References of "Krüger, Jan-Kristian 30000392"
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See detailBrillouin spectroscopy applied to the characterization of SAW propagation losses in langasite
Vincent, Brice; Aubert, Thierry; Elmazria, Omar et al

in Abstract book of 2010 IEEE International Ultrasonics Symposium (2010)

High performance Brillouin microscopy has been used in order to directly measure the propagation losses of surface acoustic wave in Langasite substrate. The interdigital transducers (IDTs) were designed ... [more ▼]

High performance Brillouin microscopy has been used in order to directly measure the propagation losses of surface acoustic wave in Langasite substrate. The interdigital transducers (IDTs) were designed to generate several harmonics leading to induce acoustic waves with different wavelengths. The induced phonons were detected and characterized at different frequencies and at different distance from IDTs leading to precisely determine the propagation losses for all the excited frequencies 681, 1267 and 1463 MHz. [less ▲]

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See detailShelf Life and Controlled Cure of Epoxies by Loaded Zeolite
Gaukler, J. Ch; Müller, Ulrich UL; Krüger, Jan-Kristian UL et al

in Composite Interfaces (2010)

Epoxy formulations based on the multi-functional amine hardener, dicyandiamide (Dicy), regularly contain a free accelerator for reducing the curing temperature and the time needed to complete the network ... [more ▼]

Epoxy formulations based on the multi-functional amine hardener, dicyandiamide (Dicy), regularly contain a free accelerator for reducing the curing temperature and the time needed to complete the network formation. Unfortunately, all accelerators reduce the shelf life of these adhesives at 25◦C. In order to solve this problem, accelerator-loaded zeolites fillers were developed, optimised with respect to host–guest interactions and characterised by Fraunhofer IFAM (Bremen, Germany) with regard to the release and curing behaviour in epoxy adhesive formulations. They are added to an epoxy adhesive (diglycidylether of bisphenol A (EP) and dicyandiamide (Dicy), mass ratio 100:6.7), stored at 25◦C in regular air or cured (heated with β = 10 K/min to 170◦C subsequent isothermal curing for 45 min). That shelf life and curing behaviour are investigated by FT-IR spectroscopy and modulated DSC. Compared to the EP containing free accelerator, the zeolite-filled EP possesses a threefold increase in shelf life at 25◦C due to the immobilization of the accelerator in the pores of the zeolites. While the free accelerator acts steadily during heating, it is shown that the loaded zeolite releases the accelerator at about 76◦C. Surprisingly, the released accelerator is not only involved in the chemical formation of the epoxy network but it accelerates the dissolution of Dicy considerably. As the result, network formation at 170◦C finishes after not more than 19 min and the starting temperature for curing could be reduced to 140◦C. [less ▲]

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See detailTrans-Interfacial Polymerization and Matter Transport Processes in Epoxy-Alumina Nanocomposites Visualized By Scanning Brillouin Microscopy
Sanctuary, Roland UL; Philipp, Martine UL; Kieffer, J. et al

in Journal of Physical Chemistry B (2010), 114(25), 8396-8404

The structural developments in the vicinity of the interface between the reactants of an epoxy are investigated using time- and space-resolved scanning Brillouin microscopy. The hypersonic profile across ... [more ▼]

The structural developments in the vicinity of the interface between the reactants of an epoxy are investigated using time- and space-resolved scanning Brillouin microscopy. The hypersonic profile across the phase boundary evolves with strong spatial asymmetry and exhibits erratic behavior within the resin-rich region, which is attributed to a complex interplay between matter transport, dissolution, polymerization, and molecular unravelling process. The presence of alumina nanoparticles in the resin changes the character of these matter transport and reaction processes significantly. On the one hand, the nanoparticles act as transport barriers, hindering the mixing of the reactive components; on the other hand they seem to have a catalytic influence on the epoxy polymerization under certain circumstances. Their transport against gravity is tentatively attributed to gradients in surface tension. [less ▲]

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See detailCombination of high performance refractometry and infrared spectroscopy as a probe for chemically induced gelation and vitrification of epoxies
Müller, Ulrich UL; Philipp, Martine UL; Gervais, P. C. UL et al

in New Journal of Physics (2010), 12

A combination of infrared spectroscopy and high performance refractometry was used to investigate the chemically induced sol-gel and glass transition during the polymerization of epoxies. Representations ... [more ▼]

A combination of infrared spectroscopy and high performance refractometry was used to investigate the chemically induced sol-gel and glass transition during the polymerization of epoxies. Representations of the refractive index versus chemical conversion reveal an interesting insight in the optical properties accompanying gelation and vitrification. Whereas the electronic polarizability of the liquid state of small average molecular mass and the glassy state is dominated by the mass density, an unexpected excess polarizability observed during the gelation is attributed to cooperative dipole-dipole interactions. [less ▲]

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See detailSpace and time resolving molecular acoustics as a tool to visualize epoxy formation at a planar hardener-resin interface
Sanctuary, Roland UL; Philipp, Martine UL; Müller, Ulrich UL et al

in Chemical Physics Letters (2009), 476(1-3), 11-14

Scanning Brillouin microscopy visualizes the temporal evolution of a heterogeneous hypersonic profile during chemical reactions and transport processes around a planar phase boundary between an epoxy ... [more ▼]

Scanning Brillouin microscopy visualizes the temporal evolution of a heterogeneous hypersonic profile during chemical reactions and transport processes around a planar phase boundary between an epoxy resin and hardener. The hypersonic investigations are interpreted in terms of structural formation and annihilation in the layered sample and are compared to results obtained for a well mixed bulk sample of the same composition of reactants. Chaotic transport channels are made responsible for the creation of local glassy heterogeneities not observable in the bulk material on a macroscopic level. [less ▲]

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See detailSecond order elasticity at hypersonic frequencies of reactive polyurethanes as seen by generalized Cauchy relations.
Philipp, Martine UL; Vergnat, Christelle; Müller, Ulrich UL et al

in Journal of Physics : Condensed Matter (2009), 21

The non-equilibrium process of polymerization of reactive polymers can be accompanied by transition phenomena like gelation or the chemical glass transition. The sensitivity of the mechanical properties ... [more ▼]

The non-equilibrium process of polymerization of reactive polymers can be accompanied by transition phenomena like gelation or the chemical glass transition. The sensitivity of the mechanical properties at hypersonic frequencies—including the generalized Cauchy relation—to these transition phenomena is studied for three different polyurethanes using Brillouin spectroscopy. As for epoxies, the generalized Cauchy relation surprisingly holds true for the non-equilibrium polymerization process and for the temperature dependence of polyurethanes. Neither the sol–gel transition nor the chemical and thermal glass transitions are visible in the representation of the generalized Cauchy relation. Taking into account the new results and combining them with general considerations about the elastic properties of the isotropic state, an improved physical foundation of the generalized Cauchy relation is proposed. [less ▲]

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See detailConcentration and temperature dependence of the refractive index of ethanol-water mixtures: Influence of intermolecular interactions.
Jiménez Riobóo, R.; Philipp, Martine UL; Ramos, M. et al

in European Physical Journal E -- Soft Matter (2009), 30(1), 19-26

The temperature and concentration dependence of the refractive index, n D(x, T) , in ethanol-water mixtures agrees with previous data in the ethanol-rich concentration range. The refractive index versus ... [more ▼]

The temperature and concentration dependence of the refractive index, n D(x, T) , in ethanol-water mixtures agrees with previous data in the ethanol-rich concentration range. The refractive index versus concentration x determined at 20 ° C shows the expected maximum at about 41 mol% water (22 mass% water). The temperature derivative of the refractive index, dn D /dT, shows anomalies at lower water concentrations at about 10 mol% water but no anomaly at 41 mol% water. Both anomalies are related to intermolecular interactions, the one in nD seems to be due to molecular segregation and cluster formation while the origin of the second one in dn D /dT is still not clear. [less ▲]

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See detailEvidence for structural transformations in polymer melts
Krüger, Jan-Kristian UL; Peetz, L.; Wildner, W. et al

in Polymer (2009), 21(6), 620-626

Crystallizing and non-crystallizing polymers have been investigated by Brillouin spectroscopy in the liquid state. The temperature gradient of the sound velocity of crystallizing polymers shows a ... [more ▼]

Crystallizing and non-crystallizing polymers have been investigated by Brillouin spectroscopy in the liquid state. The temperature gradient of the sound velocity of crystallizing polymers shows a discontinuity at ~60-110K above the melting transition. The non-crystallizing polymers investigated show no uniform behaviour. We interpret the phase between the melt temperature and the temperature of the additional transformation as a phase of locally nematic structure. This interpretation is also supported by a study of density, refractive index, viscosity and hypersonic attenuation. [less ▲]

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See detailInfluence of Al2O3 nanoparticles on the isothermal cure of an epoxy resin
Sanctuary, Roland UL; Krüger, Jan-Kristian UL; Baller, Jörg UL et al

in Journal of Physics : Condensed Matter (2009), 21

The influence of Al2O3 nanoparticles on the curing of an epoxy thermoset based on diglycidyl ether of bisphenol A was investigated using temperature-modulated differential scanning calorimetry (TMDSC) and ... [more ▼]

The influence of Al2O3 nanoparticles on the curing of an epoxy thermoset based on diglycidyl ether of bisphenol A was investigated using temperature-modulated differential scanning calorimetry (TMDSC) and rheology. Diethylene triamine was used as a hardener. TMDSC not only allows for a systematic study of the kinetics of cure but simultaneously gives access to the evolution of the specific heat capacities of the thermosets. The technique thus provides insight into the glass transition behaviour of the nanocomposites and hence makes it possible to shed some light on the interaction between the nanoparticles and the polymer matrix. The Al2O3 fillers are shown to accelerate the growth of macromolecules upon isothermal curing. Several mechanisms which possibly could be responsible for the acceleration are described. As a result of the faster network growth chemical vitrification occurs at earlier times in the filled thermosets and the specific reaction heat decreases with increasing nanoparticle concentration. Rheologic measurements of the zero-shear viscosity confirm the faster growth of the macromolecules in the presence of the nanoparticles. [less ▲]

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See detailMixing Behavior and Interphase Formation in the Diethylene Triamine-Water System Studied by Optical Imaging and Spatially Resolved Brillouin Scattering
Philipp, Martine UL; Collette, Florimond; Veith, Michael et al

in Journal of Physical Chemistry B (2009), 113(38), 12655-12662

The injection of water beneath liquid diethylene triamine in a glass cuvette leads to an unexpected phase evolution behavior of the two liquids. The space and time dependent developments of the molecular ... [more ▼]

The injection of water beneath liquid diethylene triamine in a glass cuvette leads to an unexpected phase evolution behavior of the two liquids. The space and time dependent developments of the molecular structure and the underlying transport associated with mixing of the two liquids are monitored by optical imaging and scanning Brillouin microscopy. Apparently, results obtained by either experimental technique lead to disparate interpretations. Whereas optical imaging suggests the existence of a two phase structure, which disappears within a few hours, acoustic microscopy indicates the evolution of a more gradually evolving and longer-lived three phase structure. According to molecular acoustics, the transport of diethylene triamine into water and vice versa behaves strongly asymmetric in time. An attempt is made to reconcile the observed optical and acoustic manifestations of the mixing process on the basis of molecular complex formation. [less ▲]

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See detailInterphases, gelation, vitrication, porous glasses and the generalized Cauchy relation: epoxy/silica nanocomposites
Philipp, Martine UL; Müller, Ulrich UL; Jiménez Riobóo, R. J. et al

in New Journal of Physics (2009), 11(2), 023015

The generalized Cauchy relation (gCR) of epoxy/silica nanocomposites does not show either the chemically induced sol–gel transition or the chemically induced glass transition in the course of ... [more ▼]

The generalized Cauchy relation (gCR) of epoxy/silica nanocomposites does not show either the chemically induced sol–gel transition or the chemically induced glass transition in the course of polymerization. Astonishingly, by varying the silica nanoparticles’ concentration between 0 and 25 vol%in the composites, the Cauchy parameter A of the gCR remains universal and can be determined from the pure epoxy’s elastic moduli. Air-filled porous silica glasses are considered as models for percolated silica particles. A longitudinal modulus versus density representation evidences the aforementioned transition phenomena during polymerization of the epoxy/silica nanocomposites. The existence of optically and mechanically relevant interphases is discussed. [less ▲]

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See detailAcoustic Profilometry Of Interphases In An Epoxy Due To Segregation and Diffusion Using Brillouin Microscopy.
Müller, Ulrich UL; Bactavatchalou, R.; Baller, Jörg UL et al

in New Journal of Physics (2008), 10(2), 023-031

Reactive network forming polymer systems like epoxies are of huge technological interest because of their adhesive properties based on specific interactions with a large variety of materials. These ... [more ▼]

Reactive network forming polymer systems like epoxies are of huge technological interest because of their adhesive properties based on specific interactions with a large variety of materials. These specific interactions alter the morphology of the epoxy within areas determined by the correlation length of these interactions. The changed morphology leads to interphases with altered (mechanical) properties. Besides these surface-induced interphases, bulk interphases do occur due to segregation, crystallization, diffusion, etc. A new experimental technique to characterize such mechanical interphases is μ-Brillouin spectroscopy (μ-BS). With μ-BS, we studied interphases and their formation in epoxies due to segregation of the constituent components and due to selective diffusion of one component. In the latter case, we will demonstrate the influence of changing the boundary conditions of the diffusion process on the shape of the interphase. [less ▲]

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See detailOrganization versus frustration: low temperature transitions in a gelatine-based gel
Philipp, Martine UL; Müller, Ulrich UL; Sanctuary, Roland UL et al

in New Journal of Physics (2008), 10

A commercial physical gel composed of gelatine, water and glycerol shows a sol–gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not ... [more ▼]

A commercial physical gel composed of gelatine, water and glycerol shows a sol–gel transition which has been resolved by optical rotation measurements by step-wise heating the gel. This transition is not observable in the longitudinal acoustic mode measured at hypersonic frequencies with Brillouin spectroscopy. Depending on the thermal treatment of the investigated material during the sol–gel transition and within the gel state, Brillouin spectroscopy reflects tremendously different hypersonic dynamics. These distinct dynamics are responsible for the formation of different glassy states at low temperatures including that of a glass-ceramic. The large variety of super-cooled and glassy states is attributed to distinct distributions of the gel's constituents within the samples. Surprisingly, the same gel state can be produced either by annealing the gel over months or by the non-equilibrium effect of thermo-diffusion (Soret effect) in the course of some minutes. [less ▲]

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See detailChemically induced transition phenomena in polyurethanes as seen from generalized mode Grüneisen parameters.
Müller, Ulrich UL; Philipp, Martine UL; Bactavatchalou, R. et al

in Journal of Physics : Condensed Matter (2008), 20(20), 205101-205108

Many phenomenological properties of reactive polymers like polyurethanes increase or decrease continuously in the course of the curing process before saturating at the end of the chemical reaction. This ... [more ▼]

Many phenomenological properties of reactive polymers like polyurethanes increase or decrease continuously in the course of the curing process before saturating at the end of the chemical reaction. This holds true for instance for the mass density, the refractive index, the chemical turnover and the hypersonic properties. The reason for this monotone behaviour is that the chemical reaction behaves like a continuous succession of irreversible phase transitions. These transitions are superposed by the sol–gel transition and possibly by the chemically induced glass transition, with the drawback that the latter two highlighted transitions are often hidden by the underlying curing process. In this work we propose generalized mode Grüneisen parameters as an alternative probe for elucidating the polymerization process itself and the closely related transition phenomena. As a model system we use polyurethane composed of a diisocyanate and varying ratios of difunctional and trifunctional alcohols. [less ▲]

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See detailFrom the Dynamically Nanostructured Liquid to the Glassy State: A Phenomenological Approach
Krüger, Jan-Kristian UL; Petersson, J.; Baller, Jörg UL et al

E-print/Working paper (2008)

Based on experimental evidences we present a phenomenological description of the thermal glass transition as a dynamical phase transition. Different susceptibilities calculated on the basis of this ... [more ▼]

Based on experimental evidences we present a phenomenological description of the thermal glass transition as a dynamical phase transition. Different susceptibilities calculated on the basis of this description are in good qualitative agreement with experimental data. As an essential feature this novel view of the glass transition reflects the kinetic as well as the transition aspect of the thermal glass transition. [less ▲]

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See detailEffect of mixing sequence on the curing of amine-hardened epoxy/alumina nanocomposites as assessed by optical refractometry
Philipp, Martine UL; Gervais, Pierre-Colin; Sanctuary, Roland UL et al

in eXPRESS Polymer Letters (2008), 2(8), 546-552

High performance refractometry has been proven to be a useful tool to elucidate the isothermal curing process of nanocomposites. As a model system an amine-hardening epoxy filled with non-surface-treated ... [more ▼]

High performance refractometry has been proven to be a useful tool to elucidate the isothermal curing process of nanocomposites. As a model system an amine-hardening epoxy filled with non-surface-treated alumina nanoparticles was selected. The tremendous resolution of this experimental technique is used to study morphological changes within nanocomposites via the refractive index. It is shown that these morphological changes are not simply due to the curing process but also depend on the sequence of mixing the nanoparticles either first into the resin or first into the hardener. Independent of the resin/hardener composition, the type of the mixing sequence discriminates systematically between two distinct refractive index curves produced by the curing process. The difference between the two refractive index curves increases monotonically with curing time, which underlines the importance of the initial molecular environment of the nanoparticles. [less ▲]

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See detailTemperature modulated Differential Scanning Calorimetry: The Dynamic Aspect of the Specific Heat Capacity and its Relation to Entropy Production
Philipp, Martine UL; Sanctuary, Roland UL; Baller, Jörg UL et al

in Beiträge zur Experimentalphysik, Didaktik und computergestützten Physik (2007)

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See detailAbout the nature of the structural glass transtion: an experimental approach
Krüger, Jan-Kristian UL; Alnot, Patrick; Baller, Jörg UL et al

in Henkel, M.; Pleimling, M.; Sanctuary, Roland (Eds.) Aging of the Glass Transition (2007)

The nature of the glassy state and of the glass transition of structural glasses is still a matter of debate. This debate stems predominantly from the kinetic features of the thermal glass transition ... [more ▼]

The nature of the glassy state and of the glass transition of structural glasses is still a matter of debate. This debate stems predominantly from the kinetic features of the thermal glass transition. However the glass transition has at least two faces: the kinetic one which becomes apparent in the regime of low relaxation frequencies and a static one observed in static or frequency-clamped linear and non-linear susceptibilities. New results concerning the so-called ?-relaxation process show that the historical view of an unavoidable cross-over of this relaxation time with the experimental time scale is probably wrong and support instead the existence of an intrinsic glass transition. In order to prove this, three different experimental strategies have been applied: studying the glass transition at extremely long time scales, the investigation of properties which are not sensitive to the kinetics of the glass transition and studying glass transitions which do not depend at all on a forced external time scale. [less ▲]

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See detailComplex specific heat capacity of two nanocomposite systems
Sanctuary, Roland UL; Baller, Jörg UL; Krüger, Jan-Kristian UL et al

in Thermochimica Acta (2006), 445(2), 111-115

Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The ... [more ▼]

Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The properties of nanocomposites may vary between those of a simple mixture of independent components and those of a system, where specific interfacial interactions between the constituting parts lead to ‘new’ properties. Depending on the type of the nanoparticles filled into the matrix, the resulting properties might be closer to one or to the other extreme. We used temperature modulated differential scanning calorimetry (TMDSC) to investigate a matrix of the oligomer diglycidyl ether of bisphenol A (DGEBA) filled either with SiO2- or Al2O3-nanoparticles. The dependence of the complex specific heat capacity () on the concentration of nanoparticles shows a clear difference between the two systems as far as the glass transition of the oligomer is concerned. The SiO2 composite seems to behave more like a simple mixture, whereas the Al2O3 composite shows ‘new’ properties. [less ▲]

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See detailThe generalized Cauchy relation: a probe for local structure in materials with isotropic symmetry.
Bactavatchalou, R.; Alnot, Patrick; Baller, Jörg UL et al

in Journal of Physics. Conference Series (2006), 40

The elastic properties of the isotropic state of condensed matter are given by the elastic constants ell and c44. In the liquid state the static shear stiffness c44 vanishes whereas at sufficient high ... [more ▼]

The elastic properties of the isotropic state of condensed matter are given by the elastic constants ell and c44. In the liquid state the static shear stiffness c44 vanishes whereas at sufficient high probe frequencies a dynamic shear stiffness may appear. In that latter case the question about the existence of a Cauchy relation appears. It will be shown that a pure Cauchy relation can appear only under special conditions which are rarely fulfilled. For all investigated materials, including ceramics, liquids and glasses, a linear relation between ell and c44 called generalized Cauchy relation is observed, which, surprisingly, follows a linear transformation. [less ▲]

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