@article{WallerBraunHojdisetal.2007, author = {Waller, Mark P. and Braun, Heiko and Hojdis, Nils and B{\"u}hl, Michael}, title = {Geometries of Second-Row Transition-Metal Complexes from Density-Functional Theory}, series = {Journal of Chemical Theory and Computation}, volume = {3}, journal = {Journal of Chemical Theory and Computation}, number = {6}, issn = {1549-9626}, doi = {10.1021/ct700178y}, pages = {2234 -- 2242}, year = {2007}, language = {en} } @article{SvaneborgKarimiVarzanehHojdisetal.2016, author = {Svaneborg, Carsten and Karimi-Varzaneh, Hossein Ali and Hojdis, Nils and Fleck, Franz and Everaers, Ralf}, title = {Multiscale approach to equilibrating model polymer melts}, series = {Physical Review E}, volume = {94}, journal = {Physical Review E}, number = {032502}, publisher = {AIP Publishing}, address = {Melville, NY}, issn = {2470-0053}, doi = {10.1103/PhysRevE.94.032502}, year = {2016}, abstract = {We present an effective and simple multiscale method for equilibrating Kremer Grest model polymer melts of varying stiffness. In our approach, we progressively equilibrate the melt structure above the tube scale, inside the tube and finally at the monomeric scale. We make use of models designed to be computationally effective at each scale. Density fluctuations in the melt structure above the tube scale are minimized through a Monte Carlo simulated annealing of a lattice polymer model. Subsequently the melt structure below the tube scale is equilibrated via the Rouse dynamics of a force-capped Kremer-Grest model that allows chains to partially interpenetrate. Finally the Kremer-Grest force field is introduced to freeze the topological state and enforce correct monomer packing. We generate 15 melts of 500 chains of 10.000 beads for varying chain stiffness as well as a number of melts with 1.000 chains of 15.000 monomers. To validate the equilibration process we study the time evolution of bulk, collective, and single-chain observables at the monomeric, mesoscopic, and macroscopic length scales. Extension of the present method to longer, branched, or polydisperse chains, and/or larger system sizes is straightforward.}, language = {en} } @article{SvaneborgKarimiVarzanehHojdisetal.2018, author = {Svaneborg, Carsten and Karimi-Varzaneh, Hossein Ali and Hojdis, Nils and Fleck, Franz and Everaers, Ralf}, title = {Kremer-Grest Models for Universal Properties of Specific Common Polymer Species}, series = {Soft Condensed Matter}, journal = {Soft Condensed Matter}, number = {1606.05008}, year = {2018}, abstract = {The Kremer-Grest (KG) bead-spring model is a near standard in Molecular Dynamic simulations of generic polymer properties. It owes its popularity to its computational efficiency, rather than its ability to represent specific polymer species and conditions. Here we investigate how to adapt the model to match the universal properties of a wide range of chemical polymers species. For this purpose we vary a single parameter originally introduced by Faller and M{\"u}ller-Plathe, the chain stiffness. Examples include polystyrene, polyethylene, polypropylene, cis-polyisoprene, polydimethylsiloxane, polyethyleneoxide and styrene-butadiene rubber. We do this by matching the number of Kuhn segments per chain and the number of Kuhn segments per cubic Kuhn volume for the polymer species and for the Kremer-Grest model. We also derive mapping relations for converting KG model units back to physical units, in particular we obtain the entanglement time for the KG model as function of stiffness allowing for a time mapping. To test these relations, we generate large equilibrated well entangled polymer melts, and measure the entanglement moduli using a static primitive-path analysis of the entangled melt structure as well as by simulations of step-strain deformation of the model melts. The obtained moduli for our model polymer melts are in good agreement with the experimentally expected moduli.}, language = {en} } @article{SchwabHojdisLacayoetal.2016, author = {Schwab, Lukas and Hojdis, Nils and Lacayo, Jorge and Wilhelm, Manfred}, title = {Fourier-Transform Rheology of Unvulcanized, Carbon Black Filled Styrene Butadiene Rubber}, series = {Macromolecular Materials and Engineering}, volume = {301}, journal = {Macromolecular Materials and Engineering}, number = {4}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1439-2054}, doi = {10.1002/mame.201500356}, pages = {457 -- 468}, year = {2016}, abstract = {Rubber materials filled with reinforcing fillers display nonlinear rheological behavior at small strain amplitudes below γ0 < 0.1. Nevertheless, rheological data are analyzed mostly in terms of linear parameters, such as shear moduli (G′, G″), which loose their physical meaning in the nonlinear regime. In this work styrene butadiene rubber filled with carbon black (CB) under large amplitude oscillatory shear (LAOS) is analyzed in terms of the nonlinear parameter I3/1. Three different CB grades are used and the filler load is varied between 0 and 70 phr. It is found that I3/1(φ) is most sensitive to changes of the total accessible filler surface area at low strain amplitudes (γ0 = 0.32). The addition of up to 70 phr CB leads to an increase of I3/1(φ) by a factor of more than ten. The influence of the measurement temperature on I3/1 is pronounced for CB levels above the percolation threshold.}, language = {en} } @article{SchmidtTurgutLeetal.2020, author = {Schmidt, Aaron C. and Turgut, Hatice and Le, Dao and Beloqui, Ana and Delaittre, Guillaume}, title = {Making the best of it: nitroxide-mediated polymerization of methacrylates via the copolymerization approach with functional styrenics}, series = {Polymer Chemistry}, volume = {11}, journal = {Polymer Chemistry}, number = {2}, publisher = {Royal Society of Chemistry (RSC)}, address = {Cambridge}, doi = {10.1039/C9PY01458F}, pages = {593 -- 604}, year = {2020}, abstract = {The SG1-mediated solution polymerization of methyl methacrylate (MMA) and oligo(ethylene glycol) methacrylate (OEGMA, Mₙ = 300 g mol⁻¹) in the presence of a small amount of functional/reactive styrenic comonomer is investigated. Moieties such as pentafluorophenyl ester, triphenylphosphine, azide, pentafluorophenyl, halide, and pyridine are considered. A comonomer fraction as low as 5 mol\% typically results in a controlled/living behavior, at least up to 50\% conversion. Chain extensions with styrene for both systems were successfully performed. Variation of physical properties such as refractive index (for MMA) and phase transition temperature (for OEGMA) were evaluated by comparing to 100\% pure homopolymers. The introduction of an activated ester styrene derivative in the polymerization of OEGMA allows for the synthesis of reactive and hydrophilic polymer brushes with defined thickness. Finally, using the example of pentafluorostyrene as controlling comonomer, it is demonstrated that functional PMMA-b-PS are able to maintain a phase separation ability, as evidenced by the formation of nanostructured thin films.}, language = {en} } @article{MeyerHentschkeHageretal.2017, author = {Meyer, Jan and Hentschke, Reinhard and Hager, Jonathan and Hojdis, Nils and Karimi-Varzaneh, Hossein Ali}, title = {Molecular Simulation of Viscous Dissipation due to Cyclic Deformation of a Silica-Silica Contact in Filled Rubber}, series = {Macromolecules}, volume = {50}, journal = {Macromolecules}, number = {17}, issn = {1520-5835}, doi = {10.1021/acs.macromol.7b00947}, pages = {6679 -- 6689}, year = {2017}, language = {en} } @article{MayerHentschkeHageretal.2017, author = {Mayer, Jan and Hentschke, Reinhard and Hager, Jonathan and Hojdis, Nils and Karimi-Varnaneh, Hossein Ali}, title = {A Nano-Mechanical Instability as Primary Contribution to Rolling Resistance}, series = {Scientific Reports}, volume = {7}, journal = {Scientific Reports}, number = {Article number 11275}, publisher = {Springer}, address = {Berlin}, issn = {2045-2322}, year = {2017}, language = {en} } @article{HentschkeHagerHojdis2014, author = {Hentschke, Reinhard and Hager, Jonathan and Hojdis, Nils}, title = {Molecular Modeling Approach to the Prediction of Mechanical Properties of Silica-Reinforced Rubbers}, series = {Journal of Applied Polymer Science}, volume = {131}, journal = {Journal of Applied Polymer Science}, number = {18}, publisher = {Wiley}, address = {New York, NY}, issn = {1097-4628}, doi = {10.1002/app.40806}, pages = {1 -- 9}, year = {2014}, abstract = {Recently, we have suggested a nanomechanical model for dissipative loss in filled elastomer networks in the context of the Payne effect. The mechanism is based on a total interfiller particle force exhibiting an intermittent loop, due to the combination of short-range repulsion and dispersion forces with a long-range elastic attraction. The sum of these forces leads, under external strain, to a spontaneous instability of "bonds" between the aggregates in a filler network and attendant energy dissipation. Here, we use molecular dynamics simulations to obtain chemically realistic forces between surface modified silica particles. The latter are combined with the above model to estimate the loss modulus and the low strain storage modulus in elastomers containing the aforementioned filler-compatibilizer systems. The model is compared to experimental dynamic moduli of silica filled rubbers. We find good agreement between the model predictions and the experiments as function of the compatibilizer's molecular structure and its bulk concentration.}, language = {en} } @article{HeinzeMangPopescuetal.2016, author = {Heinze, D. and Mang, Thomas and Popescu, C. and Weichold, O.}, title = {Effect of side chain length and degree of polymerization on the decomposition and crystallization behaviour of chlorinated poly(vinyl ester) oligomers}, series = {Thermochimica Acta}, volume = {637}, journal = {Thermochimica Acta}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0040-6031 (electronic)}, doi = {10.1016/j.tca.2016.05.015}, pages = {143 -- 153}, year = {2016}, abstract = {Four members of a homologous series of chlorinated poly(vinyl ester) oligomers CCl₃-(CH₂CH (OCO(CH₂)ₘCH₃))ₙ-Cl with degrees of polymerization of 10 and 20 were prepared by telomerisation using carbon tetrachloride. The number of side chain carbon atoms ranges from 2 (poly(vinyl acetate) to 18 (poly(vinyl stearate)). The effect of the n-alkyl side chain length and of the degree of polymerization on the thermal stability and crystallization behaviour of the synthesized compounds was investigated. All oligomers degrade in two major steps by first losing HCl and side chains with subsequent breakdown of the backbone. The members with short side chains, up to poly(vinyl octanoate), are amorphous and show internal plasticization, whereas those with high number of side chain carbon atoms are semi-crystalline due to side-chain crystallization. A better packing for poly(vinyl stearate) is also noticeable. The glass transition and melting temperatures as well as the onset temperature of decomposition are influenced to a larger extent by the side chain length than by the degree of polymerization. Thermal stability is improved if both the size and number of side chains increase, but only a long side chain causes a significant increase of the resistance to degradation. This results in a stabilization of PVAc so that oligomers from poly(vinyl octanoate) on are stable under atmospheric conditions. Thus, the way to design stable, chlorinated PVEs oligomers is to use a long n-alkyl side chain.}, language = {en} } @article{HarishWriggersJungketal.2016, author = {Harish, Ajay B. and Wriggers, Peter and Jungk, Juliane and Hojdis, Nils and Recker, Carla}, title = {Mesoscale Constitutive Modeling of Non-Crystallizing Filled Elastomers}, series = {Computational Mechanics}, volume = {57}, journal = {Computational Mechanics}, publisher = {Springer}, address = {Berlin}, issn = {1432-0924}, doi = {10.1007/s00466-015-1251-1}, pages = {653 -- 677}, year = {2016}, abstract = {Elastomers are exceptional materials owing to their ability to undergo large deformations before failure. However, due to their very low stiffness, they are not always suitable for industrial applications. Addition of filler particles provides reinforcing effects and thus enhances the material properties that render them more versatile for applications like tyres etc. However, deformation behavior of filled polymers is accompanied by several nonlinear effects like Mullins and Payne effect. To this day, the physical and chemical changes resulting in such nonlinear effect remain an active area of research. In this work, we develop a heterogeneous (or multiphase) constitutive model at the mesoscale explicitly considering filler particle aggregates, elastomeric matrix and their mechanical interaction through an approximate interface layer. The developed constitutive model is used to demonstrate cluster breakage, also, as one of the possible sources for Mullins effect observed in non-crystallizing filled elastomers.}, language = {en} }