segregate. It is proved that the perfluoralkyl chains remain disordered until crystallization occurs, whereas with decreasing temperature, the aromatic parts are ordered in types of S_B and CrE structure.     

Thermotropic biaxial nematic phases with negative optical character [1]

Two disc-shaped multialkynyl arene ethers (1 and 2) with unusual thermo-mesomorphic properties are presented. Conoscopic studies show that the nematic phases of these new low molecular weight liquid crystals are biaxial and that the sign of their biaxiality is negative. The diether 2 is the first discotic twin liquid crystal which exhibits a nematic phase.     

Could Voltammetry be an Effective Alternative Technique to Study Adsorption Kinetics of Electroactive Metal Ions?

The suitability of LSV to study adsorption kinetics of metal ions was evaluated using Cu²⁺ adsorption on Amberlite® IR‐120 as a model system. LSV provided results in agreement with conventional batch method with remarkable decreasing on analysis time and reagents consumption, since no adsorbent/adsorbate separation is required. Adsorption curves can be obtained in situ using only one portion of adsorbate solution. LSV provides higher temporal resolution for adsorption curves, which is indispensable to evaluate adsorption mechanisms and the performance of new adsorbent materials. Therefore, LSV not only saves time and reagents but also provides better quality of kinetic adsorption data.