References of "Possart, Wulff"
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See detailLaser Assisted Joining of Hybrid Polyamide-aluminum Structures
Lamberti, Christian UL; Solchenbach, Tobias UL; Plapper, Peter UL et al

in Physics Procedia (2014), 56(0), 845-853

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See detailInfluence of Nanoparticles on the Coupling Between Optical Dipoles in Epoxy-Silica Nanocomposites During Network Formation
Philipp, Martine UL; Müller, Ulrich UL; Gervais, Pierre-Colin et al

in The Journal of Adhesion (2012), 88(7), 566-588

High-performance refractometry and infrared spectroscopy are combined in order to elucidate the gelation process and the glass transition during the network formation of epoxies and epoxy-based ... [more ▼]

High-performance refractometry and infrared spectroscopy are combined in order to elucidate the gelation process and the glass transition during the network formation of epoxies and epoxy-based nanocomposites. Whereas infrared spectroscopy yields the chemical conversion due to the opening of oxirane rings during the covalent network formation, high-performance refractometry is extremely sensitive to the accompanying changes of the arrangement of the molecular network. In accordance with the Lorentz-Lorenz relationship, the evolution of the refractive index seems to reflect that of the mass density during polymerization of the epoxy-based systems within the limits of a few percent. The slight deviations from the Lorentz-Lorenz relationship, which occur during the gelation of the epoxy-based systems, are attributed to long-ranged dipole-dipole interactions, which respond at optical frequencies. This point of view is supported by the fact that chemically inert silica nanoparticles embedded in the pure epoxy matrix as disturbances for these dipole-dipole interactions are able to diminish or even to suppress totally this excess contribution of the refractive index. [less ▲]

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See detailOn the interplay between matter transport and structure formation at epoxy-hardener interfaces visualized by scanning Brillouin microscopy
Philipp, Martine UL; Müller, Ulrich UL; Sanctuary, Roland UL et al

in Soft Matter (2011), 7(1), 118-124

Structural developments are investigated in network-forming reactive polymers by time- and 10 space-resolved scanning Brillouin microscopy. Hypersonic properties are probed to reveal the subtle interplay ... [more ▼]

Structural developments are investigated in network-forming reactive polymers by time- and 10 space-resolved scanning Brillouin microscopy. Hypersonic properties are probed to reveal the subtle interplay between molecular transport, dissolution, polymerization and network defects in the vicinity of the interface between reactants, which are either pure epoxy resin or various epoxy resin-hardener mixtures, topped by a layer of pure hardener. The trans-interfacial polymerization produces heterogeneous epoxy structures of either gelatinous or glassy nature. Interestingly, the 15 hardener can easily penetrate and swell these networks and epoxy network fragments can be transported over several millimeters by convective flow. The observed features may be used to form interpenetrating networks during self-healing procedures. [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 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 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 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 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 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 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 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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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 detailMechanical Interphases in Epoxies as seen by Nondestructive High-Performance Brillouin Microscopy
Krüger, Jan-Kristian UL; Müller, Ulrich UL; Bactavatchalou, Ravindrakumar et al

in Adhesion - Current Research and Application (2005)

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See detailA Reply to the Comment by A. Rivera et al.
Krüger, Jan-Kristian UL; Britz, Thomas; Baller, Jörg UL et al

in Physical Review Letters (2005), 94

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See detailGradient of the Mechanical Modulus in Glass-Epoxy-Metal Joints as Measured by Brillouin Microscopy.
Krüger, Jan-Kristian UL; Possart, Wulff; Bactavatchalou, R. et al

in Journal of Adhesion (2004), 80(7), 585-599

The newly developed Brillouin microscopy is used for the first time to measure in situ the longitudinal elastic stiffness coefficient in the GHz-range inside of glass-epoxy-metal joints as a function of ... [more ▼]

The newly developed Brillouin microscopy is used for the first time to measure in situ the longitudinal elastic stiffness coefficient in the GHz-range inside of glass-epoxy-metal joints as a function of distance from the substrates. Interphases with a local variation of mechanical properties are quantitatively characterized. These interphases possess unexpected widths of tens to hundreds of microns. Inside the interphases, the spatial variation of the longitudinal stiffness coefficient depends on the type of substrate, on the curing conditions for the epoxy and probably on the distribution of internal stresses. The obtained spatial mechanical profiles provide valuable insight into the morphology-driven mechanics of the interphase, but additional information is needed for a full understanding of their physical and chemical origin. The presented results prove the sensitivity of the Brillouin microscopy; the elastic stiffness coefficients are detected with an accuracy in the subpercentage range. The spatial resolution is better than 10 µm. [less ▲]

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See detailAcoustic profilometry within polymers as performed by Brillouin microscopy
Sanctuary, Roland UL; Bactavatchalou, R.; Müller, Ulrich UL et al

in Journal of Physics : D Applied Physics (2003), 36(21), 2738-2742

Using high performance Brillouin spectroscopy we present a new technique, which enables us to perform acoustic microscopy with a spatial resolution of about 1 μm. This technique, called Brillouin ... [more ▼]

Using high performance Brillouin spectroscopy we present a new technique, which enables us to perform acoustic microscopy with a spatial resolution of about 1 μm. This technique, called Brillouin microscopy, is tested on several bulk- and film-like polymer samples. [less ▲]

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See detailThermal Glass Transition Beyond the Vogel-Fulcher-Tammann Behavior for Glass Forming Diglycidylether of Bisphenol A
Krüger, Jan-Kristian UL; Britz, Th; Baller, Jörg UL et al

in Physical Review Letters (2002), 89

For the low molecular weight fragile liquid diglycidyl ether of bisphenol A we report, based on Brillouin and dielectric spectroscopy, on a thermal glass transition where the relaxation time of the α ... [more ▼]

For the low molecular weight fragile liquid diglycidyl ether of bisphenol A we report, based on Brillouin and dielectric spectroscopy, on a thermal glass transition where the relaxation time of the α process does not go to infinity. Instead, the structural α relaxation disappears spontaneously at the transition point. That discontinuity in relaxation time coincides with a kink in the longitudinal hypersonic velocity and determines unambiguously the transition from the liquid to the glassy state. [less ▲]

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