Jürgen Pionteck

Leibniz Institute of Polymer Research Dresden, Dresden, Saxony, Germany

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Publications (134)279.62 Total impact

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    ABSTRACT: The fragility parameter has been acknowledged as one of the most important characteristics of glass-forming liquids. We show that the mystery of the dramatic change in molecular dynamics of systems approaching the glass transition can be better understood by the high pressure study of fragility parameters defined in different thermodynamic conditions. We formulate and experimentally confirm a few rules obeyed by the fragility parameters, which are also rationalized by the density scaling law and its modification suggested for associated liquids. In this way, we successfully explore and gain a new insight into the pressure effect on molecular dynamics of van der Waals liquids, polymer melts, ionic liquids, and hydrogen-bonded systems near the glass transition.
    The Journal of chemical physics. 10/2014; 141(13):134507.
  • The Journal of Chemical Physics 08/2014; 141(7):079901. · 3.12 Impact Factor
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    ABSTRACT: In this work we examine, for the first time, the molar conductivity behavior of the deeply supercooled room temperature ionic liquid [C4mim][NTf2] in the temperature, pressure and volume thermodynamic space in terms of density scaling (TV(γ))(-1) combined with the equation of state (EOS). The exponent γσ determined from the Avramov model analysis is compared with the coefficient obtained from the viscosity studies carried out at moderate temperatures. Therefore, the experimental results presented herein provide the answer to the long-standing question regarding the validity of thermodynamic scaling of ionic liquids over a wide temperature range, i.e. from the normal liquid state to the glass transition point. Finally, we investigate the relationship between the dynamic and thermodynamic properties of [C4mim][NTf2] represented by scaling exponent γ and Grüneisen constant γG, respectively.
    Physical Chemistry Chemical Physics 08/2014; · 4.20 Impact Factor
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    ABSTRACT: A cyclic anhydride cured epoxy modified with carboxyl-terminated poly (butadiene-co-acrylonitrile) liquid rubber (CTBN) and SiC nanofibers was developed by two different mixing strategies. In mixing method 1, SiC nanofibers were sonicated in epoxy/CTBN mixture, while in mixing method 2 the sonicated epoxy/SiC mixture was mechanically mixed with CTBN. The effects of liquid rubber, SiC nanofiber and their mixing methods on the cure shrinkage and cure kinetics of an epoxy/nadic methyl anhydride system were studied using pressure-volume-temperature (PVT) analysis. The influence of SiC nanofiber and mixing method on cross-linking induced phase separation were investigated by means of optical microscopy. The glass transition temperature (Tg) and the thermal stability of nanocomposites were evaluated. The epoxy/SiC/CTBN nanocomposite prepared by method 2 exhibited enhanced Tg and thermal stability compared with neat epoxy and epoxy/CTBN blend. Moreover, improved impact strength was shown by epoxy/SiC/CTBN nanocomposites prepared by both methods, in comparison with epoxy/CTBN blend and epoxy/SiC nanocomposite. Additionally, fractographic analysis was carried out using scanning electron microscopy and a toughening mechanism for epoxy/SiC/CTBN nanocomposites was proposed.
    Composites Science and Technology 07/2014; 102:65-73. · 4.48 Impact Factor
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    ABSTRACT: In this Letter, we investigate how changes in the system entropy influence the characteristic time scale of the system molecular dynamics near the glass transition. Independently of any model of thermodynamic evolution of the time scale, against some previous suppositions, we show that the system entropy $S$ is not sufficient to govern the time scale defined by structural relaxation time $\tau $. In the density scaling regime, we argue that the decoupling between $\tau $ and $S$ is a consequence of different values of the scaling exponents $\gamma $ and $\gamma_S $ in the density scaling laws, $\tau = f(\rho ^\gamma /T)$ and $S = h(\rho ^{\gamma_S}/T)$, where $\rho $ and $T$ denote density and temperature, respectively. It implies that the proper relation between $\tau $ and $S$ requires supplementing with a density factor, $u(\rho)$, i.e.,$\tau = g(u(\rho )h(S))$. This meaningful finding additionally demonstrates that the density scaling idea can be successfully used to separate physically relevant contributions to the time scale of molecular dynamics near the glass transition. As an example, we revise the Avramov entropic model of the dependence $\tau (T,\rho )$, giving evidence that its entropic basis has to be extended by the density dependence of the maximal energy barrier for structural relaxation.
    06/2014;
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    ABSTRACT: Theoretical and experimental studies on the crystallization of a supercooled liquid, dimethyl phthalate, are explored in a wide range of temperatures and pressures (up to 1.8 GPa). By considering only isochronal conditions, we were able to control molecular mobility and untangle the thermodynamic effects on crystallization from kinetic ones. The analysis of experimental results revealed that crystallization of supercooled dimethyl phthalate speeds up under pressure. However, at pressures higher than ca. 1.2 GPa, a sudden change in the crystallization tendency of the investigated material was observed. Thermodynamic aspects of the crystallization process under the invariable influence of the mobility factor were described theoretically within the formalism provided by Gutzow and co-workers [Gutzow, I. et al. J. Mater. Sci. 1997, 32, 5389−5403]. The validity of the classical approach applied to express thermodynamic parameters governing the liquid/crystal phase transition under compression is carefully discussed.
    Crystal Growth & Design 04/2014; 14(5):2097–2104. · 4.69 Impact Factor
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    ABSTRACT: Multiwalled carbon nanotubes (CNT) were modified via the non-covalent approach using anodic surfactants dodecylbenzenesulfonic acid (DBSA) and poly(ethylene glycol) n-alkyl 3-sulfopropyl ether potassium salt and cationic surfactant cetyltrimethylammonium bromide (CTAB). These surfactants were used individually or as DBSA/CTAB mixtures. Surface modification was ultrasonically-assisted with a control over sonication power (64 or 360 W). The surface properties of modified CNT particles were determined by X-ray photoelectron spectroscopy and scanning electron microscopy. The electrical conductivities of unmodified CNT, particles treated by ultrasound, and CNT modified with surfactants were measured. Thermogravimetric analysis was used to determine the mass loading of surfactants after drying. The highest increase in conductivity was reached when CNT were treated solely with the anionic surfactant DBSA under the influence of soft ultrasound. This work shows conclusively that ultrasound-assisted modification of CNT by surfactants is a simple and efficient approach to prepare surface modified and highly conductive CNT, provided that physical (ultrasonic) and chemical (surfactants) treatments are concomitantly controlled. Copyright © 2014 John Wiley & Sons, Ltd.
    Surface and Interface Analysis 03/2014; · 1.39 Impact Factor
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    ABSTRACT: In this Letter we report the relation between ionic conductivity and structural relaxation in supercooled protic ionic liquids (PILs) under high pressure. The results of high-pressure dielectric and volumetric measurements, combined with rheological and temperature-modulated differential scanning calorimetry experiments, have revealed a fundamental difference between the conducting properties under isothermal and isobaric conditions for three PILs with different charge transport mechanisms (Grotthuss vs vehicle). Our findings indicate a breakdown of the fractional Stokes-Einstein relation and Walden rule when the ionic transport is controlled by fast proton hopping. Consequently, we demonstrate that the studied PILs exhibit significantly higher conductivity than one would expect taking into account that they are in fact a mixture of ionic and neutral species. Thus, the examined herein samples represent a new class of "superionic" materials desired for many advanced applications.
    Physical Review Letters 11/2013; 111(22):225703. · 7.73 Impact Factor
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    ABSTRACT: In this paper, we present dielectric studies on the effect of different thermodynamic conditions on the physical stability of van der Waals glass-forming material of pharmaceutical interest, indomethacin. By maintaining isochronal condition during measurements, we were able to control the kinetic factor of the crystallization process and untangle purely thermodynamic effects on crystallization from kinetic ones. This cannot be achieved by any other experimental attempt performed at atmospheric pressure. Along with experimental studies, crystallization of supercooled indomethacin under pressure was described theoretically. We have demonstrated within the studied pressure range (0.1–220 MPa) that one should expect an increase of thermodynamic driving force, decrease in melt/crystal interface energy, and critical nuclei size. Therefore, an experimentally observed increase in the overall crystallization rate under isochronal conditions can be exclusively rationalized as due to variations of the thermodynamic factor.
    Crystal Growth & Design 10/2013; 13(11):4648–4654. · 4.69 Impact Factor
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    ABSTRACT: The cure reaction, rheology, volume shrinkage, and thermomechanical behavior of epoxy-TiO2 nanocomposites based on diglycidyl ether of bisphenol A cured with 4,4′-diaminodiphenylsulfone have been investigated. The FTIR results show that, at the initial curing stage, TiO2 acts as a catalyst and facilitates the curing. The catalytic effect of TiO2 was further confirmed by the decrease in maximum exothermal peak temperature (DSC results); however, it was also found that the addition of TiO2 decreases the overall degree of cure, as evidenced by lower total heat of reaction of the cured composites compared to neat epoxy. The importance of cure rheology in the microstructure formation during curing was explored by using rheometry. From the PVT studies, it was found that TiO2 decreases the volume shrinkage behavior of the epoxy matrix. The mechanical properties of the cured epoxy composites, such as tensile strength, tensile modulus, flexural strength, flexural modulus, impact strength, and fracture toughness of the polymer composites, were examined. The nanocomposites exhibited good improvement in dimensional, thermal, and mechanical properties with respect to neat cross-linked epoxy system. FESEM micrographs of fractured surfaces were examined to understand the toughening mechanism.
    Journal of Polymers. 08/2013; 2013.
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    ABSTRACT: Broadband dielectric spectroscopy and pressure-temperature-volume methods are employed to investigate the effect of hydrostatic pressure on the conductivity relaxation time (τσ), both in the supercooled and glassy states of protic ionic liquid lidocaine hydrochloride monohydrate. Due to the decoupling between the ion conductivity and structural dynamics, the characteristic change in behavior of τσ(T) dependence, i.e., from Vogel-Fulcher-Tammann-like to Arrhenius-like behavior, is observed. This crossover is a manifestation of the liquid-glass transition of lidocaine HCl. The similar pattern of behavior was also found for pressure dependent isothermal measurements. However, in this case the transition from one simple volume activated law to another was noticed. Additionally, by analyzing the changes of conductivity relaxation times during isothermal densification of the sample, it was found that compression enhances the decoupling of electrical conductivity from the structural relaxation. Herein, we propose a new parameter, dlogRτ∕dP, to quantify the pressure sensitivity of the decoupling phenomenon. Finally, the temperature and volume dependence of τσ is discussed in terms of thermodynamic scaling concept.
    The Journal of Chemical Physics 05/2013; 138(20):204502. · 3.12 Impact Factor
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    ABSTRACT: In the current work, free volume concepts, primarily applied to glass formers in the literature, were transferred to ionic liquids (ILs). A series of 1-butyl-3-methylimidazolium ([C4MIM](+)) based ILs was investigated by Positron Annihilation Lifetime Spectroscopy (PALS). The phase transition and dynamic properties of the ILs [C4MIM][X] with [X](-) = [Cl](-), [BF4](-), [PF6](-), [OTf](-), [NTf2](-) and [B(hfip)4](-) were reported recently (Yu et al., Phys. Chem. Chem. Phys., 2012, 14, 6856-6868). In this subsequent work, attention was paid to the connection of the free volume from PALS (here the mean hole volume, 〈vh〉) with the molecular structure, represented by volumes derived from X-ray diffraction (XRD) data. These were the scaled molecular volume Vm,scaled and the van der Waals volume Vvdw. Linear correlations of 〈vh〉 at the "knee" temperature (〈vh〉(Tk)) with Vm,scaled and Vvdw gave good results for the [C4MIM](+) series. Further relationships between volumes from XRD data with the occupied volume Vocc determined from PALS/PVT (Pressure Volume Temperature) measurements and from Sanchez-Lacombe Equation of State (SL-EOS) fits were elaborated (Vocc(SL-EOS) ≈ 1.63 Vvdw, R(2) = 0.981 and Vocc(SL-EOS) ≈ 1.12 Vm,scaled, R(2) = 0.980). Finally, the usability of Vm,scaled was justified in terms of the Cohen-Turnbull (CT) free volume theory. Empirical CT type plots of viscosity and electrical conductivity showed a systematic increase in the critical free volume with molecular size. Such correlations allow descriptions of IL properties with the easily accessible quantity Vm,scaled within the context of the free volume.
    Physical Chemistry Chemical Physics 05/2013; · 4.20 Impact Factor
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    ABSTRACT: Poly (acrylonitrile-butadiene-styrene) (ABS) was used to modify diglycidyl ether of bisphenol-A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO2 reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS-cured epoxy/ABS/TiO2 hybrid composites systems have two Tgs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO2 particles. The addition of TiO2 induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO2 filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO2 components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO2 are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
    Journal of Applied Polymer Science 02/2013; 127(4). · 1.40 Impact Factor
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    ABSTRACT: Poly(acrylonitrile-styrene-butadiene) (ABS) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin, and the modified epoxy resin was used as the matrix for making multiwaled carbon tubes (MWCNTs) reinforced composites and were cured with diamino diphenyl sulfone (DDS) for better mechanical and thermal properties. The samples were characterized by using infrared spectroscopy, pressure volume temperature analyzer (PVT), thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), thermo mechanical analyzer (TMA), universal testing machine (UTM), and scanning electron microscopy (SEM). Infrared spectroscopy was employed to follow the curing progress in epoxy blend and hybrid composites by determining the decrease of the band intensity due to the epoxide groups. Thermal and dimensional stability was not much affected by the addition of MWCNTs. The hybrid composite induces a significant increase in both impact strength (45%) and fracture toughness (56%) of the epoxy matrix. Field emission scanning electron micrographs (FESEM) of fractured surfaces were examined to understand the tough-ening mechanism. FESEM micrographs reveal a synergetic effect of both ABS and MWCNTs on the toughness of brittle epoxy matrix.
    Journal of Applied Polymer Science 02/2013; 127(4):3093–3103. · 1.40 Impact Factor
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    ABSTRACT: Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO2 reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO2 hybrid composites systems have two Tgs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO2 particles. The addition of TiO2 induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO2 filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO2 components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO2 are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
    Journal of Applied Polymer Science 01/2013; 127(4). · 1.40 Impact Factor
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    ABSTRACT: Different amounts of multiwalled carbon tubes (MWCNTs) were incorporated into an epoxy resin based on diglycidyl ether of bisphenol A and both epoxy precursor and composite were cured with 4,4′‐diamino diphenyl sulfone. Transmission and scanning electron microscopy demonstrated that the carbon nanotubes are dispersed well in the epoxy matrix. Differential scanning calorimetry measurements confirmed the decrease in overall cure by the addition of MWCNTs. A decrease in volume shrinkage of the epoxy matrix caused by the addition of MWCNTs was observed by pressure–volume–temperature measurements. Thermomechanical and dynamic mechanical analysis were performed for the MWCNT/epoxy composites, showing that the T g was slightly affected, whereas the dimensional stability and stiffness are improved by the addition of MWCNTs. Electrical conductivity measurements of the composite samples showed that an insulator to conductor transition takes place between 0.019 and 0.037 wt % MWCNTs. The addition of MWCNTs induces an increase in both impact strength (18%) and fracture toughness (38%) of the epoxy matrix with very low filler content. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
    Journal of Applied Polymer Science 01/2013; 127(4). · 1.40 Impact Factor
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    ABSTRACT: Commercial Udel® poly(ether sulfone) (PSU) was filled with three different commercially available multiwalled carbon nanotubes (MWCNTs) by small scale melt mixing. The MWCNTs were as grown NC 7000 and two of its derivatives prepared by ball milling treatment. One of them was unmodified (NC 3150); the other was amino modified (NC 3152). The main difference beside the reactivity was the reduced aspect ratio of NC 3150 and NC 3152 caused by ball milling process. All PSU/MWCNT composites with similar filler content were prepared under fixed processing conditions and comparative analysis of their electrical and mechanical properties were performed and were correlated with their microstructure, characterized by optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). A non-uniform MWCNT dispersion was observed in all composites. The MWCNTs were present in form of agglomerates in the size of 10–60 μm whereas the deagglomerated part was homogeneously distributed in the PSU matrix. The differences in the agglomeration states correlate with the variations of properties between different PSU/MWCNT composites. The lowest electrical percolation threshold of 0.25–0.5 wt.% was observed for the shortened non-functionalized MWCNT composites and the highest for amine-modified MWCNT composites (ca. 1.5 wt.%). The tensile behavior of the three composites was only slightly altered with CNT loading as compared to the pure PSU. However, the elongation at break showed a reduction with MWCNT loading and the reduction was least for composite with best MWCNT dispersion.
    Composites Science and Technology 10/2012; 72(15):1933–1940. · 4.48 Impact Factor
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    ABSTRACT: We report that the pressure coefficient of the glass transition temperature, dT_{g}/dp, which is commonly used to determine the pressure sensitivity of the glass transition temperature T_{g}, can be predicted in the thermodynamic scaling regime. We show that the equation derived from the isochronal condition combined with the well-known scaling, TV^{γ} = const, predicts successfully values of dT_{g}/dp for a variety of glass-forming systems, including van der Waals liquids, polymers, and ionic liquids.
    Physical Review E 10/2012; 86(4-1):041502. · 2.31 Impact Factor
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    ABSTRACT: The in-situ cure and cure kinetics of an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) polymerized with an anhydride hardener and its mixtures with a liquid polybutadiene rubber having hydroxyl functionality (HTPB) were studied using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) in an isothermal mode. The cure reaction was monitored in-situ by FTIR spectroscopy by observing variation in intensity of epoxy, anhydride, and ester bands. The cure reaction mechanisms by which the network structure of epoxy was developed were discussed. Isothermal mode DSC measurements were performed at selected temperatures. The reaction followed an autocatalytic mechanism, and kinetic analysis was done by a phenomenological model developed by Kamal. Good fits were obtained between the autocatalytic model and the experimental data up to the vitrification state. Afterward, the reaction became diffusion controlled. The reaction during the later stages of cure was explained by introducing a diffusion factor, which agreed well with the kinetic data. The nature of the developing morphology of modified epoxies was analyzed by optical microscopy (OM) and small angle laser light scattering (SALLS) technique. The ultimate morphology of the cured blends was analyzed using scanning electron microscopy (SEM). The cure kinetics has been correlated with the developed morphology to get insight into the mechanism of reaction-induced microphase separation.
    Industrial & Engineering Chemistry Research 09/2012; 51(38):12178–12191. · 2.24 Impact Factor
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    ABSTRACT: A noninvasive approach is used to fabricate electronically conductive and flexible polymer fibers by fixing carbon nanotube (CNT) networks as a thin layer on thermoplastic polyurethane (TPU) multifilaments. The anchoring of the CNT layer is achieved by partially embedding or penetrating CNTs from the dispersion into the swollen multifilament surface. Thus a stable and high conductivity (up to 102 S/m at 10 wt.% CNT loading) of the resulting CNTs–TPU fibers is realized while the mechanical properties of the TPU multifilament, especially the strain to failure of >1500%, are not affected by increasing the thickness of the CNT layer. Real time analysis of the resistance of the CNTs–TPU fibers during incremental tensile loading tests reveal that the increase of resistance as a function of the strain is attributed to stretching-induced deformation, alignment, and, at high strains, destruction of the conducting network. Moreover, the changes in resistance are highly reversible under cyclic stretching up to a strain deformation of 400%.
    Carbon 09/2012; 50(11):4085–4092. · 6.16 Impact Factor

Publication Stats

662 Citations
279.62 Total Impact Points

Institutions

  • 1995–2014
    • Leibniz Institute of Polymer Research Dresden
      • Max Bergmann Center for Biomaterials
      Dresden, Saxony, Germany
  • 2010–2013
    • University of Silesia in Katowice
      • Institute of Physics
      Katowice, Silesian Voivodeship, Poland
  • 2008–2010
    • Mahatma Gandhi University
      • School of Chemical Sciences
      Kottayam, Kerala, India
  • 2003
    • Martin Luther University of Halle-Wittenberg
      • Institute of Physics
      Halle-on-the-Saale, Saxony-Anhalt, Germany
  • 1995–1999
    • Slovak Academy of Sciences
      • Polymer Institute
      Presburg, Bratislavský, Slovakia