Surface properties and biocompatibility of cellulose acetates

The article describes some properties of cellulose acetates (CAs) with different substitution degrees. The hydrophilic/hydrophobic properties, morphological aspects, and interface properties with red blood cells and platelets are affected by the substitution degree, synthesis conditions, history of the formed films from solutions in acetone/water nonsolvent/nonsolvent mixtures, and low pressure plasma treatment. The results obtained are useful in biomedical applications, including evaluation of bacterial adhesion onto surfaces, or utilization of CA for semipermeable membranes. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of thiophene functionalized polystyrene copolymers and their electrochemical properties

Thiophene functionalized polystyrene samples (TFPS) were synthesized by atom transfer radical polymerization (ATRP) of styrene, followed by Suzuki coupling with 3‐thiophene (Th) boronic acid. Conducting graft polymer of TFPS with thiophene was achieved at 1.5 V in tetrabutylammonium tetrafluoroborate/dichloromethane (TBAFB/DM) by electrochemical methods. Spectroelectrochemical analysis of the resulting copolymers [P(TFPS‐co‐Th)] reflected electronic transitions at 449, 721 and 880 nm, revealing π ? π* transition, polaron and bipolaron band formation, respectively. We also successfully established the utilization of dual type complementary colored polymer electrochromic devices using P(TFPS‐co‐Th)/poly(3,4‐ethylenedioxythiophene (PEDOT) in sandwich configuration. The switching ability, stability and optical memory of the electrochromic device were investigated by UV–visible spectrophotometry and cyclic voltammetry. Device switches between brown and blue color with a switching time of 1.3 s were prepared with optical contrast (%ΔT) of 25 %. Copyright © 2005 Society of Chemical Industry     

Sorption and diffusion measurements in ternary polymer-solvent-solvent systems by means of a magnetic suspension balance—Experimental methods and correlations with a modified Flory-Huggins and free-volume theory

Diffusion and sorption data of methanol and toluene in the ternary system methanol-toluene-poly(vinylacetate) (pvac) were measured by means of a magnetic suspension balance (MSB). Ternary diffusion coefficients were determined from sorption kinetics with a method of Crank [1975. The Mathematics of Diffusion, second ed. Claredon Press, Oxford] classically used for binary polymer solvent systems. Assumptions and limitations for this method are discussed. Sorption data of methanol and toluene in the ternary system were correlated with a modified Flory-Huggins theory taking four instead of three interaction parameters into account and compared with predictions of UNIFAC-FV. All four binary Flory-Huggins interaction parameters were correlated as a function of concentration, determined from binary polymer-solvent sorption measurements and from solvent-solvent equilibrium data. The modified Flory-Huggins approach for ternary systems predicts the two limiting cases for the binary polymer-solvent as well the two solvent-solvent equilibria. Diffusion coefficients determined from sorption kinetics measurements were correlated with free-volume theory predictions of Vrentas et al. [1984. Self diffusion in polymer-solvent-solvent systems. Journal of Polymer Science, Polymer Physics Edition, 22, 459-469] and compared with a few available literature data from Surana et al. [1998. Diffusion and equilibrium measurements in ternary polymer-solvent-solvent systems using inverse gas chromatography. Industrial and Engineering Chemistry Research, 37, 3203-3207]. Cross diffusion terms are not taken into account. Diffusion and sorption data, determined with this gravimetric method, were used in model simulations with modified Flory-Huggins and free-volume theory to predict drying curves of ternary methanol-toluene-pvac solutions. The results were compared with previously published experimental results performed by means of Inverse-Micro-Raman-Spectroscopy (IMRS) from Schabel [2004. Trocknung von Polymerfilmen - Messung von Konzentrationsprofilen mit der Inversen-Mikro-Raman-Spektroskopie. Ph.D. Thesis, Universität Karlsruhe (TH), Germany].     

Adaptive attenuation of unknown and time‐varying narrow band and broadband disturbances

In many classes of applications like active vibration control and active noise control, the disturbances can be characterized by their frequency content and their location in a specific region in the frequency domain. The disturbances can be of narrow band type (simple or multiple) or of broad band type. A model can be associated to these disturbances. The knowledge of this model allows to design an appropriate control system in order to attenuate (or to reject) their effect upon the system to be controlled. The attenuation of disturbances by feedback is limited by the Bode Integral and the ‘water bed’ effect upon the output sensitivity function. In such situations, the feedback approach has to be complemented by a ‘feedforward disturbance compensation’ requiring an additional transducer for obtaining information upon the disturbance. Unfortunately, in most of the situations, the disturbances are unknown and time‐varying and therefore an adaptive approach should be considered. The generic term for adaptive attenuation of unknown and time‐varying disturbances is ‘adaptive regulation’ (known plant model, unknown, and time‐varying disturbance model). The paper will review a number of recent developments for adaptive feedback compensation of multiple unknown and time‐varying narrow band disturbances and for adaptive feedforward compensation of broad band disturbances in the presence of the inherent internal positive feedback caused by the coupling between the compensator system and the measurement of the image of the disturbance. Some experimental results obtained on a relevant active vibration control system will illustrate the performance of the various algorithms presented. Some open research problems will be mentioned in the conclusion. Copyright © 2015 John Wiley & Sons, Ltd.     

Study of gradual porous metallic membranes obtained by powder sedimentation

In our preliminary studies the possibility of obtaining sintered porous materials with gradual structure by sedimentation of metallic powder was demonstrated. In this paper we continued our studies on the influencing factors of the sedimentation of metallic powders. Irregular and spherical nickel particles were used having a grain size in the 2–90 μm range measured by the laser scattering particle size analyzer. The particles with irregular shape and larger diameter can sediment faster than the spherical and the smaller diameter particles. The sedimentation rate is also influenced by the sedimentation medium and the quantity of the dispersant agent. Deviations from Stokes law was observed in the case of the irregular particles. The gradual structure is influenced by the sintering regime and the powders characteristics too. The obtained structures were characterized by scanning electron microscopy and mercury porosimetry. The permeability and the filtration fineness were also determined.     

Synthesis and self-assembly of fluorene-vinylene alternating copolymers in “Hairy-Rod” architecture: side chain – mediated tuning of conformation,microstructure and photophysical properties

In the present work, we demonstrate that the side chain choice, as a tunable parameter, is an effective strategy to drive molecular ordering, packing motifs and overall microstructure of a conjugated polymer. By applying Wittig polycondensation novel ‘rod-coil’ structures, in ‘hairy-rod’ architecture, based on fluorenylene vinylene copolymers with well-defined oligomeric side chains were synthesized using ‘T’-shaped or ‘Cross’-shaped p-terphenyl macromonomers. The overall character of the copolymers was systematically varied by attaching of hydrophilic PEG 2000, hydrophobic polar oligo-ε-caprolactone or hydrophobic and non-polar oligostyrene side chains. Self-assembling of the copolymers by simple direct dissolution method was achieved in various solvents by modifying their selectivity in relation to the side chain or main chain. The morphology investigations demonstrated that unique nanofeatures obtained in each case (helical foldamers, vesicles, disks, or helical turns) depend on the nature, number, and position of the side chains which influence the photophysical properties. The ‘hairy-rod’ topology is also responsible for the self-assembly of the materials in molten state, as thermal analysis revealed, and the propensity of the new synthesized conjugated main chain for helical folding was evidenced, as well.     

Impedimetric detection of dopamine on poly(3-aminophenylboronic acid) modified skeleton nickel electrodes

Detection of biologic compounds in particular dopamine is usually based on the complexation between boronic acid groups and diols. For this reason the development of new sensors based on direct monitoring of boronic acid–diol complexation is attractive. A measurable electric response due to a change in the dopamine concentration can be achieved on electrodes modified with boronic groups. In this work a modified electrode has been obtained by electropolymerization of 3-aminophenylboronic acid in aqueous solutions on a preformed polyaniline layer electrochemically deposited on smooth and skeleton nickel electrodes. The modified electrodes have been tested as impedimetric sensors for the detection of dopamine in aqueous phosphate buffer at pH = 7.4. Both sensors gave a linear response for dopamine concentrations between 10^?5 and 10^?10 mol L^?1. Poly(3-aminophenylboronic acid) modified skeleton nickel electrode has the advantage of an increased specific surface area, that lead to a high density of boronic acid groups and hence to a better sensitivity.