References of "Baller, Jörg 50000565"
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See detailIsotropic–isotropic phase separation and spinodal decomposition in liquid crystal–solvent mixtures
Reyes, Catherine UL; Baller, Jörg UL; Araki, Takeaki et al

in Soft Matter (2019), 15

Phase separation in mixtures forming liquid crystal (LC) phases is an important yet under- appreciated phenomenon that can drastically influence the behaviour of a multi-component LC. Here we demonstrate ... [more ▼]

Phase separation in mixtures forming liquid crystal (LC) phases is an important yet under- appreciated phenomenon that can drastically influence the behaviour of a multi-component LC. Here we demonstrate, using polarising microscopy with active cooling as well as differential scanning calorimetry, that the phase diagram for mixtures of the LC-forming compound 4’-n- pentylbiphenyl-4-carbonitrile (5CB) with ethanol is surprisingly complex. Binary mixtures reveal a broad miscibility gap that leads to phase separation between two distinct isotropic phases via spinodal decomposition or nucleation and growth. On further cooling the nematic phase enters on the 5CB-rich side, adding to the complexity. Significantly, water contamination dramatically raises the temperature range of the miscibility gap, bringing up the critical temperature for spinodal de- composition from ∼ 2◦C for the anhydrous case to > 50◦C if just 3 vol.% water is added to the ethanol. We support the experiments with a theoretical treatment that qualitatively reproduces the phase diagrams as well as the transition dynamics, with and without water. Our study highlights the impact of phase separation in LC-forming mixtures, spanning from equilibrium coexistence of multiple liquid phases to non-equilibrium effects due to persistent spatial concentration gradients. [less ▲]

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See detailFractionation of cellulose nanocrystals: enhancing liquid crystal ordering without promoting gelation
Honorato Rios, Camila UL; Lehr, Claudius Moritz UL; Schütz, Christina UL et al

in NPG asia materials (2018)

Colloids of electrically charged nanorods can spontaneously develop a fluid yet ordered liquid crystal phase, but this ordering competes with a tendency to form a gel of percolating rods. The threshold ... [more ▼]

Colloids of electrically charged nanorods can spontaneously develop a fluid yet ordered liquid crystal phase, but this ordering competes with a tendency to form a gel of percolating rods. The threshold for ordering is reduced by increasing the rod aspect ratio, but the percolation threshold is also reduced with this change; hence, prediction of the outcome is nontrivial. Here, we show that by establishing the phase behavior of suspensions of cellulose nanocrystals(CNCs) fractionated according to length, an increased aspect ratio can strongly favor liquid crystallinity without necessarily influencing gelation. Gelation is instead triggered by increasing the counterion concentration until theCNCs lose colloidal stability, triggering linear aggregation, which promotes percolation regardless of the original rod aspect ratio. Our results shine new light on the competition between liquid crystal formation and gelation in nanoparticle suspensions and provide a path for enhanced control of CNC self-organization for applications in photonic crystal paper or advanced composites. [less ▲]

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See detailRelaxations in the metastable rotator phase of n-eicosane
Di Giambattista, Carlo UL; Sanctuary, Roland UL; Perigo, Elio Alberto UL et al

in The Journal of Chemical Physics (2015), 143

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See detailSlow dynamics in sheared DGEBA/SiO2 suspensions
Dannert, Rick UL; Sanctuary, Roland UL; Baller, Jörg UL

Presentation (2015, March)

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See detailUnexpected flow and relaxation behaviour of a low molecular weight glass former
Baller, Jörg UL

Presentation (2015, January 22)

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See detailMobility restrictions and glass transition behaviour of an epoxy resin under confinement
Djemour, A.; Sanctuary, Roland UL; Baller, Jörg UL

in Soft Matter (2015), 11(13), 2683-2690

Confinement can have a big influence on the dynamics of glass formers in the vicinity of the glass transition. Already 40 to 50 K above the glass transition temperature, thermal equilibration of glass ... [more ▼]

Confinement can have a big influence on the dynamics of glass formers in the vicinity of the glass transition. Already 40 to 50 K above the glass transition temperature, thermal equilibration of glass formers can be strongly influenced by the confining substrate. We investigate the linear thermal expansion and the specific heat capacity c(p) of an epoxy resin (diglycidyl ether of bisphenol A, DGEBA) in a temperature interval of 120 K around the glass transition temperature. The epoxy resin is filled into controlled pore glasses with pore diameters between 4 and 111 nm. Since DGEBA can form H-bonds with silica surfaces, we also investigate the influence of surface silanization of the porous substrates. In untreated substrates a core/shell structure of the epoxy resin can be identified. The glass transition behaviours of the bulk phase and that of the shell phase are different. In silanized substrates, the shell phase disappears. At a temperature well above the glass transition, a second transition is found for the bulk phase - both in the linear expansion data as well as in the specific heat capacity. The c(p) data do not allow excluding the glass transition of a third phase as being the cause for this transition, whereas the linear expansion data do so. The additional transition temperature is interpreted as a separation between two regimes: above this temperature, macroscopic flow of the bulk phase inside the porous structure is possible to balance the mismatch of thermal expansion coefficients between DGEBA and the substrate. Below the transition temperature, this degree of freedom is hindered by geometrical constraints of the porous substrates. Moreover, this second transition could also be found in the linear expansion data of the shell phase. [less ▲]

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See detailAnomalous glass transition behavior of SBR–Al2O3 nanocomposites at small filler concentrations
Sushko, Rymma UL; Filimon, Marlena UL; Dannert, Rick UL et al

in Nanotechnology (2014), 25(42), 425704

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. Using temperature-modulated differential scanning calorimetry and dynamic mechanical analysis, we investigated the properties of pure styrene-butadiene rubber (SBR) and SBR/alumina nanoparticles. Beside a reinforcement effect seen in the complex elastic moduli, small amounts of nanoparticles of about 2 wt% interestingly lead to an acceleration of the relaxation modes responsible for the thermal glass transition. This leads to a minimum in the glass transition temperature as a function of nanoparticle content in the vicinity of this critical concentration. The frequency dependent elastic moduli are used to discuss the possible reduction of the entanglement of rubber molecules as one cause for this unexpected behavior. [less ▲]

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See detailComparative study of the effect of untreated, silanized and 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

in AIP Conferences Proceedings (2014, May 15), 1599

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. Using Temperature Modulated Differential Scanning Calorimetry (TMDSC) and Dynamic Mechanical Analysis (DMA), we investigated the properties of the pure styrene-butadiene rubber (SBR), SBR/ alumina nanoparticles, SBR/silanized alumina and SBR/alumina grafted to polymer chains. Beside a general reinforcement effect seen in the complex elastic moduli, the studies revealed that: i) small concentrations of nanoparticles (of 1.5-2 wt%) lead to a minimum in the glass transition temperature as a function of nanoparticle content; ii) for the grafted nanocomposites increasing the nanoparticle concentration beyond 4 wt% yields an increase of Tg by 4 K; iii) DMA mastercurves showed that in case of untreated and silanized alumina mechanical behaviour of the composite systems is rather near to the one of the SBR matrix, but the grafting of elastomer molecules to the silanized fillers induces a quasi-solid like response of the system in the low frequency regime. [less ▲]

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See detailAnomaly in thermal and mechanical properties of SBR/alumina nanocomposites
Sushko, Rymma UL; Baller, Jörg UL; Filimon, Marlena UL et al

Scientific Conference (2014, April 03)

Filling elastomers with nanoparticles generally leads to changes in the relaxation behavior of the matrix molecules. Using dynamic mechanical analysis (DMA) and temperature modulated calorimetry (TMDSC ... [more ▼]

Filling elastomers with nanoparticles generally leads to changes in the relaxation behavior of the matrix molecules. Using dynamic mechanical analysis (DMA) and temperature modulated calorimetry (TMDSC), we investigate the influence of different amounts of untreated, hydrophilic alumina nanoparticles on the properties of a model rubber system (SBR). Beside a reinforcement effect seen in the complex elastic moduli, small amounts of nanoparticles of about 2 wt% interestingly lead to an acceleration of the relaxation modes responsible for the thermal glass transition. This leads to a minimum in the glass transition temperature as a function of nanoparticle content in the vicinity of this critical concentration. The frequency dependent elastic moduli are used to discuss the possible reduction of the entanglement of rubber molecules as one cause for this unexpected behavior. [less ▲]

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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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