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

Poster (2013, March)

Detailed reference viewed: 39 (6 UL)
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 Characterization of Amine-Epoxy Interphase in 3D Confinement network (porous glass)
Filimon, Marlena UL; Schmauch, Jörg; Sanctuary, Roland UL

Poster (2013)

Many aspects of polymer research and application are directly connected with surface and interface phenomena occurring when polymers are brought into contact with substrates made of another kind of ... [more ▼]

Many aspects of polymer research and application are directly connected with surface and interface phenomena occurring when polymers are brought into contact with substrates made of another kind of material (e.g. metals, nanoparticles, etc.). Generally, interphases emerge between polymer matrix and substrate. These are regions with morphologies and properties differing from those of polymer and substrate. While curing a thermoset, at least two different types of monomers react to form a high molecular weight polymer network. The composition of the mixture of reactance can be altered near substrate in contact with thermoset components. In this poster, we present some preliminary results obtained for interphases which appear while curing an amine-epoxy thermoset in contact with a porous glass (pore size ~20 nm). As tools for investigating the interphases, we exploited Scanning Electron Microscopy (SEM) in addition with Energy-Dispersive X-ray Spectroscopy (EDS) and Tapping-Mode Atomic Force Microscopy (TM - AFM). [less ▲]

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See detailKinetic processes at the demixing transition of PNIPAM solutions
Philipp, Martine UL; Müller, Ulrich UL; Jiménez Riobóo et al

in Soft Matter (2013), 9

Kinetic processes, which are joined with mass transport, are studied in the vicinity of the sharp LCST-type demixing transition of semi-dilute aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions ... [more ▼]

Kinetic processes, which are joined with mass transport, are studied in the vicinity of the sharp LCST-type demixing transition of semi-dilute aqueous poly(N-isopropyl acrylamide) (PNIPAM) solutions. These processes are slow as compared to the highly cooperative collapse of individual polymer chains. Purely elastic properties, that are particularly sensitive to this phase transition, are addressed depending on the temperature, space and time by Brillouin spectroscopy. Above the demixing temperature Tc, we discriminate between kinetics related to the phase separation into PNIPAM-rich and PNIPAM-poor domains and kinetics connected to the impact of gravitation on the on-going phase separation. Using shallow temperature jumps of 0.3 C, the growth of compact PNIPAM-rich agglomerates with identical gel-like mechanical consistency is provoked independently of temperature and position within the sample above Tc. Astonishingly, the transition temperature does not vary while heating or cooling the solutions across the phase transition, although the elastic properties depend strongly on space and time during the equilibration of PNIPAM concentration gradients following the re-entrance into the lowtemperature phase. [less ▲]

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See detailTemperature modulated optical refractometry: A quasi-isothermal method to determine the dynamic volume expansion coefficient
Müller, Ulrich UL; Philipp, Martine UL; Thomassey, Matthieu UL et al

in Thermochimica Acta (2013), 555

The volume expansion coefficient is a thermodynamic key parameter yielding insight into molecular cohesion and organization of condensed matter. We present here the novel experimental technique ... [more ▼]

The volume expansion coefficient is a thermodynamic key parameter yielding insight into molecular cohesion and organization of condensed matter. We present here the novel experimental technique temperature modulated optical refractometry (TMOR) to determine not only the static but also the dynamic volume expansion coefficient of transparent condensed matter of cubic or isotropic symmetry. A specialty of TMOR is its capability to measure the volume expansion coefficient under quasi-isothermal conditions. In this experimental mode TMOR is able to differentiate between static, dynamic and kinetic contributions to the volume expansion coefficient. Due to these features TMOR especially qualifies for the investigation of structural changes provoked by structural phase transitions, glass transitions and other structure-related transformations in transparent condensed matter. The scientific potential of this novel experimental technique is demonstrated by evidencing anomalies of the complex volume expansion coefficient accompanying the chemically induced glass transition occurring during the formation of a covalently cross-linked epoxy network. [less ▲]

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See detailImmense elastic nonlinearities at the demixing transition of aqueous PNIPAM solutions
Philipp, Martine UL; Müller, Ulrich UL; Aleksandrova, Ralitsa UL et al

in Soft Matter (2013), 9

Elastic nonlinearities are particularly relevant for soft materials because of their inherently small linear elasticity. Nonlinear elastic properties may even take over the leading role for the ... [more ▼]

Elastic nonlinearities are particularly relevant for soft materials because of their inherently small linear elasticity. Nonlinear elastic properties may even take over the leading role for the transformation at mechanical instabilities accompanying many phase transitions in soft matter. Because of inherent experimental difficulties, only little is known about third order (nonlinear) elastic constants within liquids, gels and polymers. Here we show that a key concept to access third order elasticity in soft materials is the determination of mode Gr¨uneisen parameters. We report the first direct observation of third order elastic constants across mechanical instabilities accompanying the liquid–liquid demixing transition of semi-dilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions. Immense elastic nonlinearities, leading to a strong strain-softening in the phase-separating PNIPAM solutions, are observed. Molecular mechanisms, which may be responsible for these immense elastic nonlinearities, are discussed. The importance of third order elastic constants in comparison to second order (linear) elastic constants in the demixing PNIPAM solutions evidences the need to focus more on the general role played by nonlinear elasticity at phase transitions within synthetic and biological liquids and gels. [less ▲]

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See detailOn the elastic nature of the demixing transition of aqueous PNIPAM solutions
Phillip, M.; Müller, Ulrich UL; Aleksandrova, Ralitsa UL et al

in Soft Matter (2012), 8

Mechanical instabilities accompanying the demixing transition of semi-dilute aqueous poly(Nisopropylacrylamide) (PNIPAM) solutions are probed for the first time with Brillouin spectroscopy, densitometry ... [more ▼]

Mechanical instabilities accompanying the demixing transition of semi-dilute aqueous poly(Nisopropylacrylamide) (PNIPAM) solutions are probed for the first time with Brillouin spectroscopy, densitometry and refractometry. The particular role of the elastic moduli and the mass density at this coil-to-globule transition followed by molecular aggregation is investigated. Even though the demixing transition of PNIPAM solutions is denoted as a volume phase transition, it turns out that this transition is governed by the elastic properties, instead of the volume properties. This is consistent with earlier findings made for the demixing transition in chemically cross-linked PNIPAM hydrogels. Above the demixing temperature, Brillouin spectroscopy discriminates compact PNIPAM-rich agglomerates with sizes larger than 200 nm. Interestingly, these agglomerates possess a sharp distribution of elastic moduli, which can be attributed without any doubt to a material with gel-like mechanical consistency. Thus the phase-separated PNIPAM-rich agglomerates are not in the glassy state. [less ▲]

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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 detailCompetition Between Chemical Network Formation and Physical Adsorption and Desorption Processes in a Silica-Filled Silicone Rubber: Calorimetry versus Refractometry Studies
Krüger, Jan-Kristian UL; Müller, Ulrich UL; Zielinski, Bartosz UL et al

in Journal of Adhesion (2012), 88(7), 649-663

Calorimetry and high-performance refractometry are applied to study the network formation and accompanying morphological changes in reactive polydimethylsiloxane systems filled with silica nanoparticles ... [more ▼]

Calorimetry and high-performance refractometry are applied to study the network formation and accompanying morphological changes in reactive polydimethylsiloxane systems filled with silica nanoparticles. Both methods give insight into the structure formation during the polymerization of silica-filled silicone nanocomposites in an impressively complementary way. It will be shown that the specific heat flow as determined by calorimetry does not allow for estimating the chemical conversion whereas the refractive index does, which results from the different perspectives of both techniques on the relevant polymerization, adsorption, and desorption processes occurring in the nanocomposites. Finally, the interphase formation in the polymeric matrix in the vicinity of the nanoparticles and the network formation within the silicone rubber are demonstrated to be strongly correlated processes. [less ▲]

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See detailScanning Brillouin Microscopy: Acoustic Microscopy at Gigahertz Frequencies
Philipp, Martine UL; Müller, Ulrich UL; Sanctuary, Roland UL et al

in Archives des Sciences Naturelles, Physiques et Mathématiques (2012), NS 46(Special volume (invited Review Article)),

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See detailDissolution, transport and reaction at a DICY/DGEBA interface
Müller, Ulrich UL; Philipp, M.; Gaukler, J. C. et al

in Journal of Adhesion (2012), 88(3), 253-276

The curing of an epoxy consisting of the solid hardener dicyandiamide (DICY) and the resin diglycidyl ether of bisphenol A (DGEBA) is studied in a system consisting of a tablet of DICY embedded in liquid ... [more ▼]

The curing of an epoxy consisting of the solid hardener dicyandiamide (DICY) and the resin diglycidyl ether of bisphenol A (DGEBA) is studied in a system consisting of a tablet of DICY embedded in liquid DGEBA. Dissolution of DICY within the liquid DGEBA in combination with the transport of dissolved DICY from the tablet border into DGEBA and the chemical reaction of both reactants is studied by scanning Brillouin microscopy and infrared spectroscopy. Scanning Brillouin microscopy demonstrates the spatial and temporal evolution of the static and dynamic hypersonic properties in the course of curing in the vicinity of the DICY tablet. Infrared spectroscopy performed on epoxy pieces extracted from the final sample at different distances from the tablet surface give information about the spatial evolution of the curing process. The results achieved by both techniques are finally combined to yield a better understanding of the curing of DICY-based epoxies, which transform upon curing from strongly heterogeneous systems towards increasingly homogeneous systems. Copyright © Taylor & Francis Group, LLC. [less ▲]

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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 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

Detailed reference viewed: 124 (16 UL)