References of "Krüger, Jan-Kristian 30000392"
     in
Bookmark and Share    
Full Text
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)

Detailed reference viewed: 64 (5 UL)
Full Text
Peer Reviewed
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

Detailed reference viewed: 98 (0 UL)
Full Text
Peer Reviewed
See detailComment on "thermal glass transition beyond the vogel-fulcher-tammann behavior for glass forming diglycidylether of bisphenol A".
Rivera, A.; Blochowicz, T.; Porokhonskyy, V. et al

in Physical Review Letters (2005), 94(12), 129603-129604

Detailed reference viewed: 83 (1 UL)
Full Text
Peer Reviewed
See detailImaging of microwave-induced acoustic fields in LiNbO3 by high-performance Brillouin microscopy
Vincent, B.; Krüger, Jan-Kristian UL; Elmazria, Omar et al

in Journal of Physics : D Applied Physics (2005), 38(12), 2026-2030

High performance Brillouin microscopy (BM) has been used to characterize the spatial distribution of piezoelectrically induced acoustic fields excited at microwave frequencies in a LiNbO3 single crystal ... [more ▼]

High performance Brillouin microscopy (BM) has been used to characterize the spatial distribution of piezoelectrically induced acoustic fields excited at microwave frequencies in a LiNbO3 single crystal. It is demonstrated that under suitable conditions BM is able to detect microwave-induced bulk as well as surface acoustic waves. Brillouin spectroscopy is able to probe sound wave intensities of induced phonons, which are as small as those of thermal phonons. [less ▲]

Detailed reference viewed: 66 (1 UL)
Full Text
Peer Reviewed
See detailMapping of Microwave-Induced Phonons by µ-Brillouin Spectroscopy: Hypersons in ZnO on Silicon
Krüger, Jan-Kristian UL; Mainka, J.; Alnot, Patrick et al

in Journal de Physique IV (2005), 129

From the structural point of view a simple Cauchy relation is not expected to hold for isotropic materials. Such a Cauchy relation would imply the reduction of independent elastic stiffness constants for ... [more ▼]

From the structural point of view a simple Cauchy relation is not expected to hold for isotropic materials. Such a Cauchy relation would imply the reduction of independent elastic stiffness constants for the isotropic state from two to one. However, high frequency elastic data of glasses and viscous liquids show a linear transformation between the shear and the longitudinal elastic stiffness which is called a generalized Cauchy relation. It seems, that the parameters of the linear transformation are related to the global and local symmetry and/or order. Brillouin investigations on the elastic stiffness coefficients of a consolidated nano-crystalline material (CeO2) and of DGEBA/SiO2 nano-composites are used in order to elucidated the role of the discrepancy between local and global symmetry and/or order. [less ▲]

Detailed reference viewed: 52 (9 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 83 (0 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 98 (0 UL)
Full Text
Peer Reviewed
See detailDifferent glassy states, as indicated by a violation of the generalized Cauchy relation.
Krüger, Jan-Kristian UL; Britz, Th; le Coutre, A. et al

in New Journal of Physics (2003), 5(80), 1-11

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus can be measured in addition to the longitudinal modulus already well above the thermal glass ... [more ▼]

Using Brillouin spectroscopy as a probe for high-frequency clamped acoustic properties, a shear modulus can be measured in addition to the longitudinal modulus already well above the thermal glass transition. On slow cooling of the liquid through the thermal glass transition temperature Tg, both moduli show a kink-like behaviour and the function follows a generalized Cauchy relation (gCR) defined by the linear relation , which completely hides the glass transition. In this work we show experimentally that on fast cooling this linear transformation becomes violated within the glassy state, but that thermal ageing drives the elastic coefficients towards the gCR, i.e. towards a unique glassy state. [less ▲]

Detailed reference viewed: 89 (2 UL)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 65 (0 UL)
Full Text
Peer Reviewed
See detailCauchy-like relation between elastic constants in amorphous materials.
Krüger, Jan-Kristian UL; Baller, Jörg UL; Britz, Th et al

in Physical Review. B, Condensed Matter and Materials Physics (2002), 66(1), 012206-012210

It is well known that in addition to the longitudinal modulus, viscoelastic liquids show a shear stiffness at sufficiently high probe frequencies due to structural relaxations. For probe frequencies that ... [more ▼]

It is well known that in addition to the longitudinal modulus, viscoelastic liquids show a shear stiffness at sufficiently high probe frequencies due to structural relaxations. For probe frequencies that are large compared to the structural relaxation frequency, the measured elastic longitudinal and shear moduli become so-called clamped properties (c11∞ and c44∞, respectively). During freezing or polymerization of amorphous liquids, these clamped moduli behave in a strongly nonlinear fashion as a function of temperature or polymerization time. Based on Brillouin spectroscopy data we will show that there exists a linear relation between c11∞ and c44∞ over a large temperature or polymerization time range. Surprisingly, the parameters of this linear relation between the elastic moduli vary only little for different materials. Implications for the nonlinear elastic behavior at the glass transition will be discussed on the basis of mode Grüneisen parameters. [less ▲]

Detailed reference viewed: 90 (0 UL)
Full Text
Peer Reviewed
See detailFreezing of Nano-Scaled Fractal Molecules: Dendrimers
Krüger, Jan-Kristian UL; Veith, M.; Elsässer, R. et al

in Ferroelectrics (2001), 259(1-4), 27-36

Within this paper we present mono-disperse dendrimers as a new class of ideal canonical glass formers where the frustration mechanism originates from the self similar intramolecular order. Because of ... [more ▼]

Within this paper we present mono-disperse dendrimers as a new class of ideal canonical glass formers where the frustration mechanism originates from the self similar intramolecular order. Because of their fractal intramolecular structure these dendrimers are hardly able to build up a three dimensional translation symmetry necessary to form the crystalline state. Instead they show an unconventional dynamic and static freezing behavior at rather low temperatures. Based on temperature modulated differential scanning calorimetry (TMDSC) and Brillouin spectroscopy (BS) we give further evidences for the existence of an ideal primary glass transition with a thermal glass transition temperature which increases with the generation index of the fractal molecule. However, the primary glass transitions of higher generations do not completely erase the memory of the fractal intramolecular mobility but allow the survival of dynamic processes significant for the freezing of the constituting molecular unit. [less ▲]

Detailed reference viewed: 88 (0 UL)
Full Text
Peer Reviewed
See detailElastic properties of single-crystalline and consolidated nano-structured yttrium oxide at room temperature.
Baller, Jörg UL; Krüger, Jan-Kristian UL; Birringer, R. et al

in Journal of Physics : Condensed Matter (2000), 12(25), 5403-5409

High resolution Brillouin spectroscopy was used to characterize the elastic stiffness properties of consolidated nano-crystalline yttrium oxide as well as of the related single-crystalline state. Defect ... [more ▼]

High resolution Brillouin spectroscopy was used to characterize the elastic stiffness properties of consolidated nano-crystalline yttrium oxide as well as of the related single-crystalline state. Defect enriched grain boundaries are discussed as sources for the extremely soft elastic properties of the nano-crystalline state. [less ▲]

Detailed reference viewed: 67 (0 UL)
See detailSurface Induced Order in Organic and Anorganic Materials on Nano-Structured Poly-tetrafluoroethylene.
Krüger, Jan-Kristian UL; Fischer, C.; Baller, Jörg UL et al

in Frontiers in Science and Technology, Advanced Physics Studies Press (2000),7th FSRC FERROELECTRICS-2000 (2000)

Detailed reference viewed: 35 (6 UL)
Full Text
Peer Reviewed
See detailOn the Influence of Nano-Scaling on the Glass Transition of Molecular Liquids
Krüger, Jan-Kristian UL; Holtwick, R.; le Coutre, Andre et al

in Nanostructured Materials (1999), 12(1), 519-522

The nature of the glass transition is still a matter of debate. We used temperature modulated DSC (TMDSC) and Brillouin spectroscopy ( BS ) to investigate the freezing behaviour of canonical glasses ... [more ▼]

The nature of the glass transition is still a matter of debate. We used temperature modulated DSC (TMDSC) and Brillouin spectroscopy ( BS ) to investigate the freezing behaviour of canonical glasses ( salol and di-n-butyl-phtalate (DBP)) confined to controlled pore glasses (CPG) with pore diameters between 2.5 and 20 nm. The temperature behaviour of the heat capacity of the composite system deviates from the bulk fluid properties and we interpret the remaining kink-like anomaly at Tg as a static glass transition. In smaller pores Tg is only slightly shifted to lower temperatures. This operative Tg is in good agreement with sound velocity data showing a sharp kink at Tg. The working hypothesis of the existence of a static glass transition is supported by the fact that the -relaxation process disappears with decreasing pore diameter. [less ▲]

Detailed reference viewed: 74 (1 UL)
Full Text
Peer Reviewed
See detailExistence of An Intrinsic Glass Transition In A Silicon Rubber: Hypersonic Versus Calorimetric Properties
Krüger, Jan-Kristian UL; Mesquida, P.; Baller, Jörg UL

in Physical Review. B, Condensed Matter and Materials Physics (1999), 60(14), 10037-10041

Time-domain temperature-modulated differential scanning calorimetry and high-performance Brillouin spectroscopy have been used as experimental techniques in order to investigate the effect of the thermal ... [more ▼]

Time-domain temperature-modulated differential scanning calorimetry and high-performance Brillouin spectroscopy have been used as experimental techniques in order to investigate the effect of the thermal glass transition on the specific heat as well as on the acoustic properties, quantities which are intimately related by thermodynamics, but measured at completely different frequencies. Using a siloxane as a model substance, we demonstrate the efficiency of hypersonic relaxations until thermal freezing of the material. Introducing the optoacoustic dispersion function as a sensitive measure for structural relaxations, we show that the high-frequency α relaxations are truncated by the thermal glass transition instead of dying out at much higher temperatures. Moreover, the extrapolated static compliance of the rubbery state goes to zero close to but below the thermal glass transition temperature Tg, indicating the existence of an acoustic instability which is reminiscent of the so-called Kauzmann paradox. [less ▲]

Detailed reference viewed: 64 (0 UL)
Full Text
Peer Reviewed
See detailPhases and phase transitions of KPF6
Huber, P.; Krummeck, H.; Baller, Jörg UL et al

in Ferroelectrics (1997), 203(1), 211-219

Potassium hexafluorophosphate KPF6 has been investigated by X-ray powder diffraction, calorimetry and Brillouin spectroscopy. With decreasing temperature, the crystal shows a sequence of phases: NaCl-type ... [more ▼]

Potassium hexafluorophosphate KPF6 has been investigated by X-ray powder diffraction, calorimetry and Brillouin spectroscopy. With decreasing temperature, the crystal shows a sequence of phases: NaCl-type cubic-monoclinic-monoclinic with two-phase coexistence regions in between. In the cubic phase the elastic constants have been determined. c44 and c12 show a slight softening. [less ▲]

Detailed reference viewed: 126 (1 UL)
Full Text
Peer Reviewed
See detailSurface-induced organization of linear molecules on nanostructured polytetrafluoroethylene: Crystalline state of poly[vinylidenefluoride-trifluoroethylene].
Krüger, Jan-Kristian UL; Heydt, B.; Fischer, C. et al

in Physical Review. B, Condensed Matter and Materials Physics (1997), 55(6), 3497-3506

Highly crystalline and uniaxial-oriented polytetrafluoroethylene films, nanostructured in one dimension, were used to produce a fully crystalline, thermoreversible morphology in the ferroelectric ... [more ▼]

Highly crystalline and uniaxial-oriented polytetrafluoroethylene films, nanostructured in one dimension, were used to produce a fully crystalline, thermoreversible morphology in the ferroelectric copolymer poly[vinylidenefluoride-trifluoroethylene]. The resulting state is built up of regularly stacked lamellar crystals of about 100 nm thickness and lateral dimensions of about 6 μm. [less ▲]

Detailed reference viewed: 98 (1 UL)
Full Text
Peer Reviewed
See detailSecond-order elasticity of liquid crystals within their nematic state at high frequencies
Krüger, Jan-Kristian UL; Grammes, C.; Jiménez, R. et al

in Physical Review. E : Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (1995), 51(3), 2115-2128

Within this work we present Brillouin and ultrasonic investigations performed on the liquid crystals p-methoxybenzylidene p-(n-butylaniline) (MBBA), p-azoxyanisol (PAA), 4-cyano-4-n-alkylbiphenyles (nCB ... [more ▼]

Within this work we present Brillouin and ultrasonic investigations performed on the liquid crystals p-methoxybenzylidene p-(n-butylaniline) (MBBA), p-azoxyanisol (PAA), 4-cyano-4-n-alkylbiphenyles (nCB), and 4-n-pentoxybenzylidene-4'-n-octoaniline (5O.8). Special attention has been paid to the evolution of a significant splitting of the two longitudinal polarized acoustic modes within the nematic phase. Angle-resolving Brillouin spectroscopy allowed the determination of the complete stiffness tensors and hence a discussion of the propagation of quasitransverse polarized acoustic modes in the nematic state of liquid crystals. We analyze the behavior of the eigenvectors of the relevant acoustic modes and discuss their significance for the propagation of quasishear modes. For 5O.8 we report an acoustic instability within its nematic state. We confirm the existence of a universal thermal relaxation mechanism of weak activation energy for the nematic state of classical liquid crystals. The observed hypersonic anisotropy is discussed in terms of that relaxation mechanism and is compared with that of glass-forming liquid crystals. [less ▲]

Detailed reference viewed: 74 (3 UL)
Full Text
Peer Reviewed
See detailUniversal relaxation behavior of classical liquid crystals at hypersonic frequencies.
Grammes, C.; Krüger, Jan-Kristian UL; Bohn, K.-P. et al

in Physical Review. E : Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics (1995), 51

Within this work we present comparative Brillouin and ultrasonic investigations of p-methoxybenzylidene p-(n-butylaniline), p-azoxyanisol, and 4-cyano-4’-pentyl-biphenyl performed in the vicinity of the ... [more ▼]

Within this work we present comparative Brillouin and ultrasonic investigations of p-methoxybenzylidene p-(n-butylaniline), p-azoxyanisol, and 4-cyano-4’-pentyl-biphenyl performed in the vicinity of the nematic-isotropic transition. We confirm the existence of a universal hypersonic relaxation mechanism of weak activation energy and a related significant splitting of the two principal longitudinal acoustic modes within the nematic phase. Brillouin refractometry is proposed as a method to determine the magnitude of the nematic order parameter simultaneously with the second-order elastic stiffness constants. The origin of the hypersonic anisotropy is discussed in terms of thermal relaxations and the evolution of the nematic order parameter. [less ▲]

Detailed reference viewed: 86 (0 UL)