conferences

Here you find a list of my conference contribution. The name of the respective presenting author is underlined.

2014

6th European Conference on Computational Fluid Dynamics (ECFD VI), Barcelona, July 2014
“The response of semi-flexible dense polymer brushes to shear flow.”, talk [1]
F. Römer, D. A. Fedosov, doi:10.13140/2.1.3167.1045
abstract

9th Annual European Rheology Conference (AERC), Karlsruhe, April 2014
“Dense semiflexible polymer brushes in flow a model for glycocalyx layer in blood vessels”, talk
F. Römer, D. A. Fedosov

DPG Spring Meeting, Dresden, April 2014
“Semi-Flexible dense polymer brushes in flow – simulation & theory”, talk [1]
F. Römer, D. A. Fedosov

2012

10th International Meeting on Thermodiffusion (IMT10), Brussels, June 2012
“Aqueous solutions of alkali halide salts under a thermal gradient: A non equilibrium molecular dynamic study.”, talk
F. Römer, F. Bresme, doi:10.13140/2.1.4341.7602
abstract

2011

Thermodynamics, Athens, August-September 2011
“Molecular alignment under thermal gradients: A non-equilibrium molecular dynamics study”, talk
F. Römer, F. Bresme, doi:10.13140/2.1.2995.9364
abstract

85th ACS Colloid and Surface Science Symposium, Montreal, June 2011
“Formation of zinc nano particles in a carrier gas investigated by molecular dynamics simulation”, poster
F. Römer, T. Kraska

DPG-Frühjahrstagung, Molecular Physics Devision, Dresden, March 2011
“Molecular fluids under thermal gradient”, talk
F. Römer, F. Bresme, doi:10.13140/2.1.3716.8327

2010

Bunsentagung, Bielefeld, May 2010
“MD Simulation der Herstellung pharmazeutischer Partikel durch schnelle Expansion einer überkritischen Lösung”, poster
F. Römer, T. Kraska

12th European Meeting on Supercritical Fluids, Session: Health Science, Graz, May 2010
“Supercritical fluids as novel particle formation media: 2-molecular dynamics simulation of particle formation.”, talk
F. Römer, T. Kraska

DPG-Frühjahrstagung, Regensburg, März 2010
“Naproxen particle by RESS: A molecular dynamic study.”, talk
F. Römer, T. Kraska

EFCE, Processnet, Molecular Modelling and Simulation for Industrial Applications: Physico-Chemical Properties and Processes, Session: Nanoscale Processes, Würzburg, March 2010
“Molecular dynamics simulation of particle formation by rapid expansion of a supercritical solution (RESS)”, talk
F. Römer, T. Kraska

Processnet, FA Fluidverfahrenstechnik und Hochdruckverfahrenstechnik, Fulda, March 2010
“Molekulardynamische Simulation des RESS Prozesses”, talk
F. Römer, T. Kraska

2009

18th International Conference on Nucleation & Atmospheric Aerosols ICNAA, Prague, August 2009
“Formation of pharmaceutical particles by rapid expansion of a supercritical solution investigated by MD simulation”, poster
F. Römer, T. Kraska
abstract

Bunsentagung 2009, Köln, May 2009
“Molecular dynamics simulation of the formation of pharmaceutical particles by rapid expansion of a supercritical solution”, talk
F. Römer, T. Kraska
“Interface properties and phase stability of pure bulk phases”, poster (more…)
T. Kraska, F. Römer, A. Imre
“Influence of the carrier gas on the Zn particle formation from the vapour phase”, poster
S. Braun, F. Römer, T. Kraska

DPG-Frühjahrstagung, Dresden, März 2009
“Molecular dynamics simulation of the formation of pharmaceutical particles by rapid expansion of a supercritical solution”, talk
F. Römer, T. Kraska

ProcesNet Jahrestreffen des FA Hochdruckverfahrenstechnik und des TAK Phytoextrakte, Fraunhofer-Institut UMSICHT, Oberhausen, März 2009
“Experimentelle und theoretische Untersuchungen zur Herstellung von submikronen Wirkstoffpartikeln mit dem RESS-Verfahren”, tandem talk
M. Türk, D. Bolten, F. Römer, T. Kraska

2008

NATO Advanced Research Workshop Metastable Systemst Under Pressure: Platform for New Technologies and Environmental Applications, Odessa, October 2008
“Estimation of explosive boiling limit of metastable liquids”, talk
A. R. Imre, G. Mayer, G. Házi, R. Rozas, F. Römer and T. Kraska

Thermodynamik-Kolloquium, ProcessNet, VDI/Dechema, Erlangen, September 2008
“Vorhersage thermodynamischer Stabilitätsgrenzen aus molekularen Simulationen”, talk
F. Römer, R. Rozas, A. R. Imre, T. Kraska

CCP5 annual meeting: Surfeaces and interfaces, London, September 2008
“The relation of interfacial properties and phase stability”, talk
F. Römer, A. R. Imre, T. Kraska

EMLG/JMLG 2008 Annual Meeting, Understanding Solvationfrom Liquid to Supercritical Conditions, Lisboa, Aug.-Sep. 2008
“A novel method to determine bulk stability limits for pure liquids from interfacial properties”, talk
A. R. Imre, G. Mayer, G. Házi, R. Rozas, F. Römer and T. Kraska

Faraday Discussion 141: Water – From Interfaces to the Bulk, Edinburgh, August 2008
“Estimation of the liquid-vapour spinodal for water and other liquids from interfacial properties”, poster
A. R. Imre, G. Mayer, G. Házi, R. Rozas, F. Römer and T. Kraska

23rd European Symposium on Applied Thermodynamics, Cannes, May/June 2008
“Determination of the spinodals of pure fluids from interfacial properties: molecular dynamics and Lattice Boltzmann simulations”, talk
A. R. Imre, G. Mayer, G Házi, F. Römer, R. Rozas, T. Kraska
“Formation of zinc nanoparticles in a carrier gas investigated by MD: homogenous nucleation and structure formation”, poster
F. Römer, T. Kraska

Bunsentagung, Saarbrüken, Mai 2008
“Molekulardynamische Untersuchung der Bildung und der Eigenschaften von Zink-Nanopartikeln”, poster
F. Römer, T. Kraska

“MD Untersuchung der Ausbildung unterschiedlicher hcp-Oberflächen bei Zink-Nanopartikeln”, poster
S. Braun, F. Römer, T. Kraska

9. Kinetikseminar der DGKK, Aachen, March 2008
“MD Untersuchung der Ausbildung unterschiedlicher hcp-Oberflächen bei der Bildung von Zinkclustern in der Gasphas”, poster
S. Braun, F. Römer, T. Kraska

DPG-Frühjahrstagung, Berlin, Februar 2008
“Homogeneous nucleation and growth in supersaturated zinc vapour”, talk
F. Römer, T. Kraska

“Zinc nano-cluster investigated by Molecular Dynamic Simulations”, poster
S. Braun, F. Römer, T. Kraska

2007

DPG-Frühjahrstagung, Regensburg, März 2007
“Development of an EAM potential for hcp metals (Ru,Zn)”, poster
F. Römer, T. Kraska


[1] The theoretical part of these slides is outdated! Here you can find an updated version.

The response of dense brushes of semi-flexible polymers to flow is of great interest in both technological and biological contexts. Examples include the glycocalyx or the endothelial surface layer in blood vessels and mucus-like layers in lungs.
We employ smoothed dissipative particle dynamics (SDPD) method, a mesoscopic hydrodynamics technique, to study semi-flexiblepolymer brushes for a wide range of conditions including grafting density, polymer elasticity, and shear stress due to flow Our simulation results are in good agreement with previous studies, which focused on brushes with low grafting densities. We also propose a theoretical model which describes the deformation of dense semi-flexiblepolymer brushes in shear flow for a wide parameter range. The model allows us to predict effective deformation (height), monomer density profile and hydrodynamic penetration depth (solvent velocity profile) within a brush. Finally, we also investigate the interactions between a modeled glycocalyx and flowng blood cells.
The response of dense brushes of semi-flexible polymers to flow is of great interest in both technological and biological contexts. Examples include the glycocalyx on the endothelial surface layer in blood vessels [S. Weinbaum et al., Annu. Rev. Biomed. Eng. 9, 121–167, 2007] and mucus-like layers in lungs or the interior of nuclear pores.
We employ smoothed dissipative particle dynamics (SDPD) [P. Espanol, M. Revenga, Phys. Rev. E 67, 026705, 2003] simulations to study semi-flxible polymer brushes for a wide range of conditions including grafting density, polymer elasticity, and shear stress due to flow. Our simulation results are in good agreement with previous studies [Y.W. Kim et al., Macromolecules 42, 3650–3655, 2009], which focused on brushes with low grafting densities. We also propose a theoretical model which describes the deformation of dense semi-flexible polymer brushes in shear flow for a wide parameter range. The model allows us to predict effective deformation (height), inner density profile and hydrodynamic penetration depth (solvent velocity profile). Therefore, it is suitable to predict the effect of grafted surfaces on the flow profile in a slit or tube.
Non equilibrium phenomena play an important role in many processes of relevance in chemistry, biology, physics as well as in material science. Chemical reactions in small compartments (e.g. lab-on-a-chip devices) can result in large thermal gradients. We have performed non-equilibrium molecular dynamics (NEMD) simulations to study the different contributions to the heat conduction and the influence of the thermal gradient on the non equilibrium response of molecular fluids. We show that anisotropic molecules adopt a preferred orientation with respect to the thermal gradient. We illustrate this notion with diatomic molecules modelled using two Lennard Jones (LJ) sites, so called two centre LJ models (2CLJ), connected by a flexible bond. Using this model we investigate the mechanism of heat transport and the molecular alignment with the temperature gradient as a function of the molecule interaction parameters.
With a recently developed method (J. Phys. Chem. C 113, 19028-19038, 2009) we study the formation of Naproxen particles by expansion of a supercritical solution (RESS) by means of molecular dynamics simulation. For this investigation we propose a new potential model for Naproxen. The employed van der Waals parameters are based on the TraPPE model. The charges and intramolecular interactions due to internal degrees of freedom are obtained from ab initio calculations. We analyze the bulk properties of the Naproxen model as well as those of small particles. The expansion path of a Naproxen/CO2 solution is compared to the napthalene/CO2 system. For a wide range of pre-expansion conditions (310 K – 400 K) we determine the nucleation rates and compare them to calculations with the the classical nucleation theory.
Rapid Expansion from Supercritical Solution (RESS) is a method for the production of small particles down to the nanometre size for various substances including pharmaceuticals. The substance is dissolved in a supercritical solvent, typically carbon dioxide, and then expanded in a nozzle. This leads to lowering of the solubility and hence to a very high supersaturation. As a consequence the solute precipitates from the solution. We investigate this process by molecular dynamics simulation. An equilibrated supercritical solution is expanded by successive expansion of the simulation box. The parameters of the expansion are chosen to closely follow the path of an adiabatic expansion while preventing the phase separation of the solvent. The particles obtained in this way are investigated with respect to their structure and properties.
We perform molecular dynamics simulation with a new parameterisation of the embedded atom method [1] in order to investigate the formation of zinc nano-cluster. First we focus on the homogeneous nucleation in supersaturated zinc vapour simulation [2]. Argon is added to the vapour phase, which acts as inert gas thermostat to remove the latent heat from the forming clusters. We compare two methods for the detection of clusters namely the Stillinger criterion based on atom distances only and the ten Wolde-Frenkel cluster definition requiring at least five next neighbours for each atom to be part of a cluster. To obtain the nucleation rates and the critical cluster sizes, we use the so-called threshold method by Yasuoka and Matsumoto [3] and a mean first passage time method by Wedekind et al. [4]. The simulation results show large deviation to the classical nucleation theory. A similar deviation has been found for experimental data in comparison to the classical nucleation theory. Nano-clusters exhibit differences in several properties compared to the bulk phase. In this context zinc is especially interesting because it is a hcp metal with a large deviation of the lattice axis ratio c/a to the ideal value corresponding to close packing. We study the structure and morphology of the clusters for different temperatures and cluster sizes [1]. Besides using the radial distribution function we employ the common neighbour analysis (CNA), which allows to determine details of the structural composition of the clusters. For this investigation we have developed CNA signatures especially for hcp-surfaces that are important for particle growth. Depending on the cluster size different types of surfaces appear and can also vanish again. We furthermore analyse the thermal expansion and the equilibrium distance of the lattice constants for solid-like clusters. [1] F. Römer, S. Braun, T. Kraska, Phys. Chem. Chem. Phys. submitted [2] F. Römer, T. Kraska, J. Chem. Phys. 127, (2007) [3] K. Yasuoka, M. Matsumoto, J. Chem. Phys. 109, 8451 (1998) [4] J. Wedekind et al., J. Chem. Phys. 126, 134103 (2007)
Zink Nanopartikel sind von Interesse sowohl bei technischen Prozessen wie der solarthermischen Gewinnung von Wasserstoff als auch hinsichtlich grundlegender Fragestellungen wie die Strukturbildung in hcp Metallen, die eine starke Abweichung von dem idealen Verhältnis der Gitterkonstanten haben. Wir haben uns mit der Bildung von Zink Nanopartikeln aus der Gasphase mittels molekulardynamischer Simulationen beschäftigt. Einerseits haben wir die Keimbildungsraten mit verschiedenen numerischen Analysemethoden untersucht, andererseits haben wir die Ausbildung der Struktur der Cluster untersucht. Hierbei wurde besonderes Augenmerk auf die Bildung und Umwandlung unterschiedlicher hcp-Oberflächen gelegt. Mit dem EAM-Potentialmodell für Zink, das wir für diese Untersuchung entwickelt haben, werden Struktur und Eigenschaften in der Bulkphase ebenso wiedergegeben wie der Dimerabstand in der Gasphase. Ferner ist das Modell in der Lage die Strukturen sowie die Gitterkonstanten und deren anisotrope thermische Ausdehnung wiederzugeben.
Zink Nanopartikel sind von Interesse sowohl bei technischen Prozessen wie der solarthermischen Gewinnung von Wasserstoff als auch hinsichtlich grundlegender Fragestellungen wie die Strukturbildung in hcp Metallen, die eine starke Abweichung von dem idealen Verhältnis der Gitterkonstanten haben. Wir haben uns mit der Bildung von Zink Nanopartikeln aus der Gasphase mittels molekulardynamischer Simulationen beschäftigt. Mit dem EAM-Potentialmodell für Zink, das wir für diese Untersuchung entwickelt haben, werden Struktur und Eigenschaften in der Bulkphase ebenso wiedergegeben wie der Dimerabstand in der Gasphase. Ferner ist es in der Lage die Strukturen sowie die Gitterkonstanten und deren anisotrope thermische Ausdehnung wiederzugeben. Wir berichten hier über die Ausbildung der Struktur von Zink Clustern. Es wurde besonderes Augenmerk auf die Bildung und Umwandlung unterschiedlicher hcp-Oberflächen gelegt. Für kleine Cluster finden wir zunächst bei 300 bis 400 K hcp und fcc Struktur, die sich beim Abkühlen auf 50 K zu einem großen Teil in icosaedrische Struktur umwandelt. Dies ist sowohl der Fall für die Oberflächenatome als auch für die Atome im Inneren des Clusters. Bei großen Clustern beobachtet man hingegen, das bei 300 bis 400 K noch eine signifikante Menge icosaedrischer Struktur vorhanden ist, die beim Abkühlen auf 50 K vollständig verloren geht. Statt dessen bilden sich hcp-Oberflächen aus, deren Häufigkeit ihrer Abfolge in der Stabilität entspricht.
We investigate the homogeneous nucleation of supersaturated zinc vapour by non-equilibrium molecular dynamics simulation [1]. Argon is added to the vapour phase, which acts as inert gas thermostat to remove the latent head from the forming clusters. Our simulations cover a temperature range from 400 K to 800 K and a supersaturation ranging from log(S) = 2 to 11. We compare two methods for the detection of clusters namely the Stillinger criterion based on atom distances only and the ten Wolde-Frenkel cluster definition requiring at least five next neighbours for each atom to be part of a cluster. To obtain the nucleation rates and the critical cluster sizes, we use the so-called threshold method by Yasuoka and Matsumoto [2] and a mean first passage time method by Wedekind et al. [3]. The simulation results show large deviation to the classical nucleation theory. A similar deviation has been found for experimental data in comparison with the classical nucleation theory. In conclusion the experimental data and simulations are in different domains with respect to supersaturation but both deviate consistently from the classical nucleation theory. [1] F. Römer, T. Kraska, J. Chem. Phys. in press [2] K. Yasuoka, M. Matsumoto, J. Chem. Phys. 109, 8451 (1998) [3] J. Wedekind et al., J. Chem. Phys. 126, 134103 (2007)
We perform molecular dynamics simulation with a recently developed new parameterisation of the embedded atom method (EAM) in order to investigate zinc nano-cluster. Nano-clusters exhibit differences in several properties compared to the bulk phase. In this context zinc is especially interesting because it is a hcp metal with a large deviation of the lattice axis ratio c/a to the ideal value corresponding to close packing. The clusters investigated here are obtained in prior particle formation simulations in a supersaturated vapour. The clusters are naturally grown including cluster-cluster collisions and sintering. Influences of the initial configuration to the resulting structures are not present. To control the temperature of the clusters we add argon as carrier gas which itself is coupled to a MD thermostat. We study the structure and morphology of the clusters for different temperatures and cluster sizes. Besides using the radial distribution function we employ the common neighbour analysis (CNA), which allows to determine details of the structural composition of the clusters. For this investigation we have developed CNA signatures especially for hcp-surfaces that are important for particle growth. We also analyse the thermal expansion and the equilibrium distance of the lattice constants for solid-like clusters.