Unusual rheological effects observed in polyacrylonitrile solutions

Unusual rheological effects have been revealed during the deformation of polyacrylonitrile (PAN) solutions in DMSO. The effects are observed during the study of rheological properties in a wide range of PAN concentrations and are explained by the structuring occurring at low polymer concentrations. At concentrations of at most 0.1%, the solutions exhibit the behavior of soft gels, which are characterized by yield stresses and frequency-independent storage moduli. As concentration is increased, both effects gradually vanish and the solutions are almost transformed into Newtonian liquids. The results have been explained by the formation of a supramolecular spatial structure at low polymer concentrations. As concentration is increased, the role of structuring is suppressed by the formation of a network of intermacromolecular entanglements. The ability of dilute PAN solutions to exist in two states, i.e., with destroyed structuring and in the form of a physical polymer gel, leads to stress self-oscillations and thixotropic effects. The addition of a precipitant (water) to the PAN-DMSO solutions leads to the formation of a gel throughout the concentration range.     

Zein as a source of functional colloidal nano- and microstructures

The application of colloidal particles from natural materials for purposes ranging from the delivery of bioactives to interfacial stabilisation and bulk structuring have recently gained a lot of interest for applications in the field of fast moving consumer goods, nutraceuticals, agricultural formulations and medicine. Zein-a proline rich water insoluble protein obtained from natural and sustainable source has been recently researched to generate colloidal structures that can find a wide range of applications. In this paper, we review the recent progress in the preparation of colloidal structures and their further application as functional materials in the field of delivery of functional ingredients and structuring of bulk phases and interfaces.     

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From M?ssbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.     

Anionic surfactant ionic liquids with 1-butyl-3-methyl-imidazolium cations: characterization and application

For the first time a series of anionic surfactant ionic liquids (SAILs) has been synthesized based on organic surfactant anions and 1-butyl-3-methyl-imidazolium cations. These compounds are more environmentally friendly and chemically tunable as compared to other common ionic liquids. A detailed investigation of physicochemical properties highlights potential applications from battery design to reaction control, and studies into aqueous aggregation behavior, as well as structuring in pure ILs, point to possible uses in electrochemistry.     

Change of water structure by solvents and polymers

Viscosity measurements have been made of water-solvent and water-polymer solutions in a temperature range of 20–60 centigrades. A medium structure temperatureT ₀ was calculated from the Vogel-equation. Water has a structure temperature of 140–150 K, its decrease indicates structure breakage, an increase structure promotion. Pyridine, dioxane, dimethylformamide and urea are structure breakers. This is explained by a shift of the equilibrium — bonded water molecules — nonbonded — to the right. Acetone shows hydrophobic bonding in the same concentration range of 0–10 mole % as the normal alcohols. They are quasifree liquids-structure temperature zero-in the pure state. This is explained by hydrogen bridged dimer formation with the exception of tert-butanol. Its 3 methylgroups sterically prevent dimer formation and cause structuring. Adding urea to methanol-water solutions breaks water structure according to urea concentration but extends the hydrophobic bonding maximum over the whole diagram. Glucose-water solutions have a minimum in the structure temperature diagram. Its left side indicates waterstructure breakage, its right side formation of a new structure forced upon water by the sugar. The equilibrium can be formulated: Waterlike bonded-nonbonded-hetero (solvent)-like bonded, Ribose also shows this minimum but after a short range of heterobondedness the structure is completely broken to nonbondedness.The polymers dextrane and polyvinylpyrrolidone are strong waterstructure breakers. Dextrane much stronger than PVP, it breaks to nonbondedness while PVP maintains a certain structuring, perhaps indicating heterobonding at higher concentrations. Polyacrylamide is a strong structurebreaker. It resembles urea in this sense. Perhaps the solvationwater structure of the NH₂ groups is very different from pure waterstructure. Polyacrylicacid breaks waterstructure completely, if sodiumchloride is added waterstructure is rebuilt again. The only waterstructure promoting polymer is natural gelatine. Perhaps this structure is different from pure water or the watermolecule equilibrium is shifted towards bondedness. The structure temperatures of pure polyethyleneglycoles show a minimum with increasing molecular weight. The high structure temperature of the small chains is explained by long chain assoziates formation through hydrogen bridging. This liquid of long assoziate chains is structured and has a high structure temperature. With increasing molecular weight ringformation instead of linear assoziation becomes possible. These neutral rings form a free liquid. Long chains again have a linear structure and the structure temperature increases at higher molecular weights. Existence of linear chain assoziation of low molecular PEGs is proved with their breakage by adding the chain terminating methanol.Dedicated to Prof. Dr. F. H. Müller.Herrn Chemotechniker D. Ziegler möchte ich für die sorgfältige Durchführung der Messungen sehr danken.Dem Verband der Chemischen Industrie danke ich sehr für die Ermöglichung der Arbeit.     

Ion-induced multiply reentrant liquid-liquid transitions and the nature of criticality in ethanol-water mixture

We report a quite unusual feature of four liquid-liquid reentrant transitions in ethanol (E)+water (W)+ammonium sulfate mixture by meticulous tuning of the ammonium sulfate concentration in a narrow range, as a function of temperature, at atmospheric pressure. Detailed exploration of the intricate phase behavior in terms of E/W sections shows that the range of triple reentrance shrinks with increasing E/W. The behavior of osmotic susceptibility is investigated by light scattering, near the critical point, in the one-phase region by varying the temperature at fixed concentration of the components, in a particular E/W section. The critical exponent of susceptibility (gamma) and correlation length (nu) are observed to have Fisher renormalized Ising values [Phys. Rev. 176, 237 (1968)], with gamma(r)=1.41 and nu(r)=0.718. The effective susceptibility exponent, gamma(eff), exhibits a sharp, nonmonotonic crossover from Ising to mean-field critical behavior, which is completed outside the critical regime. The amplitude of the correlation length, xi(o)(=21.2+/-0.4 A), deduced from light scattering experiment, is an order of magnitude larger than the typical values in usual aqueous electrolyte systems. This value of xi(o) is further verified from small-angle x-ray scattering (SAXS) experiments and found to be consistent. SAXS experiments on the critical sample reveal the presence of long-ranged intermolecular correlations, leading to supramolecular structuring, at a temperature far away from the critical point. These results convincingly demonstrate that the finite length scale arising due to the structuring competes with the diverging correlation length of critical concentration fluctuations, which influences the nonasymptotic critical behavior in this aqueous electrolyte system. The sulphate ions play a dominant role in both structuring and the complex phase behavior.     

Fabrication of superhydrophobic surface from a supramolecular organosilane with quadruple hydrogen bonding

A supramolecular organosilane, 2-(3-(triethoxysilyl)propylaminocarbonylamino)-6-methyl-4[1H]pyrimidinone comprising quadruple hydrogen bonds has been synthesized in one step from commercially available starting materials. The synthesized supramolecular organosilane can be stabilized and phase-separated by dimerization via the linear array of quadruple hydrogen bonds in solution. This property of the supramolecular organosilane has been exploited to fabricate structuring materials having a superhydrophobic surface property. We have successfully generated the interconnected granular structure with adequate roughness for superhydrophobicity via sol-gel process.     

Characterization of nanoscale metal structures obtained by template synthesis

Generating submicron objects made of nanostructured materials is one of the challenges of nanotechnology. A method for producing micron-sized structures without the use of lithographic techniques has been developed. Electrochemical deposition of metals into nanometer-wide parallel pores of porous anodic oxide films on aluminium is used to produce micro- to nano-wires or -tip arrays. The nanoscale structures and the structuring procedure have been investigated by the examination of lateral and cross-sectional specimens by SEM, EDS and XPS. The investigations show the feasibility of generating films with a variety of different compositions, a high density of tips, and tip diameters in the range of 30–150 nm. Furthermore, impedance spectroscopy was used to characterize the properties of the nanostructured surface. The results show a structure and composition dependent behavior due to the large (electrochemically) active surface area.     

Composition effects of thermoplastic segmented polyurethanes on their nanostructuring kinetics with or without preshear

In this work, the structuring mechanism from the molten state of various thermoplastic polyurethanes was analyzed with respect to their composition [polyether or polyester soft segments (SSs), aromatic or aliphatic hard segments (HSs)]. As a preliminary study, the molar mass evolution of the materials with the temperature was quantified. Then, based on rheological experiments and in situ rheo‐small angle X‐ray scattering (SAXS) measurements, the structuring was examined at different temperatures and, particularly, the effect of a preshear treatment was analyzed. The temperature effect can be accounted by an Arrhenius‐like law with an activation energy depending mainly on the HS nature. Moreover, the shear induced structuring phenomenon is highlighted for all the studied thermoplastic segmented polyurethanes. Nevertheless, for the studied range of shear treatments, the SAXS analyses did not reveal any specific orientation. Finally, arguments based on the modification of the quench depth (ΔT = T_ODT ? T) by the shear are given to explain the shear induced structuring phenomenon. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Structure and reactivity of steroids—VI : Long range effects in a series of Δ1,3,5(10)-estratriene compounds

The kinetics of the oxidation of 17β-hydroxy-Δ^1,3,5(10)-estratrienes which differ in D ring size, in C₃, substituent and in the character of fusion of the B and C rings by CrO₃ in AcOH has been studied. An increase in size of the D ring in the substrate diminishes reactivity of the 17β-hydroxy group in the oxidation. It has been found that the reactivities of the 17β and 17β-hydroxy groups of the Δ^1,3,5(10)-estratriene derivatives depend upon the electronic nature of the substituent at C³, explained by a long range effect operating from the A to D ring. The pK'a's of phenolic steroids have been measured and it was shown that introduction of the Δ⁸⁽⁹⁾ double bond increases the degree of dissociation of the phenolic hydroxyl. Expansion of the D ring and also reduction of the 17(17a)-keto group to 17β (17aβ) hydroxy group decreases the degree of dissociation of the phenolic hydroxyl as a result of the long range effect from the D to A ring. A linear correlation has been established between the oxidation and dissociation rate constants, confirming the existence of an interaction between C₃ and C_17(17a) at the expense of the long range effects from the A to D ring and vice versa. The long range effect apparently arises from a combination of inductive and conformational effects of the substituent. The kinetics of enzymic oxidation of 17β-hydroxy-Δ^1,3,5(10)-estratrienes by soluble 17β-estradiol dehydrogenase from human placenta has been investigated. In the case of 17β-hydroxy-Δ^1,3,5(10)-estratrienes of natural configuration, a linear correlation has been established between the values of the maximum rate constant and the oxidation rate constant. An assumption can thus be made about the major role of the contribution of the specific reactivity of the substrate to that of the enzyme-substrate complex, involving the size of the D ring and the long range effect of the substituent at C₃ upon the reaction center at C_17(17a). For 17β-hydroxy-Δ^1,3,5,(10)-estratrienes of the 8-isoconfiguration it is the specific reactivity of the substrate that makes the major contribution to the maximum rate values; this specific activity is a result of the substrate's configuration, which is responsible for the stability of the enzyme-substrate complex.     

Neutron diffraction and computer simulation studies of D-xylose

Neutron diffraction with isotopic substitution (NDIS) experiments and molecular dynamics (MD) simulations have been used to examine the pentose D-xylose in aqueous solution. By specifically labeling D-xylose molecules with a deuterium atom at the nonexchangeable hydrogen position on C4, it was possible to extract information about the atomic structuring around just that specific position. The MD simulations were found to give satisfactory agreement with the experimental NDIS results and could be used to help interpret the scattering data in terms of the solvent structuring as well as the intramolecular hydroxyl conformations. Although the experiment is challenging and on the limit of modern instrumentation, it is possible by careful analysis, in conjunction with MD studies, to show that the conformation trans to H4 at 180 degrees is strongly disfavored, in excellent agreement with the MD results. This is the first attempt to use NDIS experiments to determine the rotameric conformation of a hydroxyl group.     

Diffusive dynamics of water in tert-butyl alcohol/water mixtures

Quasielastic neutron scattering has been used to investigate the dynamical behavior of H(2)O in water/tert-butyl alcohol solutions. The measurements were made at fixed temperature (293 K) as a function of tert-butyl alcohol molar fraction, x, in the range 0-0.042. The data have been compared to those of pure water in the temperature range 269-293 K. The effect of tert-butyl alcohol addition on water dynamics is equivalent to that obtained by lowering the temperature of pure water by an amount proportional to the alcohol concentration. The temperature dependence of the diffusivity parameters in pure water and their concentration dependence in tert-butyl alcohol/water solutions can be rescaled to a common curve attributing to each solution a concentration-dependent "structural temperature" lower than the actual thermodynamic one. These results can be understood in terms of Stillinger's picture of water structuring and of other more recent theoretical pictures that emphasize the influence of the geometrical properties of hydrogen bond networks on water mobility.     

Ultrafast orientational dynamics of nanoconfined benzene

Ultrafast optical Kerr effect spectroscopy has been used to study the orientational dynamics of benzene and benzene-d(6) confined in nanoporous sol-gel glass monoliths with a range of average pore sizes. All of the observed orientational diffusion of confined benzene is found to occur on a slower time scale than in the bulk, even in pores with diameters that are significantly larger than a benzene molecule. The orientational dynamics of benzene-d(6) are found to be inhibited to a lesser extent than those of benzene, which is attributed to the differences in wetting properties of the two liquids on silica. The decays are fit well by a sum of two exponentials, the faster of which depends on pore size. Similar results are found in pores that have been modified with trimethylsilyl groups, although the relaxation is faster than in unmodified pores. Comparison to Raman line width data for confined benzene-d(6) suggests that the liquid exhibits significant structuring at the pore walls, with the benzene molecules lying flat on the surfaces of unmodified pores.     

Diffusion transport of magnesium nitrate aqueous solutions in membranes made of a porous glass

The diffusion coefficients of aqueous solutions of magnesium nitrate in a wide range of the concentrations upon transport in porous glass membranes (pore radius from 4.5 to 70 nm) were determined. The effect of magnesium nitrate concentration on the properties of the diffusion transport in the membranes was studied, based on ideas about the structuring of the boundary layers of water with the silica surface and their destruction under the action of ions.     

Short and long range correlations in liquid crystals composed of non-rod-like molecules

Dielectric data of a polymer siloxane derivative have been analysed. The deviation from the Debye behaviour has been interpreted using the many body, cooperative model. Comparison with the results for liquid crystals composed of elongated molecules has been made from the point of view of short and long range correlations.     

Long-range hydrogen-bond structure in aqueous solutions and the vapor-water interface

There is a considerable disagreement about the extent to which solutes perturb water structure. On the one hand, studies that analyse structure directly only show local structuring in a solute's first and possibly second hydration shells. On the other hand, thermodynamic and kinetic data imply indirectly that structuring occurs much further away. Here, the hydrogen-bond structure of water around halide anions, alkali cations, noble-gas solutes, and at the vapor-water interface is examined using molecular dynamics simulations. In addition to the expected perturbation in the first hydration shell, deviations from bulk behavior are observed at longer range in the rest of the simulation box. In particular, at the longer range, there is an excess of acceptors around halide anions, an excess of donors around alkali cations, weakly enhanced tetrahedrality and an oscillating excess and deficiency of donors and acceptors around noble-gas solutes, and enhanced tetrahedrality at the vapor-water interface. The structuring compensates for the short-range perturbation in water-water hydrogen bonds induced by the solute. Rather than being confined close to the solute, it is spread over as many water molecules as possible, presumably to minimize the perturbation to each water molecule.     

Immbolization of uricase enzyme in Langmuir and Langmuir-Blodgett films of fatty acids: possible use as a uric acid sensor

Preserving the enzyme structure in solid films is key for producing various bioelectronic devices, including biosensors, which has normally been performed with nanostructured films that allow for control of molecular architectures. In this paper, we investigate the adsorption of uricase onto Langmuir monolayers of stearic acid (SA), and their transfer to solid supports as Langmuir-Blodgett (LB) films. Structuring of the enzyme in β-sheets was preserved in the form of 1-layer LB film, which was corroborated with a higher catalytic activity than for other uricase-containing LB film architectures where the β-sheets structuring was not preserved. The optimized architecture was also used to detect uric acid within a range covering typical concentrations in the human blood. The approach presented here not only allows for an optimized catalytic activity toward uric acid but also permits one to explain why some film architectures exhibit a superior performance.     

Effect of additional hydrogen peroxide to H2O2...(H2O)n, n=1 and 2 complexes: quantum chemical study

Hydrogen peroxide, H2O2, acts as a particularly strong reactant in aqueous environment. It has been demonstrated earlier that agglomerates with a single peroxide interacting with one and two water molecules manifest in several stable conformers within a narrow energy range. In the present study we seek structural changes brought out by adding an extra H2O2 to these systems at molecular level employing ab initio quantum chemical methods, viz., restricted Hartree-Fock and the second order Moller-Plesset perturbation theory. These clusters exhibit consistent trends in energy hierarchy at both the levels. Further, a many body interaction energy analysis quantifies the strength and cooperativity of hydrogen bonding in the (H2O2)2...(H2O)n, (n=1 and 2) clusters, bringing out structuring/destructuring effects attributed to attachment of water and hydrogen peroxide molecules.     

Ordering of fluoro-mesogens: a statistical approach based on quantum mechanics and computer simulation

Computational analysis of the molecular ordering of nematic p -phenylene-4-methoxy benzoyl 4-trifluoromethylbenzoate (FLUORO1) and smectic 4-propyloxyphenyl 4-(4-trifluoromethylbenzoyloxy) benzoate (FLUORO2) mesogens has been carried out with respect to translatory and orientational motions. The net atomic charge and atomic dipole components at each atomic centre of the molecule have been evaluated using the CNDO/2 method. Rayleigh-Schrodinger perturbation theory, along with the multicentred-multipole expansion method, has been employed to evaluate long range intermolecular interactions while a '6-exp' potential function has been assumed for short range interactions. The total interaction energy values obtained through these computations were used to calculate the probability of each configuration at the phase transition temperature using the Maxwell-Boltzmann formula. The flexibility of various configurations has been studied in terms of the variation of probability due to small departures from the most probable configuration. The results obtained enable the determination of the peculiarities of the molecular ordering, as well as the construction of models of the structures of FLUORO1 and FLUORO2 in different modes of interaction. The mesophase nature has been correlated with the parameters introduced in this paper.     

Polysulfides as biologically active ingredients of garlic

Garlic has long been considered as a natural remedy against a range of human illnesses, including various bacterial, viral and fungal infections. This kind of antibiotic activity of garlic has mostly been associated with the thiosulfinate allicin. Even so, recent studies have pointed towards a significant biological activity of trisulfides and tetrasulfides found in various Allium species, including a wide range of antibiotic properties and the ability of polysulfides to cause the death of certain cancer cells. The chemistry underlying the biological activity of these polysulfides is currently emerging. It seems to include a combination of several distinct transformations, such as oxidation reactions, superoxide radical and peroxide generation, decomposition with release of highly electrophilic S(x) species, inhibition of metalloenzymes, disturbance of metal homeostasis and membrane integrity and interference with different cellular signalling pathways. Further research in this area is required to provide a better understanding of polysulfide reactions within a biochemical context. This knowledge may ultimately form the basis for the development of 'green' antibiotics, fungicides and possibly anticancer agents with dramatically reduced side effects in humans.