References of "Baller, Jörg 50000565"
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See detailStrain-induced low-frequency relaxation in colloidal DGEBA/SiO2 suspensions
Dannert, Rick UL; Sanctuary, Roland UL; Thomassey, M. et al

in Rheologica Acta (2014), 53(9), 715-723

Diglycidyl ether of bisphenol A (DGEBA) is widely exploited as an epoxy resin in adhesives and coatings. In this paper, it is used as an oligomer matrix for silica-filled nanocomposites. Rheological ... [more ▼]

Diglycidyl ether of bisphenol A (DGEBA) is widely exploited as an epoxy resin in adhesives and coatings. In this paper, it is used as an oligomer matrix for silica-filled nanocomposites. Rheological measurements show that the pure matrix obeys power-law relaxation dynamics in the vicinity of the dynamic glass transition of this low-molecular-weight glass former. In the filled systems, a low-frequency relaxation appears additionally to the structural alpha-process of the matrix. Considering the nanocomposites as Newtonian hard-sphere suspensions at low angular frequencies (or high temperatures), the modified terminal regime behavior of the matrix can be linked to strain-induced perturbations of the isotropic filler distributions. While in the low-frequency regime hydrodynamic stresses relax instantaneously, the Brownian stress relaxation is viscoelastic and can be evidenced by dynamic rheological measurements. At higher angular frequencies, the alpha-process of the matrix superimposes on the Brownian stress relaxation. In particular, we were able to depict the low-frequency anomaly for concentrated, semi-dilute, and even for dilute suspensions. [less ▲]

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See detailEffect of grafted alumina nanoparticles on thermal and dynamic mechanical properties of the styrene-butadiene rubber
Sushko, Rymma UL; Baller, Jörg UL; Filimon, Marlena UL et al

Poster (2013, September)

Elastomers filled with hard nanoparticles are of great technical importance for the rubber industry. In general, fillers improve mechanical properties of polymer materials, e.g. elastic moduli, tensile ... [more ▼]

Elastomers filled with hard nanoparticles are of great technical importance for the rubber industry. In general, fillers improve mechanical properties of polymer materials, e.g. elastic moduli, tensile strength etc. The smaller the size of the particles the larger is the interface where interactions between polymer molecules and fillers can generate new properties. The aim of this contribution is to study the influence of the fillers’ surface treatment on the thermal and mechanical behavior of nanocomposites made of styrene-butadiene rubber (SBR). Three types of nanocomposites are investigated : (i) SBR-unmodified alumina, (ii) SBR – silanized alumina and (iii) SBR – alumina grafted to polymer chains. The surface-modified alumina nanoparticles were prepared using the method described in [1]. The grafting of the SBR chains to the alumina nanoparticles was realized by means of the procedures described in [2] and [3]. Temperature Modulated Differential Scanning Calorimetry (TMDSC) and Dynamic Mechanical Analysis (DMA) are well appropriated tools to investigate the thermal and dynamic glass transition behavior of the different nanocomposites, which is expected to be very sensitive to interfacial interactions between the nanoparticles and matrix molecules. TMDSC experiments reveal that all of the nanocomposites undergo a single glass transition. Thus, interphases induced by interfacial interactions do not manifest themselves by an additional glass transition unless it is hidden by the one of the matrix. Moreover, TMDSC measurements reveal that in general the glass transition temperature Tg depends in a complex manner on the concentration and surface treatment of the nanoparticles. The most important change of Tg is observed for the grafted nanocomposites: increasing the nanoparticle weight concentration beyond 4% yields an increase of Tg by 4 K. The corresponding slowing down of the molecular dynamics goes along with a significant decrease of the relaxator strength. More generally the presented results prove that, at the same filler concentration, the number of degrees of freedom freezing at the glass transition in case of un-grafted systems is practically independent on the chemical nature of the particles surface whereas it changes when there exist covalent bonds between the polymer molecules and the nanoparticles. DMA was used to probe the rheological behaviour of the nanocomposites under oscillatory shear. Isothermal frequency sweeps performed at different temperatures yield the real (G’) and imaginary (G”) parts of the complex shear modulus. Linear response regime conditions were strictly respected. The temperature-frequency equivalence principle was exploited to construct mastercurves for G’ and G” at the reference temperature T=273 K. As usual in polymers, three different behaviors were observed: the dynamic glass transition at high frequencies, the entanglement plateau at intermediary frequencies and viscoelastic “flowing” at very low frequencies. It generally appears that the filling of the SBR matrix with nanoparticles leads to an increase of the storage modulus that is more prominent in the rubbery region than in the glassy segment. While, in the low frequency regime, untreated and silanized alumina yield a mechanical behaviour that is rather near to the one of the neat SBR matrix, the grafting of elastomer molecules to the silanized fillers obviously induces a quasi-solid like response of the system. References: 1. Y.-Ch. Yang, S.-B. Jeong, B.-G. Kim, P.-R. Yoon, Powder Technology, 191, 117–121, 2009. 2. E. Passaglia, F. Donati, Polymer, 48, 35-42, 2007. 3. A. Bhattacharya, B. Misra, Prog. Polym. Sci. 29, 767–814, 2004. [less ▲]

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See detailAnomalous behaviour of SBR/Al2O3 nanocomposites at small filler concentrations
Sushko, Rymma UL; Baller, Jörg UL; Filimon, Marlena UL et al

Poster (2013, June)

Elastomers filled with hard nanoparticles are of great importance for the rubber industry. In general, the incorporation of the small particles improves the mechanical properties of polymeric materials, e ... [more ▼]

Elastomers filled with hard nanoparticles are of great importance for the rubber industry. In general, the incorporation of the small particles improves the mechanical properties of polymeric materials, e.g. elastic modulus, tensile strength etc. Nanocomposites made of poly(styrene-co-butadiene) and alumina nanoparticles (unmodified and modified with different silane coupling agents) were investigated by temperature modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA). It has been shown that the glass transition behaviour of SBR/alumina nanocomposites differs when the concentration and surface properties of the Al2O3 nanoparticles are changed. The influence of the fillers on the shear stiffness of the rubber material was also investigated. TMDSC investigations shed light on a surprising behaviour of the glass transition temperature when the nanoparticle concentration is changed: at low filler contents the quasi-static glass transition temperature Tg passes through a minimum. While further increasing the nanoparticle content Tg increases to finally saturate at high concentrations. DMA results showed a quasi-solid-like frequency-independent response of the nanocomposites in the low frequency regime with increasing of the filler concentration. [less ▲]

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See detailPolymer physics: Heterogeneties and surface dependence molecular organization
Filimon, Marlena UL; Di Giambattista, Carlo UL; Baller, Jörg UL et al

Scientific Conference (2013, May)

In this talk, we will present some studies regarding interphases and dependences of the polymer matrix/substrate. Surfaces structuring and modification of substrates plays an important role in the studies ... [more ▼]

In this talk, we will present some studies regarding interphases and dependences of the polymer matrix/substrate. Surfaces structuring and modification of substrates plays an important role in the studies of these dependences. For these goals, different modified surfaces can be used, chemically or physically. One type of surfaces used for these structures as PTFE (poly(tetrafluoroethylene)) nanoribbons on glass/Si substrate – a polymer induced alignment. It was observed that this anti-adhesive substrate can induce a oriented structure in polymer crystal structures like ε- PLC (poly(caprolactone)). Another type of modified surface structure used in our projects is chemically modified microstructures using micro-contact printing technique. Variation of the character of the surface, hydrophilic or hydrophobic, by chemical treatment leads to different molecular interactions and thus different interphases properties. The third polymer/substrate concept for interphases studies is a 3D network confinement: well-defined network as Al templates and inhomogeneous network as porous glasses. A selective penetration of the polymer system into pores or preferential adsorption effect will be discussed. Nanocomposites made of silica nanoparticles- reactive polymers and alumina nanoparticles-SBR (styrene-butadiene rubber) give unique mechanical properties due to the combination of high elasticity with high strength. Investigation of interphases using different types of modified substrate will be point out from two ways: structure resolving, mechanical, dielectrical and calorimetrical properties. Conventional microscopic techniques, such as AFM and SEM, are specific for locally investigated structures on a nanometer scale. Using these complementary microscopic techniques, we are able to distinguish different topographic information of designed substrate. Moreover, in the view of the interphases investigation, HarmoniXTM AFM is used as a mechanical property mapping technique which is able to provide quantitative mechanical characterization of stiffness, elastic modulus, adhesion and energy dissipation of a polymer surface with high lateral resolution (> 20 nm). Mechanical properties are investigated using DMTA ( dynamic mechanical thermal analyzer) and TMA (thermo-mechanical analysis) - for determining the static elastic modules of solid or solid-like sample (polymer matrix), being able to analyze and characterize bulk-like sample at lower or higher frequencies than the dispersion o polymer regime. The temperature range is 80K-500K. Modulated differentia scanning calorimetry (MDSC) is used to examine chemical and physical aspect of the studied system. The simultaneous determination of chemical reaction heat and the specific heat capacity is used to study the curing behavior of nanocomposite network. Dielectric spectroscopy (DS) is a versatile tool to investigate local molecular dynamic for a polymeric/3D confinement network or nanocomposite network. [less ▲]

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See detailThermal and mechanical properties of styrene butadiene rubber/alumina nanocomposites
Sushko, Rymma UL; Baller, Jörg UL; Sanctuary, Roland UL

Poster (2013, March)

SBR is a rubber material with high technical relevance. In order to enhance the mechanical properties of the rubber one method consists e. g. in dispersing inorganic nanoparticles in the polymer matrix ... [more ▼]

SBR is a rubber material with high technical relevance. In order to enhance the mechanical properties of the rubber one method consists e. g. in dispersing inorganic nanoparticles in the polymer matrix. By doing so, the properties of a given composite can be tuned either by changing the nanoparticle concentration or by modifying the surface properties of the fillers. Both interventions have indeed the potential to take influence on the structure and properties of the interphases emerging between the fillers and the polymer matrix. In this contribution we report on the glass transition behavior of SBR/alumina nanocomposites when the concentration and surface properties of the Al2O3 nanoparticles are changed. We also discuss the influence of the fillers on the shear stiffness of the rubber material. The samples were investigated by temperature modulated differential scanning calorimetry (TMDSC) and dynamic mechanical analysis (DMA). TMDSC investigations shed light on a surprising behavior of the glass transition temperature when the nanoparticle concentration is changed: at low filler contents the quasi-static glass transition temperature Tg passes through a minimum. While further increasing the nanoparticle content Tg increases to finally saturate at high concentrations. One of the main DMA results is that increasing of the Al2O3 concentration induces a quasi-solid-like frequency-independent response of the nanocomposites in the low frequency regime. [less ▲]

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See detailNanoscale confinement of a low molecular weight liquid
Djemour, Anna UL; Baller, Jörg UL; Di Giambattista, Carlo UL et al

Poster (2013, March)

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See detailThermal and chemical glass transition of thermosets in the presence of two types of inorganic nanoparticles
Baller, Jörg UL; Thomassey, Matthieu UL; Ziehmer, Markus UL et al

in Thermoplastic and thermosetting polymers and composites (2011)

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See detailInfluence of crystallite size and temperature on the antiferromagnetic helices of terbium and holmium metal
Michels, Andreas UL; Bick, Jens-Peter UL; Birringer, R. et al

in Physical Review. B, Condensed Matter and Materials Physics (2011), 83

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See detailThe catalytic influence of alumina nanoparticles on epoxy curing
Baller, Jörg UL; Thomassey, Matthieu UL; Ziehmer, Markus UL et al

in Thermochimica Acta (2011), 517

The curing process of diepoxide-triamine systems filled with water and untreated alumina nanoparticles has been investigated. The influence of both types of fillers on the curing process is very similar ... [more ▼]

The curing process of diepoxide-triamine systems filled with water and untreated alumina nanoparticles has been investigated. The influence of both types of fillers on the curing process is very similar. This is reflected by a similar shape of the heat flow (HF) and specific heat capacity curves during curing. A catalytic effect of hydroxyl groups in the water and on the nanoparticles surfaces is made responsible for the observed curing behaviour. It turns out that the strength of the catalytic effect depends on the type of filler. The described influence of alumina nanoparticles on thermoset curing is looked upon as being representative for nanocomposites consisting of epoxy thermosets and metal oxide nanoparticles without surface treatment. [less ▲]

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See detailInteractions between silica nanoparticles and an epoxy resin before and during network formation.
Baller, Jörg UL; Becker, Nora UL; Ziehmer, Markus UL et al

in Polymer (2009), 50(14), 3211-3219

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica ... [more ▼]

In polymer nanocomposites, interactions between filler particles and matrix material play a crucial role for their macroscopic properties. Nanocomposites consisting of varying amounts of silica nanoparticles and an epoxy resin based on diglycidyl ether of bisphenol A (DGEBA) have been studied before and during network formation (curing). Rheology and mainly temperature modulated differential scanning calorimetry (TMDSC) have been used to investigate interactions between the silica nanoparticles and molecules of the epoxy oligomer or molecules of the growing epoxy network. Measurements of the complex specific heat capacity before curing showed that interactions between the nanoparticles and DGEBA molecules are very weak. An expression for an effective specific heat capacity of the silica nanoparticles could be deduced. Examination of the isothermal curing process after addition of an amine hardener yielded evidences for a restricted molecular mobility of the reactants in the cause of network formation. These restrictions could be overcome by increasing the curing temperature. No evidences for an incorporation of the silica nanoparticles into the epoxy network, i.e. for a strong chemical bonding to the network, were found. Interactions between the silica nanoparticles and the epoxy resins under study are assumed to be of a physical nature at all stages of network formation. [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 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 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 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 ▲]

Detailed reference viewed: 82 (2 UL)