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.     

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.     

Electrical properties of transparent carbon nanotube networks prepared through different techniques

Ultra‐thin, optically transparent and electrically conducting films of pure carbon nanotubes (CNTs) are widely studied thanks to their promise for broad applications. In the present work, we study and compare different deposition techniques for the production of these networks: dip‐coating, spray‐coating, vacuum filtration and electrophoretic deposition on a quartz glass using single‐walled carbon nanotubes (SWCNTs) produced by the HiPCo method. In order to optimize the networks, besides the various deposition techniques we also investigate how the optical and electrical properties vary if the networks are fabricated from different CNTs, all synthesized by the CVD method: SWCNTs, DWCNTs and MWCNTs. As the main criteria for evaluating the quality of these CNT networks we measure the electrical surface resistance at a certain optical transmittance and correlate it to the morphology (homogeneity and roughness) of the networks. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rectangular to hexagonal columnar phase transition exhibited by a biforked mesogen

We present the structural study of a biforked compound exhibiting a Col_r-Col_h phase transition. This study was performed by means of DSC, optical microscopy, X-ray diffraction, dilatometry and molecular modelling. The molecular packing within the two columnar mesophases of this compound is discussed. For the first time, it is shown that the clusters of adjacent molecules which form the elementary section of a column are tilted with respect to the columnar axis in the rectangular mesophase. From the whole set of experimental data, the number of molecules in a columnar section is found to be about 5 in the rectangular mesophase, and 4 in the hexagonal one. The transition between the two columnar mesophases is discussed with respect to its slow kinetics. Received 1st October 2002 Published online: 16 April 2003 RID="a" ID="a"e-mail: ribeiro@cii.fc.ul.pt RID="b" ID="b"UMR 7504     

SBA splitting for approximation of invariants in time-dependent Hamiltonian systems

Most physical phenomena are described by time-dependent Hamiltonian systems with qualitative features that should be preserved by numerical integrators used for approximating their dynamics. The initial energy of the system together with the energy added or subtracted by the outside forces, represent a conserved quantity of the motion. For a class of time-dependent Hamiltonian systems [8] this invariant can be defined by means of an auxiliary function whose dynamics has to be integrated simultaneously with the system’s equations. We propose splitting procedures featured by a SB³A property that allows to construct composition methods with a reduced number of determining order equations and to provide the same high accuracy for both the dynamics and the preservation of the invariant quantity.     

A new high temperature mesophase of a double-swallow-tailed compound with weak optical anisotropy

A new six-ring double-swallow-tailed compound is presented which shows four liquid crystalline phases. In addition to a smectic C phase and two columnar phases (oblique and hexagonal), a high temperature mesophase was observed which exhibits a very weak birefringence and which shows unusual optical textures.     

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.