Nanoscale Fluid Transport

We study the interaction of fullerenes with water and biomolecules, aiming to contribute in the design of nanosensors for bio-nanotechnology applications and nanoscale devices for water purification and desalination.

Fullerenes in Liquids

Fullerenes are a family of carbon allotropes, molecules composed entirely of carbon, which form hollow spheres, ellipsoids, tubes, or planes. Their unique physical properties make them excellent candidates for applications ranging from gas sensors to targeted drug design and delivery. We focus on the interaction of fullerenes with fluids as we are interested in the design of nanosensors and actuators.

We investigate the transport of water and ion solutions in nanoscale systems, such as carbon nanotubes (CNTs). For our analysis we employ continuum approaches and particle Methods (Molecular Dynamics Simulations). We investigate how interaction and simulation parameters can affect the uncertainty of calculated observables. With Uncertainty Quantification studies we calibrate simulation parameters to better fit distribution of experimental observables.

In numerous experiments calculated flow rates of water confined in Carbon Nanotubes exceed the expected theoretical estimations. The origin of such enhanced nanofluidic transport is being investigated. Candidate effects such as CNT vibrations and structural and chemical abnormalities of the CNT surface are put into the test to decipher such phenomena in the nanoscale.

Water and CNT animation
Hydrophobic interaction of water and CNT
Water flow in Double-Walled CNT
Detail at CNT wall

Electrophoretic RNA transport through transmembrane carbon nanotubes

We use molecular  dynamics simulations to study the electrophoretic transport of RNA through carbon nanotubes embedded in membranes. Decorated and naked carbon nanotubes are inserted into a dodecane membrane and a dimyristoylphosphatidylcholine lipid bilayer, and the system is subjected to electrostatic potential differences. The transport properties of this artificial pore are determined by the structural modifications of the membrane in the vicinity of the nanotube openings and they are quantified by the nonuniform electrostatic potential maps at the entrance and inside the nanotube.

Carbon nanotubes as toxic gas  sensors

Recent experimental results have shown that carbon nanotube based sensors are promising transductors elements for gas sensors. The carbon nanotubes show both a high sensitivity to low  concentrations of nitrogen dioxide (NO2) as well as  low power consumption. In cooperation with the Micro and Nanosystems group we seek to better understand the mechanism with which Single Walled Carbon Nanotubes (SWCNT) react to the presence of nitrogen dioxide in a gas.

People: Evangelos Kotsalis, Jens Honoré Walther, Alvaro Foletti
Collaborators: Professor C. Hieriold, Dr. R. Cosmin(ETHZ), Dr. Richard Jaffe (NASA Ames)

Computational Approach and Challenges

Using molecular dynamics (MD) we simulate systems comprising of solutes and carbon-based structures, such as Carbon Nanotubes (CNTs). High Performance Computing is employed in order to reach sufficient length and time-scales for our systems. Different multiscale approaches based on the experitise of the CSE lab  are being explored to bridge the gap of scales between nanoscale simulation results and larger scale experimental data.

Publications

2015

  • P. R. Jones, X. Hao, E. R. Cruz-Chu, K. Rykaczewski, K. Nandy, T. M. Schutzius, K. K. Varanasi, C. M. Megaridis, J. H. Walther, P. Koumoutsakos, H. D. Espinosa, and N. A. Patankar, “Sustaining dry surfaces under water," Sci. Rep.-UK, vol. 5, iss. 1, 2015.
    [BibTeX] [Abstract] [PDF] [DOI]

    Rough surfaces immersed under water remain practically dry if the liquid-solid contact is on roughness peaks, while the roughness valleys are filled with gas. Mechanisms that prevent water from invading the valleys are well studied. However, to remain practically dry under water, additional mechanisms need consideration. This is because trapped gas (e.g. air) in the roughness valleys can dissolve into the water pool, leading to invasion. Additionally, water vapor can also occupy the roughness valleys of immersed surfaces. If water vapor condenses, that too leads to invasion. These effects have not been investigated, and are critically important to maintain surfaces dry under water. In this work, we identify the critical roughness scale, below which it is possible to sustain the vapor phase of water and/or trapped gases in roughness valleys {–} thus keeping the immersed surface dry. Theoretical predictions are consistent with molecular dynamics simulations and experiments.

    @article{jones2015a,
author = {Paul R. Jones and Xiuqing Hao and Eduardo R. Cruz-Chu and Konrad Rykaczewski and Krishanu Nandy and Thomas M. Schutzius and Kripa K. Varanasi and Constantine M. Megaridis and Jens H. Walther and Petros Koumoutsakos and Horacio D. Espinosa and Neelesh A. Patankar},
doi = {10.1038/srep12311},
journal = {{Sci. Rep.-UK}},
month = {aug},
number = {1},
publisher = {Springer Nature},
title = {Sustaining dry surfaces under water},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/jones2015a.pdf},
volume = {5},
year = {2015}
}

2013

  • J. H. Walther, K. Ritos, E. R. Cruz-Chu, C. M. Megaridis, and P. Koumoutsakos, “Barriers to superfast water transport in carbon nanotube membranes," Nano Lett., vol. 13, iss. 5, p. 1910–1914, 2013.
    [BibTeX] [Abstract] [PDF] [DOI]

    Carbon nanotube (CNT) membranes hold the promise of extraordinary fast water transport for applications such as energy efficient filtration and molecular level drug delivery. However, experiments and computations have reported flow rate enhancements over continuum hydrodynamics that contradict each other by orders of magnitude. We perform large scale molecular dynamics simulations emulating for the first time the micrometer thick CNTs membranes used in experiments. We find transport enhancement rates that are length dependent due to entrance and exit losses but asymptote to 2 orders of magnitude over the continuum predictions. These rates are far below those reported experimentally. The results suggest that the reported superfast water transport rates cannot be attributed to interactions of water with pristine CNTs alone.

    @article{walther2013a,
author = {Jens H. Walther and Konstantinos Ritos and Eduardo R. Cruz-Chu and Constantine M. Megaridis and Petros Koumoutsakos},
doi = {10.1021/nl304000k},
journal = {{Nano Lett.}},
month = {may},
number = {5},
pages = {1910--1914},
publisher = {American Chemical Society ({ACS})},
title = {Barriers to Superfast Water Transport in Carbon Nanotube Membranes},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/walther2013a.pdf},
volume = {13},
year = {2013}
}

2008

  • U. Zimmerli and P. Koumoutsakos, “Simulations of electrophoretic RNA transport through transmembrane carbon nanotubes," Biophys. J., vol. 94, iss. 7, p. 2546–2557, 2008.
    [BibTeX] [Abstract] [PDF] [DOI]

    The study of interactions between carbon nanotubes and cellular components, such as membranes and biomolecules, is fundamental for the rational design of nanodevices interfacing with biological systems. In this work, we use molecular dynamics simulations to study the electrophoretic transport of RNA through carbon nanotubes, embedded in membranes. Decorated and naked carbon nanotubes are inserted into a dodecane membrane and a dimyristoylphosphatidylcholine lipid bilayer, and the system is subjected to electrostatic potential differences. The transport properties of this artificial pore are determined by the structural modifications of the membrane in the vicinity of the nanotube openings and they are quantified by the nonuniform electrostatic potential maps at the entrance and inside the nanotube. The pore is used to transport electrophoretically a short RNA segment and we find that the speed of translocation exhibits an exponential dependence on the applied potential differences. The RNA is transported while undergoing a repeated stacking and unstacking process, affected by steric interactions with the membrane headgroups and by hydrophobic interaction with the walls of the nanotube. The RNA is structurally reorganized inside the nanotube, with its backbone solvated by water molecules near the axis of the tube and its bases aligned with the nanotube walls. Upon exiting the pore, the RNA interacts with the membrane headgroups and remains attached to the dodecane membrane while it is expelled into the solvent in the case of the lipid bilayer. The results of the simulations detail processes of molecular transport into cellular compartments through manufactured nanopores and they are discussed in the context of applications in biotechnology and nanomedicine.

    @article{zimmerli2008a,
author = {Urs Zimmerli and Petros Koumoutsakos},
doi = {10.1529/biophysj.106.102467},
journal = {{Biophys. J.}},
month = {apr},
number = {7},
pages = {2546--2557},
publisher = {Elsevier {BV}},
title = {Simulations of Electrophoretic {RNA} Transport Through Transmembrane Carbon Nanotubes},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/zimmerli2008a.pdf},
volume = {94},
year = {2008}
}

2005

  • E. M. Kotsalis, E. Demosthenous, J. H. Walther, S. C. Kassinos, and P. Koumoutsakos, “Wetting of doped carbon nanotubes by water droplets," Chem. Phys. Lett., vol. 412, iss. 4-6, p. 250–254, 2005.
    [BibTeX] [Abstract] [PDF] [DOI]

    We study the wetting of doped single- and multi-walled carbon nanotubes by water droplets using molecular dynamics simulations. Chemisorbed hydrogen is considered as a model of surface impurities. We study systems with varying densities of surface impurities and we observe increased wetting, as compared to the pristine nanotube case, attributed to the surface dipole moment that changes the orientation of the interfacial water. We demonstrate that the nature of the impurity is important as here hydrogen induces the formation of an extended hydrogen bond network between the water molecules and the doping sites leading to enhanced wetting.

    @article{kotsalis2005a,
author = {E.M. Kotsalis and E. Demosthenous and J.H. Walther and S.C. Kassinos and P. Koumoutsakos},
doi = {10.1016/j.cplett.2005.06.122},
journal = {{Chem. Phys. Lett.}},
month = {sep},
number = {4-6},
pages = {250--254},
publisher = {Elsevier {BV}},
title = {Wetting of doped carbon nanotubes by water droplets},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/kotsalis2005a.pdf},
volume = {412},
year = {2005}
}

2004

  • E. M. Kotsalis, J. H. Walther, and P. Koumoutsakos, “Multiphase water flow inside carbon nanotubes," Int. J. Multiphas. Flow, vol. 30, iss. 7-8, p. 995–1010, 2004.
    [BibTeX] [Abstract] [PDF] [DOI]

    We present nonequilibrium molecular dynamics simulations of the flow of liquid-vapour water mixtures and mixtures of water and nitrogen inside carbon nanotubes. A new adaptive forcing scheme is proposed to impose a mean flow through the system. The flow of liquid water is characterised by a distinct layering of the water molecules in the vicinity of the boundary and a slip length that is found to increase with the radius of the carbon nanotube. Increasing the temperature and pressure of the system furthermore results in a decrease in the slip length. For the flow of mixtures of nitrogen and water we find that the slip length is reduced as compared to the slip for the pure water. The shorter slip length is attributed to the fact that nitrogen forms droplets at the carbon surface, thus partially shielding the bulk flow from the hydrophobic carbon surface.

    @article{kotsalis2004a,
author = {E.M. Kotsalis and J.H. Walther and P. Koumoutsakos},
doi = {10.1016/j.ijmultiphaseflow.2004.03.009},
journal = {{Int. J. Multiphas. Flow}},
month = {jul},
number = {7-8},
pages = {995--1010},
publisher = {Elsevier {BV}},
title = {Multiphase water flow inside carbon nanotubes},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/kotsalis2004a.pdf},
volume = {30},
year = {2004}
}

  • J. H. Walther, R. L. Jaffe, E. M. Kotsalis, T. Werder, T. Halicioglu, and P. Koumoutsakos, “Hydrophobic hydration of c60 and carbon nanotubes in water," Carbon, vol. 42, iss. 5-6, p. 1185–1194, 2004.
    [BibTeX] [Abstract] [PDF] [DOI]

    We perform molecular dynamics (MD) simulations to study the hydrophobic-hydrophilic behavior of pairs Of C-60 fullerene molecules and single wall carbon nanotubes in water. The interaction potentials involve a fully atomistic description of the fullerenes or carbon nanotubes and the water is modeled using the flexible SPC model. Both unconstrained and constrained MD simulations are carried out. We find that these systems display drying, as evidenced by expulsion of the interstitial water, when the C-60 and carbon nanotubes are separated by less than 12, and 9-10 Angstrom, respectively. From the constrained simulations, the computed mean force between two carbon nanotubes in water exhibits a maximum at a tube spacing of 5.0 Angstrom which corresponds to approximately one unstable layer of interstitial water molecules. The main contribution to the force stems from the van der Waals attraction between the carbon surfaces. The minimum in the potential of mean force has a value of – 17 kJ mol(-1) Angstrom(-1) at a tube spacing of 3.5 Angstrom.

    @article{walther2004c,
author = {J.H. Walther and R.L. Jaffe and E.M. Kotsalis and T. Werder and T. Halicioglu and P. Koumoutsakos},
doi = {10.1016/j.carbon.2003.12.071},
journal = {Carbon},
month = {jan},
number = {5-6},
pages = {1185--1194},
publisher = {Elsevier {BV}},
title = {Hydrophobic hydration of C60 and carbon nanotubes in water},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/walther2004c.pdf},
volume = {42},
year = {2004}
}

2003

  • T. Werder, J. H. Walther, R. L. Jaffe, T. Halicioglu, and P. Koumoutsakos, “On the water-carbon interaction for use in molecular dynamics simulations of graphite and carbon nanotubes," J. Phys. Chem. B, vol. 112, iss. 44, p. 14090–14090, 2003.
    [BibTeX] [Abstract] [PDF] [DOI]

    A systematic molecular dynamics study shows that the contact angle of a water droplet on graphite changes significantly as a function of the water-carbon interaction energy. Together with the observation that a linear relationship can be established between the contact angle and the water monomer binding energy on graphite, a new route to calibrate interaction potential parameters is presented. Through a variation of the droplet size in the range from 1000 to 17’500 water molecules, we determine the line tension to be positive and on the order of 2 {\texttimes} 10{\^{}}-10 J/m. To recover a macroscopic contact angle of 86{\textdegree}, a water monomer binding energy of -6.33 kJ mol{\^{}}-1 is required, which is obtained by applying a carbon-oxygen Lennard-Jones potential with the parameters eps_CO = 0.392 kJ mol{\^{}}-1 and sigma_CO = 3.19 {\AA}. For this new water-carbon interaction potential, we present density profiles and hydrogen bond distributions for a water droplet on graphite.

    @article{werder2003a,
author = {T. Werder and J. H. Walther and R. L. Jaffe and T. Halicioglu and P. Koumoutsakos},
doi = {10.1021/jp8083106},
journal = {{J. Phys. Chem. B}},
month = {nov},
number = {44},
pages = {14090--14090},
publisher = {American Chemical Society ({ACS})},
title = {On the Water-Carbon Interaction for Use in Molecular Dynamics Simulations of Graphite and Carbon Nanotubes},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/werder2003a.pdf},
volume = {112},
year = {2003}
}

2001

  • J. H. Walther, R. Jaffe, T. Halicioglu, and P. Koumoutsakos, “Carbon nanotubes in water: structural characteristics and energetics," J. Phys. Chem. B, vol. 105, iss. 41, p. 9980–9987, 2001.
    [BibTeX] [Abstract] [PDF] [DOI]

    We study the structural properties of water surrounding a carbon nanotube using molecular dynamics simulations. The interaction potentials involve a description of the carbon nanotube using Morse, harmonic bending, torsion, and Lennard-Jones potentials. The water is described by the flexible Simple Point Charge (SPC) model by Teleman et al., and the carbon-water interactions include a carbon-oxygen Lennard-Jones potential, and an electrostatic quadrupole moment acting between the carbon atoms and the charge sites of the water. Vibration of the breathing mode of the carbon nanotube in water is inferred from the oscillations in carbon-carbon van der Waals energy, and the inverse proportionality between the radius of the carbon nanotube and the breathing frequency is in good agreement with experimental values. The results indicate, that under the present conditions, the presence of the water has a negligible influence on the breathing frequency. The water at the carbon-water interface is found to have a HOH plane nearly tangential to the interface, and the water radial density profile exhibits the characteristic layering also found in the graphite-water system. The average number of hydrogen bonds decreases from a value of 3.73 in the bulk phase to a value of 2.89 at the carbon-water interface. The inclusion of the carbon quadrupole moment is found to have a negligible influence on the structural properties of the water. Energy changes that occur by the process of introducing a carbon nanotube in water are calculated. The creation of a cavity in the bulk water to accommodate the nanotube constitutes the largest energy contribution. Results include an analysis of surface structure and energy values for planar and for concave cylindrical surfaces of water.

    @article{walther2001b,
author = {J. H. Walther and R. Jaffe and T. Halicioglu and P. Koumoutsakos},
doi = {10.1021/jp011344u},
journal = {{J. Phys. Chem. B}},
month = {oct},
number = {41},
pages = {9980--9987},
publisher = {American Chemical Society ({ACS})},
title = {Carbon Nanotubes in Water: Structural Characteristics and Energetics},
url = {http://www.cse-lab.ethz.ch/wp-content/papercite-data/pdf/walther2001b.pdf},
volume = {105},
year = {2001}
}