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.     

Origin of rheological behavior and surface/interfacial properties of some semi-alicyclic polyimides for biomedical applications

High-performance alicyclic-containing polyimides for advanced applications, derived from 5-(2,5-dioxotetrahydrofurfuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylic acid anhydride or bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride and two flexible aromatic diamines, were synthesized by a classical two-step polycondensation reaction and analyzed by rheological method. The results were discussed according to the chemical structure of polyimides and their different properties, such as flexibility, hydrophobicity and surface morphology. It has been showed that the obtained parameters, controlled by the interactions occurring in the polyimide systems, can be correlated with the adhesion/cohesion of blood components and plasma proteins. Thus, the results of the work of spreading proteins on the hydrophobic polyimide surfaces indicated that albumin is not absorbed preferentially, while fibrinogen is characterized by a higher degree of adhesion on the surfaces, and also that selective adsorption of plasma proteins modifies blood compatibility. In addition, these results and the ascertained antimicrobial activity of the studied polyimides contribute to the development of new applications in the bio-technical field.     

Second-Order Correction for Convective Wall Plume in Power-Law Fluids Over an Isothermal Wall

This paper considers the steady-state free-convection flow arising from an infinitely long horizontal line source of heat embedded at the leading edge of a vertical isothermal surface when the ambient fluid is a non-Newtonian fluid, for moderately large values of the generalized Grashof numbers by the method of matched asymptotic expansion. The first- and second-order boundary layer equations are considered. In particular, the second-order corrections to account for the non-boundary layer effects have been predicted. A family of numerical solutions are reported for the power-law fluid behavior index, n, ranging from 0.4 to 1.5 and for Pr = 10 and 100.     

Morphological and structural-rheological relationship in epiclon-based polyimide/hydroxypropylcellulose blend systems

Blends of hydroxypropyl cellulose (HPC) in lyotropic phase have been prepared with a new epiclon- based poly(amic acid) (PAA) or its corresponding polyimide (PI). The flow behaviour of their mixed solutions in N,N-dimethylacetamide (DMAc) was investigated by means of shear viscometry and oscillatory shear tests. The effect of composition, temperature and shear rate on the rheological functions reflects the orientation or mobility of the chain segments in the shear field. Specific interactions, such as the hydrogen bonds between PAA and the liquid crystalline component, stabilized the resulted morphology. The band texture, typical for lyotropic HPC solutions, evidencing different intensities and dimensions is observed from atomic force microscopy images in PAA/HPC and PI/HPC blends. The paper pursues some aspects concerning the obtaining of mixed alignment layers used in display devices.     

Influence of the substitution degrees on the optical properties of cellulose acetates

Cellulose acetates with different substitution degrees possess a set of properties that makes them highly suitable for optical applications. This article discusses some of these properties, namely refractivity, dielectric properties, and transmittance. The contribution of the ratio between the molar refraction, which is proportional to the induced dipole moment, and the molar volume for the different atoms present in the studied polymers to the optical properties was investigated. The study illustrates the importance of such structural and compositional characteristics in tailoring some specific optical applications. Furthermore, optical transmission has been investigated in the 200–1000 nm range. To obtain the optical parameters, the approach proposed by Tauc for amorphous semiconductors has been used because of the similarity of the absorption edges. The values of pseudogap energy ranged between 3.44 and 4.70 eV, whereas those of Urbach energy were modified in the 18–37 meV range. All parameters determined have been related to the influence of the substitution degrees and of the synthesis condition. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Physical characteristics of magnetorheological suspensions and their applications

This paper reviews the potential applications of magnetorheological suspensions along with their rheological and electro-conductive properties under an applied magnetic field. Linked to these physical properties, the range of potential engineering applications of their linear and revolving vibrations include shock absorbers, dampers, clutches, magneto-resistors, magnetic field sensors and ultrafine polishing technology. Improvements in the electrical characteristics of steady current generators, rotary dampers under high and low pressures, kineto-therapeutic devices and medical applications are also covered.     

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.     

Homotopy analysis of unsteady heat transfer started impulsively from rest along a symmetric wedge

In this paper, the unsteady heat transfer over an impulsively started wedge is investigated. The mixed convection, namely, the thermal boundary-layer growth is caused by the sudden increase of the surface temperature as it is set into motion. The analytic approximations with high accuracy are given using the Homotopy–Padé technique, which agree well with the numerical results using an implicit finite-difference method known as Keller–Box method. It is found that the Homotopy–Padé approximations have no relation to the auxiliary parameters ?_f and ?_g, which play important roles in the homotopy analysis method.     

Micropolar fluid flow towards a stretching/shrinking sheet in a porous medium with suction

This paper presents a numerical analysis of a micropolar fluid flow towards a permeable stretching/shrinking sheet in a porous medium. The governing nonlinear partial differential equations are transformed into a system of ordinary differential equations by a similarity transformation, before being solved numerically by a finite-difference scheme known as the Keller-box method. The effects of the governing parameters on the fluid flow and heat transfer characteristics are illustrated graphically. It is found that dual solutions exist for the shrinking case, whereas for the stretching case, the solution is unique.     

Spin-spin relaxation times in myocardial hypertrophy induced by endocrine agents in rat

Magnetic resonance techniques afford a significant advantage for noninvasive diagnosis of cardiovascular pathology. The purpose of our present study was to assay the proton nuclear magnetic resonance (¹H-NMR) sensitivity in the differential diagnosis of certain endocrine cardiovascular complications. In this context, we investigated the water state and content in the hypertrophied myocardium. Male and female Wistar rats were treated with different hormones (hydrocortisone acetate, testosterone, estradiol, thyroid hormones) in combination with isoproterenol (a synthetic catecholamine that induces myocardial ischemia and hypertrophy). The animals were sacrificed after 20 days of treatment and samples of integral myocardium and left ventricular myocardium were analyzed on a¹H-NMR AREMI spectrometer (0.6 T; proton resonance at 25 MHz). The estimation ofT ₂ was made by Carr-Purcell-Meiboom-Gill pulse sequence. The data were fitted to a bi-exponential curve, yielding short (T ₂₁) values forbound water and long (T ₂₂) values forfree water. In order to evaluate the myocardial hypertrophy, the following ratios were calculated: integral myocardium to body weight; left ventricle to body weight; left ventricle to integral myocardium. The first two ratios were also calculated for dried tissue, in order to estimate its contribution to myocardial hypertrophy. Our findings demonstrate that myocardial hypertrophy is associated with a decrease ofT ₂₂, as a consequence of the increase in the dried component (i.e. proteins) of the tissue, while the total tissue, while the total tissue water (H₂O_t%, measured by gravimetry) was not significantly modified. Nevertheless, it is reasonable that the increase in the protein content would be proportional with the increase in H₂O_t%. The decrease ofT ₂₁ seems to be proportional with the level of left ventricle hypertrophy in female groups. The¹H-NMR measurements were much sensitive for the differential diagnosis of myocardial hypertrophy in the case of left ventricle.