bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic conduction in cryolite‐alumina melts
Authors: Haarberg G.M. , Thonstad J. , Egan J.J. , Oblakowski R. , Pietrzyk S. 
Published: July 2012

AbstractPrevious work by the authors has shown that electrons are an important constituent of cryolite melts saturated with alumina and in contact with aluminum. This has a negative effect on the current efficiency of aluminum production in industrial cells.In the present paper, methods used to measure electronic conduction, electron mobilities, and electron concentrations in cryolite alumina melts (NaF/AlF3 molar ratio=3) will be reviewed. New results will then be reported on electronic conduction in melts with a NaF/AlF3 molar ratio of 2.4 at various sodium activities. In particular, a ratio nearer to that used in industrial cells was examined. AC resistance measurements were performed on cryolite‐based alumina melts equilibrated with aluminum‐silver alloys between 967 and 1037°C.The results were used to estimate the effect of electrons on current efficiency in cells used for the production of aluminum. Equations for the current efficiency formerly used by the authors are reviewed and calculations based on the new results are presented. In general, current efficiencies between 94.5% and 99% were obtained.
The In‐Sn‐Zn system
Authors: Xie Y. , Schicketanz H. , Mikula A. 
Published: July 2012

AbstractDTA measurements, lattice parameter investigations and micro‐probe analyses were performed on fourty ternary In‐Sn‐Zn alloys to determine the phase diagram. The investigations were carried out along three cross‐sections with a constant Sn to Zn ratio of 2:1, 1:1 and 1:2. A vertical section with 10 at% In was also measured. Based on this data as well as thermodynamic and phase diagram data of the three binary systems from literature the ternary phase diagram was optimised by using different models.Since some of these alloys might be a useful candidate for lead free solder materials the temperature dependence of the thermo‐emf was measured for some compositions.
Aerogels: Production, modification and applications
Authors: Burger T. , Fricke J. 
Published: July 2012

AbstractAerogels are highly porous, nanostructured sol‐gel derived materials. In the nineteen sixties and seventies highly transparent and monolithic silica aerogels have mainly been used in Cherenkov detectors to determine the momentum of relativistic particles. After an increasing availability of granular SiO2‐aerogels from a BASF pilot plant in the eighties, applications of these materials in solar architecture (especially for daylighting purposes and transparent thermal insulations) have been investigated. Today, additionally research focuses on metalloxide‐, organic‐ and carbon‐aerogels. The applications range from acoustic impedance matching layers in ultrasonic transducers to subtrates for catalytic materials, transparent molds for melt casting, sensors, electrodes in supercapacitors and fuel cells as well as capture of cosmic dust and micrometeorits. Particularly interesting with respect to mass applications is the use of aerogel powder in the evacuated superinsulation of the BMW latent heat storage device which can be employed to defrost the windshield or to preheat the engine. A broad availability of cheap aerogels is expected from a production process based on subcritical drying (versus supercritical extraction in an autoclave) currently persued by Hoechst AG.
Reversible molecular adsorption as a tool to observe freezing and to perform design of heteropolymer gels
Authors: Tanaka Toyoichi , Enoki Takashi , Grosberg Alexander YU. , Masamune Satoru , Oya Taro , Takaoka Yukikazu , Tanaka Kazunori , Wang Changnan , Wang Guoqiang 
Published: July 2012

AbstractProtein folding is one of the most challenging problems in science. How can polymers memorize and fold into unique conformations? How can they recognize molecules, catalyze chemical reactions, transfer molecular information, and create motions! The principle behind these mechanisms lies in the concept of thernodynamically stable phases of heteropolymers. Recent theories predict that the collapsed phase should be further classified into three phases: freely fluctuating like liquid, frozen in degenerate conformations, and frozen in a unique conformation. This yields a clue on how one can attempt creation artificial polymers capable to mimic some of the protein properties and functions. The reversible adsorption of target molecules is suggested as a primary means to achieve this goal. Target molecules with multiple adsorption sites play a twofold role. First, they mediate specific interactions between monomers and thus serve as “gluons”. Second, monitoring the adsorption provides the experimental possibility to test directly on monomer contacts, which is directly related to observation of the order parameter associated with heteropolymer freezing transition. A slight change in the backbone conformation alters the spacial arrangement of the group, allowing for reversible adsorption and release. Polymer gels are developed that can reversibly change their affinity to target molecules by orders of magnitude. The gels are made of copolymers of backbone monomers that can reorganize themselves through thermal volume phase transition and of monomers that can attract the target at multiple contact points. Further the gels “imprinted” with the target showed a marked increase in the affinity, thus mimicing a protein‐like ability to memorize and recognize certain target.
Polymer gel template for porous TiO2 production
Authors: Caruso R. A. , Giersig M. , Willig F. , Antonietti M. 
Published: July 2012

AbstractPorous networks of titanium dioxide have been produced using polymer gels as templates. Titanium dioxide is well known for its semiconductor and catalysis properties, and for being a very stable material. The porous polymer gels are produced in aqueous surfactant solutions. Following cleaning and solvent exchange procedures the titanium precursor can be incorporated within the gel and hydrolysed. The organic material is removed during calcination leaving the structured titanium dioxide. Both the rutile and anatase forms of titanium dioxide can be produced. The resulting crystal structure and the surface area of the oxide are important for determining its scope of application. These properties have been studied using electron microscopy, X‐ray diffraction and gas sorption.
Influence of surfactant on the gelation of novel ethylene glycol esters of silicic acid
Authors: Sattler K. , Gradzielski M. , Mortensen K. , Hoffmann H. 
Published: July 2012

AbstractThe sol‐gel transition of a novel glycol ester of ortho silicic acid is investigated by small angle neutron scattering technique. We measured the changes of scattering intensity as a function of time during gelation and show the formation of a fractal structure.When we mix our ester with an aqueous surfactant solution no precipitate is formed as observed in common template synthesis of mesoporous materials. Because of the water solubility of our silicate precursor it can be dissolved into the surfactant phase without phase separation. During hydrolysis of the precursor ethylene glycol is produced which does not affect the hydrophobic interaction of the surfactant.It is shown by contrast variation that surfactant does not affect the fractal dimension of the final silica gel. Measurements after gelation demonstrate the unchanged presence of surfactant micelles.
Monomeric encapsulation of phthalocyanine‐dye molecules in the pores of Si‐MCM‐41 and Ti‐MCM‐41
Authors: Wark M. , Ortlam A. , Ganschow M. , Schulz‐Ekloff G. , Wöhrle D. 
Published: July 2012

AbstractTitanium species and substituted or unsubstituted zinc phthalocyanine (ZnPc) complexes exhibiting negative, positive or no charges are incorporated in mesoporous MCM‐41 materials by (i) hydrothermal synthesis in the presence of hexadecyltrimethylammonium chloride as surfactant and (ii) impregnation of pre‐synthesized calcined Si‐MCM‐41.The ordering of the hexagonal MCM‐41 structures is revealed from X‐ray diffractograms and nitrogen adsorption isotherms. The dispersion and the coordination of the Ti in the walls or in the pores is deduced from UV/Vis diffuse reflectance spectra (DR‐UV/Vis). The amount of Ti built into the walls of the MCM‐41 under maintenance of a perfect hexagonal structure is restricted to about 2 wt.‐%. In the pores up to 8 wt.‐% Ti can be fixed a silanol groups under molecular, i.e. non‐aggregated, dispersion.The degree of dispersion of ZnPc is concluded from the analysis of the Q‐band structure in the DR‐UV/Vis spectra. Predominantly non‐aggregated ZnPcs in a monomeric state can be obtained, (i) if the ZnPC is incorporated in the micellar structure of the surfactant molecules by adding it to the synthesis gel of the MCM‐41 or (ii) if the ZnPc is adsorbed to Ti‐MCM‐41 with Ti species in high dispersion in the pores. A tight contact between the donor ZnPc and the acceptor titanium oxide, enables an electron transfer and a quenching of the fluorescence of the dye.
Spectroscopic investigations of the entrapment of hematoporphyrin IX in sol‐gel prepared silica and silica/titania gels and monoliths
Authors: Krüger J. M. , Breuer H. D. 
Published: July 2012

AbstractBy using the sol‐gel process, free base porphyrin doped silica and silica/titania, gels, monoliths, and glasses, with up to 20 wt.% titania, have been synthesised. The monoliths were characterised by BET isotherms, X‐Ray spectroscopy, and AFM spectroscopy. Absorption and fluorescence spectroscopic measurements indicate that, in Si and Si/Ti‐monoliths an equilibrium between the free base hematoporphyrin IX and its dicationic form exists. By additionally doping of pyrene as a donor dye, the energy transfer to hematoporphyrin IX as acceptor was investigated. Stem‐Volmer quenching of the fluorescence of pyrene was found in monoliths.
An EXAFS study on thiolcapped CdTe nanocrystals
Authors: Rockenberger Jörg , Tröger Larc , Rogach Andrey L. , Tischer Markus , Grundmann Marius , Weller Horst , Eychmüller Alexander 
Published: July 2012

AbstractTemperature dependent EXAFS measurements have been carried out on 2‐mercaptoethanol‐stabilized CdTe nanocrystals. The technique allows to study the structural and dynamic properties of the CdTe core and the Cd‐SR (R = organic rest) shell separately. Based on the coordination numbers and the Cd/Te‐ratio determined by EXAFS, the formula [Cd54 Te32(SCH2CH2OH)52]8− is suggested. The underlying structure is a tetrahedral CdTe core (zincblende) partially coated by a Cd‐SR surface layer.
Fluorescence spectroscopical investigation of the gelation of sterical stabilised titanium dioxide sols
Authors: Krüger J. M. , Breuer H. D. 
Published: July 2012

AbstractThe gelation of TiO2‐sols, prepared by sol‐gel process, can be monitored by adding polyethylene glycol as polymer (sterical stabilisation). The forming of the inorganic TiO2 network was examined by using the microprobe technique. Pyrene was doped in TiO2‐sols and its characteristic fluorescence spectroscopic changes were investigated during the gelation. The vibrational fine structure of its emission spectrum changes and the ratio I3/I1 was determined and compared with homogenous solvents. By pulse fluorimetric measurements two different lifetimes of pyrene in TiO2‐sols were found.
X‐ray diffraction study of CCl4 crystallisation in vycor and silica gel mesopores
Authors: Schäfer Bernd , Langel Walter 
Published: July 2012

AbstractThe crystallisation of CCl4 in the mesopores of Vycor glass and silica gel has been studied by X‐ray powder diffraction. For the phase transitions from the liquid to the high temperature phase Ib and from Ib to the low temperature phase II undercooling is observed. At low temperatures the pore crystallites in Vycor have a coherence length of about 120 Å, which corresponds well to the pore chord distribution. Heating up from 67 K induces recrystallisation at about 180 K. The resulting crystallites of 500 Å in diameter show the phase transitions to the Ib phase and to the liquid at the bulk temperatures. We attribute this effect, which had not been seen before, to irreversible increase of the molecular order during cooling. The highly ordered phase attained at 67 K is thermodynamically unstable at 180 K and recrystallises. — In addition to Bragg reflections intense diffuse scattering is observed indicating amorphous zones with coherence lengths of the order of 11‐18 Å. We assign this to a surface layer whose structure is perturbed due to the interaction with the fractal Vycor surface.
Antiferroelectric gels
Authors: Strauss J. , Kitzerow H.‐S. 
Published: July 2012

AbstractWe have investigated the electro‐optic properties of a gel consisting of an antiferroelectric liquid crystalline (AFLC) mixture and an anisotropic polymer network, formed by photopolymerization of a mesogenic monomer. Like the pure AFLC mixture, the gel exhibits the well‐known tristable electro‐optical switching but with a decreased slope of the electro‐optic response curve, thus making gray‐scales available. In addition, the spontaneous polarization and the switching angle are reduced by the polymer network, whereas the switching times are independent of the polymer concentration. Applying a simple model, we found that the polymer network primarily changes the anchoring conditions of the liquid crystal.
Surface effects accompanying the Lα‐to‐L+α transition of the amphiphile C12E4 in water as studied by Neutron reflectivity
Authors: Steitz R. , Braun Chr. , Bowers J. , Lang P. , Findenegg G. H. 
Published: July 2012

AbstractThe interface of a concentrated solution of the amphiphile C12E4 in D2O against a hydrophobic‐coated silicon wafer has been studied near the congruent transition from the isotropic phase L1 to the lamellar phase Lα in a temperature range from 20 to 44°C by neutron reflectometry. The measurements reveal that the Lα phase — which is stable only in a narrow temperature range (20.6‐20.9°C at the chosen composition of 29 wt‐% C12E4 in D2O) ‐ couples strongly to the solid substrate, i.e. adjacent lamellae exhibit strong lateral correlation and are oriented parallel to the surface of the substrate. As the temperature is increased the sample transforms to a phase L+α which is stable from 20.9°C up to the highest experimental temperature. Unlike Lα, the Lα+ phase exhibits a broad Bragg peak in the reflectivity curve, indicating weak lateral correlation of adjacent lamellae. Furthermore, rocking scans reveal no significant coupling of the layers to the substrate surface. This finding is consistent with a disordered multilayered structure of the Lα+ phase suggested by other authors.
Molecular dynamics simulation of tracer diffusion of acetonitril in polyacrylamide hydrogels
Authors: Oldiges Christian , Tönsing Thorsten , Netz Paulo , Eimer Wolfgang 
Published: July 2012

AbstractThe diffusional motion of individual acetonitril molecules in polyacrylamide hydrogels has been investigated by molecular dynamics simulation. The mobility and the reorientation of the probe particles depend on their location within the polymer network. It can be separated between slow bound molecules and faster unbound molecules. To uncover the change in diffusion mechanism, we have followed the motion of individual probe molecules. Strong polymer‐solute interactions, which are dominated by hydrogen bonding, result in a significant retardation of the transport properties. In the solvent‐rich pores of the polymer matrix the acetonitril molecules can move freely as in pure water. A comparison of calculated diffusion coefficients reveals good agreement of the MD simulation results with experimental data.
Dynamics during thermoreversible gelation of the polysaccharide schizophyllan
Authors: Richtering Walter , Fuchs Tania , Burchard Walther 
Published: July 2012

AbstractThe β‐1.3/1.6 glucan schizophyllan is a fungal polysaccharid that is known to suppress tumor growth. Addition of sorbitol to aqueous solutions of schizophyllan led to a thermoreversible formation of optically transparent gels. The gelation process was followed by low amplitude oscillatory shear as well as by static and dynamic light scattering. Power law behavior of storage modulus G′(ω) and loss modulus G″(ω) was found at the gel temperature with an exponent n = 0.5. However, no power law was found for the time correlation functions as measured by dynamic light scattering. Two separated relaxation modes were found above and below the gel transition. The slow mode diverged below the gel temperature indicating a second critical point related to heterogeneities in the gel.
Birefringence and rubber‐elastic properties of crosslinked polymers in uniaxial deformation
Authors: Rennar Nikolaus 
Published: July 2012

AbstractMeasurements of birefringence and stress on well characterized endlinked PDMS, randomly crosslinked NR/IR elastomers, and polyether networks are reported in both uniaxial extension and compression. The experimental results are compared with predictions from modern theoretical concepts.The reduced birefringence and the reduced stress are found to be dependent on the inverse deformation ratio 1/λ with a slight increase of both properties when going from extension to compression. Nevertheless, birefringence and stress seem to have the same dependence on extension respectively compression resulting in a stress‐optical coefficient (SOC) independent of the type and the amount of uniaxial deformation in the range 1.5>λ>0.7 according to the classical Kuhn‐Grün theory. Furthermore, the stress‐optical coefficients of endlinked PDMS and randomly crosslinked NR/IR networks in the unswollen state are constant over a wide range of crosslink densities and junction functionalities.A detailed analysis of the birefringence data and the mechanical properties completed by the results of swelling tests indicates a considerable contribution of topological interactions (trapped entanglements) in a certain range of crosslink densities. This contribution seems to depend on the actual conditions of the network formation. The consistency of the above conclusions is supported by transversal 1H‐NMR relaxation experiments on the crosslinked samples.
Defined photo‐crosslinking and viscometric data I: Crosslinking via phenylindene and stilbazolium chromophors
Authors: Schinner Robert , Wolff Thomas , Kuckling Dirk 
Published: July 2012

AbstractThe photochemical formation of crosslinks between polymer chains leading to networks was studied in chloroform solution of polystyrene and in aqueous solution of poly‐N‐isopropylacrylamide. The former polymer was substituted with phenylindene, the latter with stilbazolium moieties. Both of which are chromophors crosslinkable via photodimerization. Depending on polymer concentration and chromophor content the polystyrene system in chloroform formed networks upon irradiation as revealed by increased viscosity and by the appearance of viscoelasticity. Up to three stress relaxation processes were indicated by rheological analysis of relaxation curves in viscoelastic solutions. In contrast, the poly‐N‐isopropylacrylamide system showed Newtonian flow throughout with moderate viscosity increase upon irradiation. This indicated that links were formed within separate polymer coils only.
Kinetic studies in liquid and gelated water/triblock copolymers mixtures
Authors: Knoll H. , Gille K. 
Published: July 2012

AbstractRate constants of the thermal cis‐trans isomerization of an azo dye in triblock copolymer (PEO‐PPO‐PEO)/water mixtures were determined by means of conventional flash photolysis. The rate constants change characteristically on micelle formation upon increasing the temperature. Moreover they indicate that the microenvironment of the dye molecules in the water/PEO interface layers of concentrated micellar solutions does not change significantly on gelation.
Electronic structures and nature of host excitation in borates
Authors: Mishra K. C. , Deboer B. G. , Schmidt P. C. , Osterloh I. , Stephan M. , Eyert V. , Johnson K. H. 
Published: July 2012

AbstractWe report the electronic structures of three large band gap borates β‐BaB2O4, YBO3 and LuBO3, and corresponding binary oxides BaO, Y2O3, Lu2O3 and B2O3. The main objective of this investigation is to explore how the electronic structures of complex oxides relates to their binary oxides, and how tightly bound anionic groups lead to large gap oxides. The calculated electronic structures lead to good agreement between observed optical gap and structure of the valence band for these oxides. While the borates lead to large gap materials, the excitations across the band gap do not always involve bonding and antibonding states of borate groups that are common to all the ternary oxides considered in this work. Although the top of the valence band is characterized by hybridized O 2p‐ and B 2p‐like states, the bottom of the conduction band can be due to metallic states. The presence of such states near the bottom of the conduction band was speculated earlier from the excitation properties of YBO3. We have also explored the possibility of designing a multi‐photon phosphor through core valence luminescence from a ternary oxide of Ba.
Viscous fingering at the liquid/liquid interface between two coexisting phases of mixtures with a miscibility gap
Authors: Wolf H. , Woermann D. 
Published: July 2012

AbstractThe influence of the viscosity contrast factor A [( = η“‐η′)/(η“+η), η, shear viscosity: (′)(”), indices of the coexisting phases; η“>η′]on the formation of viscous fingers at a mechanically unstable liquid/liquid interface of mixtures with a miscibility gap in a narrow rectangular glass cell (closed Hele‐Shaw cell) is studied. The systems used for the experiments are: (a) 2‐butoxyethanol (C4E1)/water mixtures of critical composition. They are studied in the vicinity of the lower critical point at temperatures above the critical temperature [1.05 < (η”η') < 2.0, corresponding to 0.05<A<0.4]. A is varied by changing the temperature of the mixture; (b) poly(ethylene glycol) (PEG)/dextran (D)/water mixtures at different compositions in the vicinity of the plait point at constant temperature [10<(η“/η')<40, corresponding to 0.762<A<0.950]. The liquid/liquid interfacial tension of both systems is small (σ<0.1 mN m−1). The experimental results are analysed in terms of theoretical work of Tryggvason and Aref (J. Fluid. Mech. 177, 207 (1985)). The viscous fingering process is treated as a two‐dimensional viscous flow. For small values of A (<0.12; system (C4El1/water) the growth rates of the viscous fingers in the upward and downward direction have about the same value and the fingers have a similar shape. At larger values of A (>0.3) the fingers formed by the phase with the higher viscosity advance faster into the phase with the lower viscosity than the fingers advancing in the opposite direction. This effect is pronounced in the system PEG/D/water for which A has large values (A>0.75). In this system the viscous fingers formed by the phase with the higher viscosity are long and narrow whereas that formed by the low viscosity phase are short and broad. The temperature dependence of the mean distance <l> between viscous fingers of the system C4E1/water advancing in opposite directions approaches the theoretically expected dependence at temperature differences (Tp‐Tc)>l K corresponding to a ratio (λmax/b) > 3 (λmax, wave length of fasted growing interfacial instability; b, width of the glass cell). The experiments show that the preferential wetting of the glass walls of the Hele‐Shaw cell by one of the coexisting liquid phases leads to a three‐dimensional shape of the viscous fingers.