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Projects

P1 Transport of water through single nanotubes #CNRS

Objectives:

Our main objective is to perform experiments on fluid and ion transport inside individual nanotubes under diverse forcing (electric fields, pressure drops, etc.). The influence of the confining materials is a key question; we will compare carbon (CNT) and boron-nitride (BNNT) nanotubes with the same structure but different electronic properties. Recent results demonstrate that BNNTs generate huge electric currents under salt gradients, which will be explored in the context of sustainable energy harvesting (“blue energy”). Composite materials combining suprafriction properties of CNT and electrokinetic power of BNNT will be explored, as well as transport across graphene and h-BN molecular sheets. Novel nanofluidic devices like osmotic diodes or ion pumps will be designed.

Expected Results:

  • In-depth understanding of fluid transport through individual nanotubes and through an array of nanotubes • Creation of composite-material nanotubes with unique properties
  • Prototype nanofluidic devices: osmotic diodes and ionic pumps

Contact:

Lydéric Bocquet

email

P2 Control of molecular transport by electric fields and mechanical force #UCAM

Objectives:

We will investigate transport of colloids through nanochannels driven by electric fields and mechanical pressure. The nanochannels will be fabricated by a novel technique based on focussed-ion-beam deposition of Pt wires (developed by the applicant) allowing for creation of channels with varying cross section. Single particles will be imaged with high-speed video detection and manipulated by holographic optical tweezers. In addition, we aim to controllably change the surface of the nanochannels by attaching polyethylene-glycol (PEG) molecules that are linked to positively charged poly-l-lysine chains, which will allow an unprecedented control of the force and translocation speed in the channels. Furthermore, PEG coating will control both the screening of the surface charges and the hydrodynamic boundary conditions for ion movement. We will extend this work to the transport of macromolecules (DNA, proteins). By measuring ionic current and force at the same time, we will map out the complete potential of molecular interactions in nanochannel and provide the first quantitative data on this process.

Expected Results:

  • A novel lab-on-a-chip system with complete control of boundary conditions and nanoparticles in nanofluidic applications
  • Understand the relation between molecular interactions and transport of nano-confined colloids
  • Single-macromolecule characterization based on analysis of translocation of DNA/proteins through nanochannels

Contact:

Ulrich Keyser

email

P3 Novel techniques for electrokinetic measurements in colloidal suspensions #COR

Objectives:

Today measuring colloidal charge/electrophoretic mobility of nanoparticles in suspension remains a challenge in many circumstances: low electrophoretic mobility samples, high concentration samples, high conductivity medium, etc. In order to circumvent these limits, we propose to investigate theoretically and experimentally a new highly sensitive optical technique based on Differential Phase Optical Low Coherence Tomography (DP-OCT). After a first step of bibliographic research, the candidate will thoroughly study the theory and physical principles of DP-OCT in order to determine accessible performances of this technique.  In parallel, an experimental work will be started with the assembly of a DP-OCT set up in Cordouan’s lab.  The candidate will systematically explore sensitivity, reproducibility, concentration range, spatial resolution, applied voltage, and detection volume of the experimental system. The performances of DP OCT will then be compared with Laser Doppler Electrophoresis (LDE) developed in Cordouan and acoustophoresis technique developed at the PHENIX-UPMC lab. At a final stage we will collaborate with other nodes (CNRS, JÜLICH, UZH) to demonstrate the capability of the system to perform high-resolution electrophoretic mobility measurements in various colloidal suspensions: weakly charged colloids, concentrated suspensions, nonpolar and low dielectric constant solvent, etc.

Expected Results:

  • A fully functional prototype system for measuring single-particle mobility based on DP-OCT technique
  • Novel insights into the electrophoretic behaviour of colloids based on measurements with the new system

Contact:

David Jacob

email

P4 Shear of ionic nano-films between graphene sheets #University of Oxford

Objective:

The objective of this project is to discover the structure and dynamic properties of ionic electrolytes confined to nano-films between atomically smooth carbon (graphene) plates. The experimental setup will involve modification of a standard Surface Force Apparatus (SFA) to graft large graphene sheets (0.25 cm2) onto standard mica substrates. Electrical connections to graphene sheets will provide control of the surface potential. We will study pure ionic liquids and highly concentrated salts in organic solvents (propylene carbonate or acetonitrile). Methodology for creating the graphene electrode-surfaces is developed in the group, already as a working prototype. This reduces the risk of this otherwise highly innovative experiment: to our knowledge no similar experiment has yet been constructed using graphene/graphite surfaces.

Expected Results:

  • A novel experimental setup for exploration of fluid shear flow in atomistic detail
  • Understand viscous and shear flow properties of the electrolytes in nanoconfinement for different ionic liquid type

Responsibilities/duties: The ESR will undertake a research project in the research team of Professor Susan Perkin in the Physical and Theoretical Chemistry Laboratory. The project will involve detailed experimental measurements of the interaction force between two parallel graphene sheets, both in air and with fluids confined between. Static (equilibrium) and dynamic forces will be of interest. The experimental work will be analysed and interpreted by engagement with theory and simulation studies in collaborating laboratories. The ESR will also have general responsibilities in the laboratory, such as laboratory management, project planning and presentation of results.

Contact:

Susan Perkin

email

P5 Multiscale modelling of electrokinetics in nanoconfinement #FUB

Objectives:

Multiscale modeling of electrokinetic flow is challenging due to the coexisting length- and timescales and materials heterogeneity at the nanoscale, which requires flexibility in dealing with boundary conditions. Our main objective is to develop theoretical tools and methods to quantitatively predict the transport of fluids and ions inside nanotubes and nanocavities in electric fields. The influence and the interplay of interfacial dielectric and viscosity profiles, which will be extracted from atomistic MD simulations, are central issues. We will import these profiles into coarse-grained models and make quantitative predictions of the electrokinetic flow and the conductivity in nanochannels for various ions, channel size and surface functionalities. In particular, we will consider carbon (CNT) and boron-nitride (BNNT) nanotubes in order to make explicit contact with the experiments done in the consortium. In previous work, we have shown that atomistic simulations can correctly reproduce the surface capacitance of water, which is a prerequisite for a correct treatment of electrokinetic effects. For all biological and solid surfaces, the electrokinetic surface charge is found to be substantially lower than their bare surface charge, which is traditionally rationalized by an enhanced interfacial viscosity. However, the surface conductivity is substantially higher than expected based on the electrophoretic mobility, which is explained by the awkward assumption of an excess surface conductivity. Experimental capacitance, electrophoretic and conductivity studies can be explained and brought into harmony by the interplay of interfacial dielectric and viscosity profiles as extracted from atomistic MD simulations. How such molecular details allow tuning the transport efficiency in nanotubes is a key question, with strong potential impact on energy production and storage applications.

Expected Results:

  • A computer program for coarse grained simulations based on atomistic input that can be used by experimental groups
  • Prediction for electrokinetic flow and conductivity as a function of driving field, surface characteristics of the nanotubes and nanocavities, type and concentration of ions.

Contact:

Roland Netz

email

P6 Water interfaces under shear flow from ab initio molecular dynamics simulations #Johannes Gutemberg Universitaet Mainz

Objectives:

This project will move beyond the current exploited approaches by investigating nonequilibrium water interfaces with ab initio molecular dynamics simulations that do not rely on any fitted parameters. The central question we want to address is how different the water structure and dynamics is in nanochannels under shear flow with respect to equilibrium conditions. We will develop models where the full electronic structure details are included in order to understand how the interactions at the solid/liquid interface affect water dynamics, including water reorientation and hydrogen bond dynamics. We want to achieve molecular understanding of water properties in confinement as a function of wall electronic properties, pH and ionic strength. We will compare simulations to standard force field approach, e.g. SPCE water model, and develop a newly parameterized force field that is capable of reproducing ab initio properties under shear flow (we will be following the force matching scheme). The project has a fundamental as well an applied component. It will provide plenty of information on water properties in interfacial shear flow that will serve as an input for several other NANOTRANS projects. Moreover, the results of this project will be of interest for understanding various other types of nanochannels, e.g. those occurring in zeolites and metal organic framework materials (MOFS).

Expected Results:

  • Microscopic understanding of water properties in nanoconfinement as function of the wall electronic properties
  • Explain experimental observations (ESR1) of water transport through standard CNTs and boron-nitrite nanotubes
  • A newly parameterized atomistic force field suitable for studying the flow of confined water under shear

Contact:

Marialore Sulpizi

email

P7 Electro-acoustics in nanocolloidal suspensions and nanopores #CNRS

Context

In 1933, Debye predicted that an acoustic wave travelling through a fluid containing charged solutes should create an electric field. This effect has been measured a few years later, and was called the acoustoelectric effect. Despite its relationship to well known electrokinetic phenomena such as electrophoresis, there is a growing interest in using such effect as a means to investigate the properties of nanoparticles, both in suspension or under confinement in a porous material. This size range, between molecular ions and colloidal particles, remains a great challenge for the theory and modelling of electro-acoustic effects.

Objectives:

The objective of this project is therefore to develop a multiscale theoretical approach to study both electrophoresis and electroacoustic transport phenomena by combining atomistic simulations (MD) and mesoscopic simulations. This numerical approach should have the ability to link the microscopic characteristics of the systems with high precision values of the transport coefficients, or related dynamical quantities. Nanoparticles, such as Keggin ions, well adapted to electroacoustic measurements, will be studied by equilibrium (Kubo formalism) and non-equilibrium MD.  Relevant properties on the nanometer scale will allow to derive coarse-grained models for mesoscopic simulations. Once the mesoscopic models and simulation techniques have been validated for these small nanoparticles, these models will be used for both bigger colloidal particles and for nanoparticles under confinement. For particle and pore sizes in the tens of nm range, e.g. for iron oxide nanoparticles or nanofluidics, resort to mesoscopic models will provide the appropriate compromise between computational efficiency and account of the coupled hydrodynamic and electric phenomena, including the effect of thermal fluctuations.

Expected Results:

  • Hybrid multiscale method combining MD and mesoscopic methods to study acoustoelectric effects
  • Framework to quantitatively analyse electroacoustic measurements beyond idealized assumptions
  • Exploration of high-frequency regimes to date not reachable by electroacoustic devices

Contact:

Marie Jardat, Benjamin Rotenberg

email

P8 Modelling transport of soft confined nano-colloids #University of Cambridge

Objectives:

We will use computer simulations to study the electrokinetic flow and electrophoretic mobility of soft deformable nanocolloidal particles driven by external electric fields. We will combine efficient methods for calculating electrostatic potentials in equilibrium (Poisson-Boltzmann solver based on successive over-relaxation for monovalent electrolyte) with mesoscopic Lattice Boltzmann scheme to treat fluid and charge flow. The first goal is to understand the polarization of the electrolyte medium around charged particles in an external DC field resulting in effective multipolar interactions among the particles. We will particularly focus on polarization effects in confinement, e.g. in nanochannels or near the walls and corners. This is tightly connected to experimental projects (ESR2 and ESR5). The role of particle deformability will be investigated by combining the described methods with an elastic model for soft colloids. Finally, we will explore the role of electrokinetic effects in polyelectrolyte brushes / nanoparticle mixtures.

Expected Results:

  • Hybrid computational method for exact electrostatic profiles combined with fluid flow
  • Theoretical understanding of electrolyte polarization around charged colloids in external fields and in confinement
  • Observation of novel phenomena due to coupling of particles’ deformability to the electrokinetic flow

Contact:

Jure Dobnikar

email

P9 Dynamics of ionic condensates in colloidal dispersions #CNRS Paris

Objectives:

The statistical physics of charged macromolecules runs afoul of intuition in several respects. A noteworthy illustration is provided by the attraction between similarly charged surfaces that may set in under strong enough Coulombic couplings. The like-charge attraction ensuing is the key effect underlying a wealth of phenomena, including DNA compaction, some scenarios of colloidal aggregation, and the cohesion of cement pastes. Ionic condensates are important mediators to these phenomena. They are also paramount for more weakly coupled systems, where they govern the effective interactions between colloidal bodies. The goal of this PhD is to study, by analytical and computational tools, the dynamics for the formation of these condensates. An emphasis will be put on the geometry of the colloids considered, such as the locally cylindrical shape relevant for DNA. A good command of statistical physics, a taste for theoretical physics and a curiosity for experiments will be welcome.

Expected Results:

  • Theoretical understanding of the dynamics of counterion condensation on DNA
  • Molecular dynamics simulations of ion correlations in weak and strong coupling regimes
  • Relation between electric correlations and liquid-solid friction in micro-fabrication techniques

Contact:

Emmanuel Trizac

email

P10 Driven Nematic Colloids for reconfigurable self-assembly #University of Barcelona

Objectives:

Our main objective is to obtain a new composite material made of dispersed colloids embedded in an active elastic matrix. The latter will be prepared from a system of bundled microtubules internally sheared by clusters of ATP-fueled kinesin motors. While volume-like preparations lead to the assembly of an active gel, the two-dimensional system shows nematic-like textures permeated by streaming flows. Adding colloids, one may expect to open two completely unexplored avenues. Our first goal is to look for trends of actively-driven colloidal assembly, mediated by the large-scale organized textures and flows of the active material. On the other hand, possibilities to control the latter are envisaged by using conveniently functionalized entities that could be intimately incorporated, and not only dispersed, on the active matrix.

Expected Results:

  • Preparation of composite materials, sol- or emulsion-like, made of active filamentary proteins and dispersed colloids
  • Analysis of strategies of assembly and control.

Contact: 

Francesc Sagues

email

P11 Modelling phoretic effects #University of Cambridge

Objectives:

The Unilever/Cambridge team aim to provide training of ESRs in the modelling of phoretic effects. Particularly, we aim to be able to predict the magnitude of phoretic coefficients on the basis of atomistic simulations. To do this we will build on classical theories of phoresis, and we will develop the necessary atomistic and mesoscale simulation methods. The project will initially consider uncharged solutes. As surface-active materials are usually charged, it will become important to consider electrophoretic and streaming potential effects at a later stage.

Expected Results:

  • A novel hybrid atomistic/mesoscale method to simulate the phoretic phenomena
  • Determination of phoretic coefficient in diffusiophoresis
  • Understanding the effect of electrophoretic and streaming potential

Contact:

Daan Frenkel

email

P12 Transport and instabilities of binary mixtures under confinement #University of Barcelona

Objectives:

We will analyse the implications of wetting to control driven binary mixtures flow in confined geometries like porous media, and to destabilize fluid fronts and study their potential to generate drops and emulsions in micro and nanofluidics. We will also analyse the role of electrolyte transport under confinement and its implications in dynamic wetting including the effects of external electric fields as a complementary tool to control fluid flow and promote instabilities in forced fluid interfaces in confinement. As the dimensions of devices are decreased, thermal fluctuations have an increasingly important effect on fluid kinetics. We will explore the interplay of thermal fluctuations and dispersion forces. Numerical simulations will be based on a flexible scheme, which accounts for hydrodynamics and for the differential solubility of the electrolyte for the two immiscible fluids, which will allow exploring on the same footing the interplay between the relative affinity of the electrolyte and the forced wetting of fluid interfaces in complex geometries.

Expected Results:

  • A novel simulation approach combining hydrodynamics and differential solubility of fluid components
  • Understand the flow of driven binary mixtures in porous materials
  • Predict the stability of droplets and emulsions in nanofluidic devices

Contact:

Ignacio Pagonabarraga

email

P13 Transport of semiflexible polymers through structured nanochannels #Forschungszentrum Ju?lich

Objectives:

Theoretically understand transport properties of semidilute solutions of semiflexible polymers confined in structured nanochannels with periodically varying cross-section. Such flow geometries are closely related to polymer translocation through nanopores. We will apply a hybrid simulation approach combining MD simulations of polymers with the multiparticle collision dynamics (MPC) method for the fluid53. We will study the flow of a single polymer in a narrow structured channel and explore how the transport properties and polymer deformation vary with the chain stiffness. This knowledge will be useful for controlling the flow in nanochannels and nanochannel networks. In wider channels, interactions between polymers become important at finite polymer concentrations. For example, polymers of different molecular weight move with different velocities. We will investigate such cooperative transport with special interest in the competition between (length-dependent) migration of polymers across streamlines, the entropic repulsion by neighbouring chains, and flow-induced focusing. DNA molecules are highly charged, but the charges are strongly screened under physiological conditions. Such polyelectrolytes can be exposed to a combination of fluid flow and electric field, which provides an additional control of their migration properties in channels. Here, Coulomb and hydrodynamic interactions as well as polymer deformation in the flow field determine the transport properties.

Expected Results:

  • Understanding the transport properties and conformations of a single polymer in a narrow structured nanochannel
  • Understanding cooperative polymer transport through nanochannels and nanochannel networks
  • Predicting the effects of external electrical field and rational design of nanochannels with specific target properties

Contact:

Gerhard Gompper

email

P14 Transport of ring polymers in microfluidic channels #Universitaet Wien

Objectives:

Our main objective is to quantitatively analyze the properties of pressure-driven flow of polymers with no free ends (ring polymers) through smooth and structured microfluidic and nanofuidic channels. We will take full account of monomer-monomer interactions and bond-uncrossability constraints, as well as of hydrodynamic interactions by employing suitable hybrid simulation schemes, i.e. Stochastic Rotation Dynamics (SRD). The objectives are to understand the conformations, diffusion and relaxation of ring polymers under flow, to quantify the ways in which the topology of a closed loop affects the same and differentiates them from linear chains, and to take proper account of the role of knots on transport through narrow and patterned channels.

Expected Results:

  • Understand the diffusion, relaxation and transport properties of unknotted ring polymers in narrows channels
  • Model knotted polymers and explain the effect of the topology on transport
  • Design of nanofilters that separate rings with different knotedness

Contact:

Christos Likos

email

P15 Molecular transport and dynamics in particle based colloidal gels #UNILEVER Research and Development Vlaardingen B.V

Objectives:

We will investigate solvent and particles dynamics in particle-structured soft matter systems. The role of solvent evaporation and/or migration on the rheological behaviour and stability will be investigated in gels structured with colloidal particles. The structure and dynamic non-equilibrium states will be studied in respect to phenomena such as spreading and deposition on soft and hard (biological and synthetic) substrates, rheology (i.e. shear thinning and structure rejuvenation) and phase stability (i.e. syneresis, integrity of a single gel-like phase or formation of shear gel particles). The kinetics of solvent evaporation will determine nanoscale dimensions in the particle gels. We will study dynamic re-arrangement of single particles and particle network, concentration gradients that can trigger diffusiophoresis or gel contraction, and the effect of fluid and particle dynamics on the coupling of mechanical stresses between gel and soft substrates and interfaces (e.g. oil-water interfaces in emulsions). Electrostatic correlations are particularly important in systems with high ionic strength in the presence of multivalent ions and polyelectrolytes. These interactions can be strongly influenced by solvent composition, which will be explored within this project as well. Finally, the generated in-depth understanding of colloidal phase behaviour in particle-based gels is expected to trigger tremendous development of new materials and applications (e.g. personal and household care products) that will constitute the final part of our project.

Expected Results:

  • Performed systematic exploration of solvent evaporation kinetics and dynamic particle arrangement in different conditions
  • Development of new materials for advanced personal and household products

Contact:

Krassimir Velikov

email