I've just started setting up a research group on 'Multiscale Materials Modeling' (M3)
at the Institute for Computational Physics (ICP),
University of Stuttgart.
In general, my research is largely curiosity driven and concerns the interface
between chemical physics, physical chemistry, statistical physics but also questions from biology and
material science. I use computer simulations and statistical mechanics as principal tool,
but I also stay in close touch with experiments.
I will iregularly post some insights I feel worth sharing in my blog.
Feel free to check my CV
(last updated 2020/08/04) or to contact me!
We have just published
MAICoS - Molecular Analysis for Interfacial and Confined Systems.
MAICos is a Python library to analyse molecular dynamics simulations of
interfacial and confined systems based on MDAnalysis.
For now the most important features cover the analysis of
dielectric profiles in different geometries and various tools
to invertigate the interfacial structure and velocity profiles.
Check it out for here and provide us feedback using the bugtracker if you have any suggestions or problems!
From water cavitation to hydration repulsion
Liquids at interfaces show many properties different from their bulk due to the
different forces that are experienced.
The force balance between the different phases is typically described in terms
of the wetting coefficient
The free energy difference between a confined liquid and in bulk then
determines if the cavity is filled at given values of temperature and pressure,
and, more importantly, if the surface interaction is attractive or repulsive.
Using molecular simulations of water at controlled chemical potential between
surfaces with tunable , we were able to obtain the interaction
phase diagram .
The precise knowledge and understanding of the water-mediated interactions is
not only of crucial importance for industrial applications, but also in biology
where the hydration repulsion ultimately stabilizes biological membranes at
nanometer separations .
Although known since many years, its physical origin is still under debate.
In my work I use simulations of atomistically represented water between
membranes to obtain further insights into possible mechanisms for this
M. Kanduč, A. Schlaich, E. Schneck, and R. R. Netz, “Water-Mediated Interactions between Hydrophilic and Hydrophobic Surfaces,” Langmuir, vol. 32, no. 35, pp. 8767–8782, Sep. 2016. [WEB][DOI]
A. Schlaich, B. Kowalik, M. Kanduč, E. Schneck, and R. R. Netz, “Physical mechanisms of the interaction between lipid membranes in the aqueous environment,” Physica A, vol. 418, pp. 105–125, Jan. 2015. [WEB][DOI]
Electrostatic and dielectric effects at interfaces and in confinement
Many biologically and industrially relevant surfaces are charged in water,
classical examples are lipid membranes, ionic surfactant layers and solid
surfaces such as glass, silica or mica. The resulting interactions are
profoundly influenced by water polarization, which in a macroscopic approach is
quantified by means of the static dielectric tensor. Whereas the latter is
constant and diagonal in bulk, close to an interface, the effect of the water
structure is more intricate .
Using atomistic molecular dynamics simulations, we calculate the space-dependent dielectric
response function of water in confinement and find that the effective
dielectric permitivitty is strongly influenced for a confined planar water slab
Finally, by performing simulations of charged surfaces at controlled water
chemical potential both the ion distribution and the interaction pressure
are accessible .
Importantly, already for moderate surface charge densities the additivity of
the hydration pressure and mean-field electrostatic repulsion breaks down,
due to a combination of different effects, namely, counterion
correlations as well as the surface charge-induced reorientation of hydration
water, which modifies the effective water dielectric constant as well as the
P. Loche, C. Ayaz, A. Schlaich, D. J. Bonthuis, and R. R. Netz, “Breakdown of Linear Dielectric Theory for the Interaction between Hydrated Ions and Graphene,” J. Phys. Chem. Lett., vol. 9, no. 22, pp. 6463–6468, Nov. 2018. [WEB][DOI]
A. Schlaich, E. W. Knapp, and R. R. Netz, “Water Dielectric Effects in Planar Confinement,” Phys. Rev. Lett., vol. 117, no. 4, p. 048001, Jul. 2016. [WEB][DOI]
A. Schlaich, A. P. dos Santos, and R. R. Netz, “Simulations of Nanoseparated Charged Surfaces Reveal Charge-Induced Water Reorientation and Nonadditivity of Hydration and Mean-Field Electrostatic Repulsion,” Langmuir, vol. 35, no. 2, pp. 551–560, Jan. 2019. [WEB][DOI]
Adsorption and transport in hierarchical porous materials
Porous materials combining several porosity scales, such as hierarchical zeolites,
are widely used in industry for adsorption, separation or catalysis
to overcome slow diffusion in strongest confinement (< 2 nm)
and enhance access to the materials large surface area.
Available modeling approaches for adsorption and transport in such multiscale
porous media are limited to empirical parameters which cannot be derived
from molecular coefficients.
In particular, existing approaches do not offer the ground for a bottom up
model of adsorption/transport in multiscale materials as
(1) they describe empirically the adsorption/transport interplay and
(2) they do not account for the molecular details of hydrodynamics at the nm scale.
We use atom-scale molecular simulations to obtain explicit relations between
adsorption and the transport coefficients, which capture different regimes upon
varying the temperature, pore size, pressure, etc.
This research is conducted within the ANR project
that aims at developing a bottom up model of adsorption/transport in multiscale
porous materials using experiment, molecular simulation and theory.
We employ a rigorous statistical mechanics upscaling strategy to connect
parameters from molecular to engineering scales without losing information at
the lower scale. Owing to the use of data that capture the many
adsorption/transport regimes upon varying pressure, pore size, etc., this
approach does not rely on hydrodynamics and, hence, does not require assuming a
given adsorption/flow type.
Alexander Schlaich Office 1.036 Institute for Computational Physics Universität Stuttgart Allmandring 3 70569 Stuttgart Germany Phone +49 711 685-63607 Fax +49 711 685-63658