bluuebunny/crossref_metadata_2025_split huggingface dataset:
Branching kinetics of epoxy polymerization of 1, 4‐butanediol diglycidyl ether with cis‐1, 2‐cyclohexanedicarboxylic anhydride
Authors: Wu Chi , Chu Benjamin , Stell George 
Published: March 2011

AbstractThe copolymerization of an epoxy resin [1, 4‐butanediol diglycidyl ether (DGEB) (Note a)] with an anhydride [cis‐1, 2‐cyclohexanedicarboxylic anhydride (CH)] in the presence of N, N‐benzyldimethylamine (CA) as a catalyst produces a branched epoxy polymer. We show that the branching kinetics of the copolymerization reaction and the molecular weight distribution of the branched polymers can be approximated by using Smoluchowski's coagulation equation. In the simplest relevant application of this equation to our problem, the overall rate kernel w(u, v) that describes the branching probability in the equation turns out to be proportional to the sum of active sites on the two polymers with a time dependent coefficient. The molecular weight distribution (MWD) and the weight average molecular weight of the branched copolymers at different reaction stages before the gelation threshold are calculated theoretically. The calculated values are then compared with the experimental results obtained by using small angle X‐ray scattering (SAXS), laser light scattering (LLS), and chemical analysis. Satisfactory agreement between experimental results and the use of the coagulation equation is attained when it is assumed that the distribution of epoxy polymer molecules is exponential in the number of branching points or, equivalently, active sites, at an early stage of the polymerization reaction.
Networks from dicyanate of bisphenol a and diphenols
Authors: Bauer M. , Bauer J. , Jährig S. 
Published: March 2011

AbstractNetworks were prepared by copolycyclotrimerization of aromatic dicyanates with diphenols in bulk. The main reactions and structural elements were found and the network building process was modelled by cascade theory combined with a model of the reaction kinetics. Good agreement between theory and experiment is shown.
Synthesis and characterization of polymers based on the cyanate functional group
Authors: Gupta Anshu M. , Macosko Christopher W. 
Published: March 2011

AbstractThe chemistry and growth of polymer structures based on the cyanate linkage has been studied. The monofunctional model compound 2‐(4‐cyanatophenyl)‐2‐phenylpropane was used to study the reaction products. The synthesis was performed with four different transition metal catalysts and also without a catalyst. The quenched products were analyzed using Size Exclusion Chromatography(SEC) and 13C NMR. It was found that the reaction is relatively clean, with trimerization being the major product. A few side products were also detected, which included dimers and higher oligomeric species. Crosslinked polymers were synthesized without catalyst based on the bifunctional monomer 2, 2‐bis(4‐cyanatophenyl)propane. The structure was analyzed using 13C NMR. The conversion and number‐average degree of polymerization based on 13C NMR is reported. Conversion at the gel point was found to be higher than 60%. On this basis it was concluded that polymerization based on cyanate linkages at the conditions studied is diffusion controlled and therefore not described by Flory's mean‐field theory.
The role of mechanical phenomena during the formation of network polymers
Authors: Rozenberg B. A. , Irzhak V. I. 
Published: March 2011

AbstractA review of new results concerning the role of mechanical phenomena during cure of epoxy matrices has been made. The influences of various factors (temperature, nature and concentration of components, the character of adhesion interaction of matrix and filler, etc.) on the rate of structural relaxation of polymer have been examined. The problem of the mechanical degradation of network chains under the action of internal stresses has been discussed.
Rheological studies of the gelation kinetics of Cr+3‐polyacrylamide solutions
Authors: Gallino Germana , Molinari Mario , Lockhart Thomas P. 
Published: March 2011

AbstractA new rheological approach for the study of the gelation kinetics of aqueous Cr+3 polyacrylamide solutions has been investigated which relies on the assumption that at the gel point, GP, a constant amount of Cr+3 will have reacted, independent of the initial Cr+3 concentration. From this, a kinetic expression relating GP to the initial concentrations of Cr+3 and reactive groups on the polymer has been derived for the case of a crosslinking reaction first order in Cr+3 and polymer. Experimental evidence that the amount of Cr+3 reacted at the GP is constant for a given polymer and solution pH has been obtained. The good fit of the kinetic expression to the rheological data provides new evidence that the gelation reaction is first order in Cr+3 rather than second order as claimed previously.
Segmental orientation and infrared dichroism of model bimodal elastomeric networks
Authors: Hanyu Aiko , Stein Richard S. 
Published: March 2011

AbstractModel bimodal networks of polytetrahydrofuran (PTHF) were prepared by end‐linking reactions. They consist of two different molecular‐weight species designated L (long) and S (short). With the S, the hydrogen atoms were replaced by deuterium, so that C‐H and C‐D infrared bands could be associated with the L and S species, respectively. Infrared dichroism could then be used to determine the second‐order orientation function, P2, for each species. Kuhn and Grün's (K‐G) rubber elasticity theory permits a calculation of P2 as a function of the elongation ratio, λ. For the unimodal system, the P2 was found to become greater with decreasing molecular weight between crosslinks, Mc, and is consistent with the theory. For the bimodal network system, the P2 for the L species was found to be almost equal to the P2 for the S species, suggesting a heterogeneous (or non‐affine) deformation of the S and L chain segments at molecular level. In another way, the equality of (P2)L and (P2)S allows us to assume that the bimodal network can be treated as the “unimodal” network consisting of the chain segments with the weight‐averaged length between the long and short chains. Under the assumption of affine deformation for such an “averaged unimodal” system, the number of statistical segments, N, was evaluated using the K‐G theory; the value of N is linearly proportional to the averaged molecular weight between the L and S species and one statistical segment was found to consist of three tetrahydrofuran (THF) monomeric units.
On the elastic and swelling behaviour of swollen poly(vinyl alcohol) networks filled with anisometric colloidal iron(III) hydroxide sol particles
Authors: Zrinyl M. , Kilian H.‐G. , Dierksen K. , Horkay F. 
Published: March 2011

AbstractA new method of preparing filled networks has been developed. Well‐characterized, colloidal iron(III) hydroxide particles are incorporated into chemically cross‐linked poly(vinyl alcohol) gels. Evidence for the random distribution of individual particles is provided by transmission electron microscopy. A filler‐induced gel collapse was observed when the strength of repulsion forces between filler particles is decreased by the screening of Coulombic interactions with electrolytes.
Diffusion in microstructured block copolymer solutions
Authors: Balsara N. P. , Eastman C. E. , Foster M. D. , Lodge T. P. , Tirrell M. 
Published: March 2011

AbstractThis work explores the effect of heterogeneity of chemical composition on tracer diffusion, when the characteristic size of the heterogeneities approaches that of the diffusing molecule. A heterogeneous environment is created by the self‐assembly of diblock copolymers in solution. The system chosen for this study is polystyrene‐polyisoprene diblock copolymers in toluene, which is a common solvent for the two blocks. Above a certain critical concentration, these systems are known to microphase separate into swollen domains of polystyrene and polyisoprene. Diffusion of homopolystyrene through the microstructure is measured in this work. The characteristics of the microstructure are varied by studying block copolymers of different molecular weights and compositions. The tracer diffusion coefficients of the labelled polystyrenes are measured by forced Rayleigh scattering, while the microstructure of the matrix is inferred from small angle X‐ray scattering measurements.In this paper, we report results for the diffusion of polystyrenes (molecular weights 3.2 × 104 and 9.0 × 104) in microstructured solutions of three copolymers. Two copolymer samples forming lamellae of alternating polystyrene and polyisoprene microphases and one sample forming polystyrene cylinders embedded in a polyisoprene matrix have been examined. The data indicate that the tracer diffusion coefficient of 3.2 × 104 molecular weight polystyrene in lamellar and cylindrical solutions is comparable to that of the homopolymer in a homogeneous solution of the same concentration. In contrast, the diffusion of 9.0 × 104 molecular weight polystyrene is substantially slower in the structured solutions than in unstructured solutions of the same concentration. For example, the diffusion coefficient of 9.0 × 104 molecular weight polystyrene in a 47% block copolymer solution with cylindrical microstructure is lower than its value in a homogeneous solution of the same concentration by a factor of 30.
The effect of polymer network structure on diffusive transport across chemically controlled membranes
Authors: Adler K. P. , Weiss A. M. , Grodzinsky A. J. , Yarmush M. L. 
Published: March 2011

AbstractThis paper focuses on the relationship between diffusive transport and membrane composition (crosslinker content and relaxed polymer volume fraction) in membranes whose permeability can be actively controlled by chemical or electrical stimuli. First, pH induced changes in permeability to uncharged fluorescent solutes were measured. Then, by correlating bath pH with membrane hydration, the transport properties of membranes of different crosslinker content and/or relaxed polymer volume fraction were compared at constant hydration.The membrane permeability was found to decrease as the amount of crosslinker added to the membrane formulation at the time of polymerization increased, while the permeability increased as the solvent content during polymerization increased. A free volume theory which was fit to the data shows good agreement, and predicts a monotonically decreasing porosity factor with increased crosslinker content.
Nuclear reaction analysis: A study on the interface formation in polymer mixtures below the critical point
Authors: Steiner U. , Chaturvedi U. K. , Zak O. , Krausch G. , Schatz G. , Klein J. 
Published: March 2011

AbstractWe describe a method for directly determining the composition profile of deuterated polymer chains in polymer mixtures. Our technique, nuclear reaction analysis, is based on the 2H(3He, 4He)1H nuclear reaction. By detecting 4He in a forward geometry, we achieve a spatial resolution of 14 nm (FWHM). We use this technique to probe the broadening of the interface between two partially miscible polymers. We found that such a system attains a finite interfacial width in equilibrium. For short times, we monitor the dynamics of interface formation. We found that the interfacial width increases significantly slower than in the case of free diffusion.
Functional polymeric monolayers and liposomes
Authors: Zaitsev S. Yu , Zubov V. P. 
Published: March 2011

AbstractSome lipid‐like monomers were synthesized by acylation of synthetic and naturally occurring amine‐containing lipids with acryloyl chloride. The surfactant properties and peculiarities of polymerization of lipid‐like monomers in oriented systems were investigated. On the basis of such monomers, polymeric monolayers and liposomes were prepared that have the structural similarity to biomembranes and enhanced stability. The applicability of such systems for immobilization of membrane proteins was shown for the example of bacteriorhodopsin.
Spectroscopic studies of the stability of monolayers of 2‐docosylamino‐5‐nitropyridine at the air/water interface
Authors: Decher Gero , Klinkhammer Frank 
Published: March 2011

AbstractMonolayers of 2‐docosylamino‐5‐nitropyridine (DCANP) at the air/water interface were investigated by UV/Vis spectroscopy. The combination of this method with the classic constant‐area relaxation technique yields insight into the longtime stability and the collapse behavior of monolayers. We have demonstrated that monolayers of DCANP are certainly stable under standard deposition conditions. At surface pressures above 20 mN/m monolayer instabilities lead to the formation of a three‐dimensional head‐to‐head multilayered structure.
Optical waveguiding and nonlinear optical characterization of 2‐docosylamino‐5‐nitropyridine Langmuir‐Blodgett films
Authors: Bosshard C. H. , Küpfer M. , Flörsheimer M. , Günter P. , Pasquier C. , Zahir S. , Seifert M. 
Published: March 2011

AbstractWell ordered Y‐type Langmuir‐Blodgett (LB) multilayers of 2‐docosylamino‐5‐nitropyridine (DCANP) have been characterized with linear and nonlinear optical techniques. The nonlinear optical susceptibilities have been determined for the wavelengths λ = 1064 nm (d33 = (7.8±1) pm/V, d31 = (2.0 ± 0.5) pm/V) and λ = 1318 nm (d33 = (5.6 ± 1) pm/V). Waveguiding experiments with grating couplers allowed the excitation of TEo and TMo modes propagating over more than 20 mm. Guided wave attenuation coefficients as low as 12 dB/cm (at the wavelength λ = 632.8 nm) are reported. Coupling experiments allowed the determination of the dispersion of the refractive index n3 (n3632.8 nm = 1.598). The refractive index data could be used to calculate phase‐matching conditions for frequency doubling with TE modes in DCANP waveguides.
Synthesis Of 2‐D polymer from semi‐amphiphilic Langmuir‐Blodgett (LB) films
Authors: Porteu Florence , Palacin Serge , Ruaudel‐Teixier Annie , Barraud André 
Published: March 2011

AbstractSemi‐amphiphilic monolayers formed via adsorption of tetraethynylpyridinium porphyrins to a dihexadecyl phosphate monolayer are allowed to react with ammoniacal silver nitrate or ammoniacal cuprous chloride, in order to form two‐dimensional polymolecular species in which silver diacetylide groups or diacetylenic bonds are expected to link adjacent coplanar macrocycles. Evidences are given for the formation of these ultrathin two‐dimensional networks.
Monolayer phases of the fatty acids and their ethyl esters
Authors: Bibo Anna Maria , Knobler Charles M. , Peterson Ian R. 
Published: March 2011

AbstractThe miscibility correspondence between water‐surface monolayer phases of the fatty acids and their ethyl esters was determined. Ester phases were found corresponding to all the known phases of the acids, and vice versa, in similar relative positions of the π‐T diagram. Evidence is presented for the existence of a ninth distinct miscibility category, represented by a phase in each of the pure materials, and a tenth found only in mixtures. We propose a tentative correspondence to bulk smectic miscibility categories.
Fluorescence as probe for transport and lateral order in vapor grown Langmuir‐Blodgett(LB) multilayer‐type single crystals of anthracene chromophores with fatty acid tails
Authors: Weiß D. , Kietzmann R. , Storck W. , Lehnert J. , Willig F. 
Published: March 2011

AbstractFluorescence spectra of anthracene moieties with fatty acid tails attached at the 2‐position are reported for Langmuir‐Blodgett(LB)‐type multilayer configurations obtained as single crystals in the gas phase. These systems are considered the best ordered experimental model systems for chromophores with fatty acid tails arranged in the LB multilayer configuration. Closest agreement of the fluorescence spectrum with that of the unsubstituted anthracene crystal is found for the 4‐(2‐anthryl)‐1‐butanoic acid (2A4) crystal. Packing of the anthracene moieties is very similar in both crystals. Low‐temperature spectra (10 K) reveal strong broadening of the peaks due to spatial disorder in the 2A4 crystal. 7‐(2‐Anthryl)‐1‐heptanoic acid (2A7) crystals and even more so actual 2A7 LB multilayers have less structured fluorescence spectra that extend further to lower energies. Picosecond time resolved fluorescence decay curves show exciton transport and trapping in low energy traps. Compressed ground state pairs with excimer‐type spatial configurations are excited directly in the red (476 nm) to emit structureless excimer‐type fluorescence.
Concentration dependence of the electro‐optical spectra from two‐dimensional aggregated chromophore systems
Authors: Grewer Georg , Lösche Mathias 
Published: March 2011

AbstractThe linear and the quadratic Stark effects have been employed to characterize aggregate formation of an amphiphilic cyanine dye mixed with arachidic acid in various concentrations within Langmuir‐Blodgett multilayers. Two different electrode configurations with the electric field directions parallel and normal to the films have been employed to test the responses of the electronic spectra to external fields. The observations have been used to quantify the induced and static dipole moment changes on excitation of the chromophores. A comparison of the results obtained from different multilayer arrangements is suggestive of inter‐layer couplings for the case of head‐to‐head configurations of the aggregated chromophores. The results from the mixing studies reveal the evolution of two different aggregated species, one shifted hypsochromically and one shifted bathochromically from the monomer absorption and serve to quantify the relative proportions and sizes of these aggregates.
Surface functionalization and surface recognition: Plasmon optical detection of molecular recognition at self assembled monolayers
Authors: Häußling Lukas , Knoll Wolfgang , Ringsdorf Helmut , Schmitt Franz‐Josef , Yang Jianling 
Published: March 2011

AbstractThe synthesis of biotin‐ functionalized organic mercaptans and their chemisorption on gold surfaces is described. Biotin bound covalently to self assembled monolayers is recognized by streptavidin from aqueous buffer solutions. Spacer length and packing density of the biotin labels on the organic surface determine the docking kinetics. With a flexible and hydrophilic spacer very fast ‐diffusion controlled‐docking is observed. As an alternative method of self assembly the spreading of organic mercaptans on water surfaces is established. Pressure‐area diagrams of different functionalized mercaptans and disulfides are shown and their monolayer properties are discussed.
Characterisation of LB multilayers of soluble phthalocyaninatopolysiloxane
Authors: Schwiegk S. , Fischer H. , Xu Y. , Kremer F. , Wegner G. 
Published: March 2011

AbstractTetra(methoxy)tetra(octyloxy)phthalocyaninatopolysiloxane (PcPS), a soluble rigid‐rod polymer, forms stable monolayers on water, which can be transferred onto solid substrates. The orientation of the polymer in the transferred layers is induced by the flow on the water subphase. If a convergent flow is induced, the molecules will be aligned parallel to the dipping direction. A DC‐conductivity of 10−7 S · cm−1 was measured for the undoped films. Measurements with an <HG/PcPS/ITO> sandwich structure show rectification and hysteresis characteristics. PcPS modified by terminal double bonds in the side chains can be crosslinked by UV irradiation. Patterns can be developed in these films using a negative photoresist technique.
The influence of structure change on electrical properties of conducting LB films produced from hexadecyl‐TCNQ and heptadecyldimethyl‐TTF mixture
Authors: Berzina T. S. , Shikin S. A. , Troitsky V. I. , Yanusova L. G. 
Published: March 2011

AbstractConducting Langmuir‐Blodgett films of hexadecyl‐TCNQ and heptadecyl dimethyl‐TTF mixture in the ratios from 1:1 to 1:2.5 are studied. Temperature dependence of film conductivity possesses some specific features. Strong increase of conductivity and decrease of activation energy take place after annealing at 307–315 K. On the other hand, the film loses conductance after heating above 315 K. To explain this behaviour the investigations of conducting multilayers by means of electron diffraction, electron microscopy, and X‐ray small‐angle scattering were carried out. Some relations between changes of electrical properties and structural transformations are ascertained.
Ultrathin metal films and inorganic clusters via thermodesorption of LB films
Authors: Tippmann‐Krayer P. , Meisel W. , Höhne U. , Möhwald H. 
Published: March 2011

AbstractLangmuir‐Blodgett multilayers of cadmium arachidate and ferric stearate were investigated during heating in order to derive information on processes involved in thermodesorption and on the inorganic microstructures left on the substrate after thermodesorption. We studied these processes by X‐ray induced photoelectron spectroscopy (XPS), interference enhanced reflection (IeR), Nomarsky microscopy, electron microprobe analysis and in the case of Fe57‐ions by conversion electron Mössbauer spectroscopy (CEMS).Two different mechanisms of desorption were observed. In the case of cadmium arachidate multilayers it is shown that before desorption the film ruptures laterally and then forms droplets. At temperatures between 250°C and 350°C the aliphatic molecular part is desorbed and the inorganic material (Cd) remains on the surface. These threedimensional Cd‐clusters have a rather uniform lateral distribution and dimension (0.5–2μm) and normal extension larger than 1000Å. The size may be controlled via nucleation and growth kinetics.In contrast to this thermodesorption of the aliphatic chains of ferric stearate multilayers leads to a rather uniform continuous oxidic layer. By means of CEMS it could be shown that during desorption under H2‐atmosphere the iron was reduced (e.g. 40% metallic iron). The degree of oxidation can be controlled via temperature and time of reduction.
Visco‐elastic properties of thin films probed with a quartz crystal resonator
Authors: Johannsmann D. , Embs F. , Willson C. G. , Wegner G. , Knoll W. 
Published: March 2011

AbstractWe report on the visco‐elastic characterization of thin layers using a quartz crystal resonator. A parallel ellipsometric setup is used to determine optical thicknesses. A theory of thickness shear resonators covered with visco‐elastic films is presented. The glass transition of a 350 nm film of low‐molecular‐weight polystyrene can be followed. Secondary resonances in frequency shift and damping are observed, when the wavelength of transverse sound is in the same order of magnitude as its thickness. The UV‐induced desorption of poly[(bis)‐m‐butoxy‐phenyl‐silane] shows strong visco‐elastic effects, if done under oxygen atmosphere. Desorption via an oily phase consisting of medium‐size oligomers is suggested.
An electron diffraction study of deposited docosanoic acid monolayers
Authors: Steitz R. , Mitchell E. , Peterson I. R. 
Published: March 2011

AbstractDocosanoic acid monolayers deposited on thin polymer films under different water surface conditions have been investigated using transmission electron diffraction at normal and tilted incidence. Diffraction patterns obtained from the L2 and L2' phase are quite similar, but distinctly different to samples coated from the CS phase. The former were consistent with molecules perpendicular to the substrate, arranged in a texture of grains with unusual orthorhombic packing. There is evidence for a phase transition from a liquid crystalline phase on the water surface.