Simultaneous Determination of 4‐Chlorophenol and Oxalic Acid Using an Expanded Graphite‐Epoxy Composite Electrode

An expanded graphite‐epoxy composite electrode (EG‐Epoxy) was employed for the simultaneous determination of 4‐chlorophenol (4‐CP) and oxalic acid (OA) by using cyclic voltammetry (CV), chronoamperometry (CA), and differential pulse voltammetry (DPV). The results indicated that OA could be determined in the presence of the same concentrations of 4‐CP within the concentration range of 0.1 mM to 0.5 mM with a relative standard deviation (RSD) smaller than 5%. Electrode fouling occurred during CA for 4‐CP concentrations larger than 0.5 mM. The DPV method was used for the simultaneous determination of 4‐CP and OA before and after electrochemical oxidation by chronopotentiometry under galvanostatic conditions (j=0.04 mA cm^?2, t=2 h) of a tap water sample spiked with 0.19 mM 4‐CP and 0.1 M Na₂SO₄.     

Changes of the Molecular Mobility of Poly(<Emphasis Type="Italic">ε</Emphasis>-caprolactone) upon Drawing,Studied by Dielectric Relaxation Spectroscopy

Dielectric relaxation spectroscopy (DRS) of poly(ε-caprolactone) with different draw ratios showed that the mobility of polymer chains in the amorphous part decreases as the draw ratio increases.The activation energy of the α process,which corresponds to the dynamic glass transition,increases upon drawing.The enlarged gap between the activation energies of the αprocess and the β process results in a change of continuity at the crossover between the high temperature a process and the α and β processes.At low drawing ratios the a process connects with the βprocess,while at the highest drawing ratio in our measurements,the a process is continuous with the a process.This is consistent with X-ray diffraction results that indicate that upon drawing the polymer chains in the amorphous part align and densify upon drawing.As the draw ratio increases,the α relaxation broadens and decreases its intensity,indicating an increasing heterogeneity.We observed slope changes in the α traces,when the temperature decreases below that at which τα ≈ 1 s.This may indicate the glass transition from the ‘rubbery’ state to the non-equilibrium glassy state.     

Asymmetric oxadiazole mesogens as candidates for low-temperature biaxial nematics

We report the synthesis and properties of a homologous series of asymmetric, mesogenic derivatives of 2,5-bis-(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP). Benzyloxy (BnO-), alkoxy benzoate ester derivatives BnO-ODBP-Ph-O-C _n , where n?=?4, 5, 6, 7, 8, 9, 12, were studied by ²H-NMR, X-ray diffraction and polarising microscopy in order to ascertain if the lower temperature nematic phases exhibited biaxiality. Deuterium nuclear magnetic resonance (NMR) of labelled probes in these asymmetric mesogens does not show evidence of biaxiality. The absence of biaxiality is discussed in terms of the statistical non-linearity of these asymmetric ODBP mesogens.     

Quantum Matrix Pairs

The notion of quantum matrix pairs is defined. These are pairs of matrices with noncommuting entries, which have the same pattern of internal relations, q-commute with each other under matrix multiplication, and are such that products of powers of the matrices obey the same pattern of internal relations as the original pair. Such matrices appear in an approach by the authors to quantizing gravity in 2 space and 1 time dimensions with negative cosmological constant on the torus. Explicit examples and transformations which generate new pairs from a given pair are presented.     

Novel Color-Shifting Mobility Sensitive Fluorescent Probes for Polymer Characterization

1-Methyl-7-dimethylamino quinolinium tetrafluoroborate, a highly stable, highly fluorescent color-shifting mobility sensitive fluorescent probe was employed for detecting the glass transition and phase transitions, notably crystallization, in polymers and polymer blends. Glass transitions in amorphous and semi-crystalline polymers were detected by a change in gradient in emission wavelength λ_max versus T plots. Crystallization resulted in discrete blue shifts in λ_max versus T plots. Selective probing of PMMA in a PS/PMMA blend, down to a PMMA content of 1%, was demonstrated. Dielectric relaxation spectroscopy has established a clear link between the mobility of dipoles in PMMA and the emission wavelength of the fluorescent probe.     

A supramolecular nematic phase in sulfonated polyaramides

A water-soluble polyaramide "sulfo-invert-PPTA" surprisingly, already at a molecular weight of 10,000 g mol(-1), exhibits a nematic liquid crystalline phase in water at very low polymer concentrations, around 1-2wt%, indicating that supramolecular assemblies of molecules are the building blocks of the nematic phase.     

Integration on supermanifolds and a generalized Cartan calculus

A suggestion by Berezin for a method of integration on supermanifolds is given a precise differential geometric meaning by assuming that a supermanifold is the total space of a fibre bundle with connection. The relevant objects for integration are identified as suitable horizontal/vertical projections of hyperforms. The latter are generalizations of differential forms having both covariant and contravariant indices. The exterior calculus of these projected hyperforms is developed, analogously to the Cartan calculus, by introducing appropriate derivations and determining their commutators, respectively anticommutators.     

Sulfonated liquid crystalline polyesters as resin matrix for single wall carbon nanotube and nanodiamond composites

The focus of this study is on incorporating pendant sulfonate groups along the backbone of a liquid crystalline polyester (LCPE) with the aim to improve the dispersion of single wall carbon nanotubes (SWNTs) and nanodiamonds (NDs). Two LCPE matrices, one sulfonated (LCPE‐S) and one nonsulfonated reference polymer (LCPE‐R), were successfully synthesized via a melt condensation method using aromatic and aliphatic AB, AA, and BB‐type monomers. Upon the introduction of SWNT and ND particles, the glass transition temperature (T_g) of the sulfonated LCPE increased from 21.5 °C to 41.0 °C and 41.9 °C, for SWNTs and NDs, respectively. When sulfonate groups were absent, a decrease in T_g was observed. The storage modulus (E′) followed a similar trend, i.e., E′ increased from 1.3 GPa to 5.2 GPa and 3.4 GPa, upon the addition of NDs and SWNTs. The LCPE‐S showed a lower thermal stability due to the loss of sulfonate groups, i.e. the 5% weight loss temperature (T) is ～280 °C for LCPE‐S vs. 333 °C for LCPE‐R. The decomposition temperature increased somewhat upon addition of the nanoparticles. The ability of dispersing carbon‐based nanostructures combined with an accessible melt processing window makes sulfonated LCPs attractive matrices towards preparing nanocomposites with improved thermal and mechanical properties. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.     

Structural evolution of liquid-crystalline solutions of hydroxypropyl cellulose and hydroxypropyl cellulose-based nanocomposites during flow

The phase state and orientation and dissipative characteristics of biphasic LC HPC-water solutions and filled systems formed on their basis during shear flow are studied by various methods. The concentration of solutions is selected on the basis of the corrected phase diagram constructed with the use of optical interferometry. Flow curves and concentration dependences of viscosity provide additional information about the phase state and structure of the samples and the role of fillers in the rheological properties of solutions. X-ray diffraction data are obtained with the use of a Couette cell consisting of two coaxial capillaries. In the case of a clay suspension in water, practically no orientation is attained. However, in the isotropic 30% solution, clay particles easily orient, a result that indicates an important role of the viscoelasticity of a medium in the orientation process. The development of orientation of HPC macromolecules and clay particles in relation to the shear rate is analyzed separately for systems with the biphasic matrix (LC + isotropic phase). In addition, the time decay of the orientation parameter during relaxation is investigated. It is shown that higher shear rates cause a more rapid relaxation of orientation, for which recovery of the cholesteric helix typical for LC solutions of cellulose derivatives in the equilibrium state plays an important role. Order parameters (separately for the two components) are calculated, and their evolution with the shear rate and total deformation is investigated for systems containing clay nanoparticles (also the structure-active component) in LC solutions. On the basis of these data, it is hypothesized that clay particles form the columnar mesophase, which, under certain conditions, may transform into the discotic mesophase. This transition is responsible for a certain decrease in the order parameter of HPC apparently due to the instability effect of the director. It is found that shearing substantially affects the structure of the system composed of two mesophase species; specifically, it either facilitates the reinforcement of one of them or provokes structural transitions.