Martin Kröger

Swiss Federal Institute of Technology (ETH), Materials, Faculty Member

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James Marrow

University of Oxford

Estela Blaisten-Barojas

George Mason University

Suseendran Jayachandran

IMEC

Petra Reinke

University of Virginia

Dr.Yousery Sherif

Mansoura University

Irina Kolesnik

Moscow State University

Prof.Dr. İbrahim USLU

Gazi University

Kenneth Vecchio

University of California, San Diego

Professor Dr. Loutfy H . Madkour

Al-Baha University, Kingdom of Saudi Arabia

Laura Elia Martínez Garza

Universidad Autónoma de Nuevo León

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Papers by Martin Kröger

Molekulardynamik-Computersimulation: Bestimmung dynamischer Eigenschaften aus Fluktuationen

Physik Online, 2018

Surface Disentanglement and Slip in a Polymer Melt: A Molecular Dynamics Study

Macromolecules, 2018

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Detailed atomistic molecular-dynamics simulation of the orthorhombic phase of crystalline polyethylene and alkane crystals

The Journal of Chemical Physics, 2001

Results are presented for the structural and thermodynamic properties of the orthorhombic phase o... more Results are presented for the structural and thermodynamic properties of the orthorhombic phase of crystalline polyethylene (PE) from detailed atomistic molecular-dynamics (MD) simulations in the NPT statistical ensemble. Two different PE crystal systems have been investigated: (a) paraffins consisting of an odd number of carbon atoms such as C23H48 and (b) infinite length PE monocrystals, at temperatures ranging from T=150

Crossover from the Rouse to the Entangled Polymer Melt Regime: Signals from Long, Detailed Atomistic Molecular Dynamics Simulations, Supported by Rheological Experiments

Macromolecules, 2003

Results are presented from 300 ns long atomistic molecular dynamics (MD) simulations of polyethyl... more Results are presented from 300 ns long atomistic molecular dynamics (MD) simulations of polyethylene (PE) melts, ranging in molecular length from C 78 to C250. Above C156, the self-diffusion coefficient D is seen to exhibit a clear change in its power-law dependence on the molecular weight (M), significantly deviating from a Rouse (where D ∼ M-1) toward a reptation-like (where D ∼ M-2.4) behavior. The mean-square displacement (msd) of chain segments and the dynamic structure factor is also calculated and the crossover from the Rouse to entangled behavior is again observed above C156. A novel strategy is also developed for projecting atomistic chain configurations to their primitive paths and thereby mapping simulation trajectories onto the reptation model. Results for the friction factor , the zero-shear rate viscosity η0 and the self-diffusion coefficient D are found to be internally consistent and in agreement with experimental rheological data.

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Flow of branched polymer melts in a lubricated cross-slot channel: a combined computational and experimental study

Rheologica Acta, 2008

Numerical simulations have been performed to evaluate the accuracy of the multimode Giesekus mode... more Numerical simulations have been performed to evaluate the accuracy of the multimode Giesekus model in predicting the flow behavior of a rheologically well characterized low-density polyethylene melt in a lubricated cross-slot channel. Specifically, the fidelity of the numerical results is established by detailed comparison with flow-induced birefringence measurements in a new optical rheometer with lubricated side walls that allows the creation of ideal two-dimensional flow kinematics that lead to the elimination of end effects commonly encountered in flow birefringence measurements. Based on these comparisons, the ability of the multimode Giesekus model to capture the flow characteristics with reasonable accuracy in the experimentally available Wi range of 21 to 29 has been established. However, it should be noted that the model predictions

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Dynamic structure of unentangled polymer chains in the vicinity of non-attractive nanoparticles

Soft Matter, 2014

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Primitive-path statistics of entangled polymers: mapping multi-chain simulations onto single-chain mean-field models

New Journal of Physics, 2014

We present a method to map the full equilibrium distribution of the primitivepath (PP) length, ob... more We present a method to map the full equilibrium distribution of the primitivepath (PP) length, obtained from multi-chain simulations of polymer melts, onto a single-chain mean-field 'target' model. Most previous works used the Doi-Edwards tube model as a target. However, the average number of monomers per PP segment, obtained from multi-chain PP networks, has consistently shown a discrepancy of a factor of two with respect to tube-model estimates. Part of the problem is that the tube model neglects fluctuations in the lengths of PP segments, the number of entanglements per chain and the distribution of monomers among PP segments, while all these fluctuations are observed in multi-chain simulations. Here we use a recently proposed slip-link model, which

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Insights from modeling into structure, entanglements, and dynamics in attractive polymer nanocomposites

Soft Matter, 2021

Conformations, entanglements, and dynamics in attractive polymer nanocomposites are investigated ... more

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Was ist "flüssig"?

Physik Online, 2018

Molekulardynamik-Computersimulation: Methodische Details

Physik Online, 2018

Formfaktoren für sphärische und uniaxiale Teilchen

Physik Online, 2018

Solution of the complete Curtiss-Bird model for polymeric liquids subjected to simple shear flow

The Journal of Chemical Physics, 2016

The complete kinetic theory model for concentrated polymer solutions and melts proposed by Curtis... more The complete kinetic theory model for concentrated polymer solutions and melts proposed by Curtiss and Bird is solved for shear flow: (a) analytically by providing a solution for the single-link (or configurational) distribution function as a real basis spherical harmonics expansion and then calculating the materials functions in shear flow up to second order in the dimensionless shear rate and, (b) numerically via the execution of Brownian dynamics simulations. These two methods are actually complementary to each other as the former is accurate only for small dimensionless shear rates where the latter produces results with increasingly large uncertainties. The analytical expansions of the material functions with respect to the dimensionless shear rate reduce to those of the extensively studied, simplified Curtiss-Bird model when ε ′ = 0, and to the rigid rod when ε ′ = 1. It is known that the power-law behavior at high shear rates is very different for these two extremal cases. We employ Brownian dynamics simulation to not only recover the limiting cases but to find a gradual variation of the power-law behaviors at large dimensionless shear rates upon varying ε ′. The fact that experimental data are usually located between these two extremes strongly advocates the significance of studying the solution of the Curtiss-Bird model. This is exemplified in this work by comparing the solution of this model with available rheological data for semiflexible biological systems that are clearly not captured by the original Doi-Edwards or simplified Curtiss-Bird models.

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Unraveling two-dimensional polymerization propagation from diffuse scattering

Acta Crystallographica Section A Foundations and Advances, 2016

NaLaF 4 is an efficient up-conversion phosphor [1] belonging to the family of rare earth-doped so... more NaLaF 4 is an efficient up-conversion phosphor [1] belonging to the family of rare earth-doped sodium lanthanide tetrafluorides where the nature of the photoactive sites can unambiguously be explained only in terms of a microscopic model of disorder [2]. X-ray and Neutron Diffuse Scattering (XDS, NDS), as k-space probes, provide statistically reliable data on atomic pair correlation functions and thus on deviations from the average periodic structure. Using high quality XDS and NDS datasets from the distinctive, planar diffuse scattering of NaLaF 4 , we calculated the 3D-Difference Pair Distribution Function (3D-ΔPDF), identified the various types of disorder and derived an abstract model of interatomic vectors [3]. It was then possible by means of Monte Carlo (MC) simulations to build and optimize large model crystals providing a specific atomistic disorder model for NaLaF 4 , whose Fourier transform gives an excellent fit to the experimental diffuse scattering. The distinct contrast displayed by the various atomic species with the two radiation types provides a better sensitivity to the different pair-wise correlations ultimately yielding more robust results.

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Self-assembled core-polyethylene glycol-lipid shell nanoparticles demonstrate high stability in shear flow

Physical chemistry chemical physics : PCCP, Jan 11, 2017

A core-polyethylene glycol-lipid shell (CPLS) nanoparticle consists of an inorganic core coated w... more A core-polyethylene glycol-lipid shell (CPLS) nanoparticle consists of an inorganic core coated with polyethylene glycol (PEG) polymers, surrounded by a lipid bilayer shell. It can be self-assembled from a PEGylated core with surface-tethered PEG chains, where all the distal ends are covalently bonded to lipid molecules. Upon adding free lipids, a complete lipid bilayer shell can be formed on the surface driven by the hydrophobic nature of lipid tails, leading to the formation of a CPLS nanoparticle. The stability of CPLS nanoparticles in shear flow has been systematically studied through large scale dissipative particle dynamics simulations. CPLS nanoparticles demonstrate higher stability and less deformation in shear flow, compared with lipid vesicles. Burst leakage of drug molecules inside lipid vesicles and CPLS NPs can be induced by the large pores at their tips. These pores are initiated by the maximum stress in the waist region. It further grows along with the tank-treading m...

Dynamics of Branched Polymer Melts in Complex Kinematics Flows: A Computational∕Experimental Study

AIP Conference Proceedings, 2008

... well in predicting the steady flow kinematics and stress field of moderately concentrated pol... more

Mesosocopic model for the viscosities of nematic liquid crystals

Topological and Dynamical Mapping of Atomistic Simulation Data Onto the Tube Model for Entangled Polymer Melts

Canonical distribution functions in polymer dynamics. (I). Dilute solutions of flexible polymers

Physica A: Statistical Mechanics and its Applications, 2002

The quasi-equilibrium or maximum entropy approximation is applied in order to derive constitutive... more The quasi-equilibrium or maximum entropy approximation is applied in order to derive constitutive equations from kinetic models of polymer dynamics. It is shown in general and illustrated for an example how canonical distribution functions are obtained from the maximum entropy principle, how macroscopic and constitutive equations are derived therefrom and how these constitutive equations can be implemented numerically. In addition, a measure for the accuracy of the quasi-equilibrium approximation is proposed that can be evaluated while integrating the constitutive equations. In the example considered, it is confirmed that the accuracy of the approximation is increased by including more macroscopic variables. In steady elongational flow, it is found that more macroscopic variables need to be included above the coil-stretch transition to achieve the same accuracy as below.

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Collapse of Thermoresponsive Brushes and the Tuning of Protein Adsorption

Macromolecules, 2011

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Ternary Protein Adsorption onto Brushes: Strong versus Weak

Langmuir, 2009

Attractive interactions between proteins and polyethylene glycol (PEG) give rise to ternary adsor... more Attractive interactions between proteins and polyethylene glycol (PEG) give rise to ternary adsorption within PEG brushes. Experimental evidence suggests two ternary adsorption modes: (i) weak, due to nonspecific weak attraction between PEG monomers and the surface of the protein, as exemplified by serum albumin and (ii) strong, due to strong binding of PEG segments to specific protein sites as it occurs for PEG antibodies, which can involve the terminal adsorption of free chain ends or backbone adsorption due to binding to interior chain segments. Ternary adsorption affects the capacity of brushes to repress protein adsorption. The strong adsorption of antibodies can trigger an immune response that may affect the biocompatibility of the surface. Theoretical adsorption isotherms and protein concentration profiles of the three cases are compared for "parabolic" brushes, allowing for the grafting density, 1 / Σ , and degree of polymerization of the PEG chains, N, as well as the volume and surface area of the proteins. The amount of adsorbed protein per unit area, Γ, exhibits a mode-specific maximum in all three cases. For backbone and weak adsorption, Γ ∼ N, whereas for terminal adsorption, Γ ∼ N 0. In every case, the concentration profile of adsorbed proteins, c tern (z), exhibits a maximum at z max >0 that shifts outward as Σ decreases; z max =0 occurs only for weak and backbone adsorption at a high Σ value.

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Molekulardynamik-Computersimulation: Bestimmung dynamischer Eigenschaften aus Fluktuationen

Physik Online, 2018

Surface Disentanglement and Slip in a Polymer Melt: A Molecular Dynamics Study

Macromolecules, 2018

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Detailed atomistic molecular-dynamics simulation of the orthorhombic phase of crystalline polyethylene and alkane crystals

The Journal of Chemical Physics, 2001