Speakers

Bio : Pierre Colinet is a Research Director of the Fonds de la Recherche Scientifique (FNRS) and Professor at the Ecole Polytechnique of the Université Libre de Bruxelles, where he heads the Fluid Physics Research Unit within the TIPs (Transfers, Interfaces and Processes) laboratory. He currently teaches Physical Chemistry and Modeling of Multiphase Systems, and his main research interests are in capillarity, wetting, surface-tension-driven flows, phase change (e.g. evaporation and boiling), heat/mass transfer, thin films and droplets, pattern formation, nonlinear dynamics, micro- and nano-fluidics, …

This lecture will summarize some recent progresses in understanding the dynamics of partially or completely wetting sessile drops of volatile liquids, the contact line of which being free to advance by spreading or recede by evaporation. First, as moving contact lines are inherently associated with the well-known divergence of the viscous stress, some theoretical approaches enabling its relaxation are presented, in parallel with the corresponding resolution of the evaporation flux singularity. Second, a recent asymptotic theory of evaporating sessile droplets is outlined, focusing on the possibility of reducing the overall dynamics to a simple coupled system of two ODE’s for the radius and volume. Then, experimental results (mostly based on Mach-Zehnder interferometry) and interpreting theories are presented about: i) the values of apparent contact angles induced by evaporation, due to intense microflows occurring near the contact line; ii) the effect of buoyancy-induced convection in the gas phase, due to the vapor being heavier than air (here for a pendant droplet); iii) the influence of the thermal Marangoni effect on the shape of thin droplets evaporating into air; iv) the competition between spreading and evaporation of droplets deposited on structured substrates (square arrays of cylindrical pillars).

Acknowledgements

The author gratefully thanks co-authors of the presented work, namely A. Rednikov, S. Dehaeck, Y. Tsoumpas N. Savva, L. Mekhitarian, B. Sobac, and B. Haut. Financial support of ESA, BELSPO, and Fonds de la Recherche Scientifique – FNRS is also acknowledged.

Bio : Petra Dittrich is Associate Professor for Bioanalytics at the Department of Biosystems Science and Engineering at ETH Zürich, Switzerland, since 2014. Her research in the field of lab-on-chip-technologies focuses on the miniaturization of high-sensitivity devices for chemical and biological analyses, and microfluidic-aided organization of materials.

She studied chemistry at Bielefeld University (Germany) and Universidad de Salamanca (Spain) from 1993 to 1999. She earned her PhD degree at the Max Planck-Institute for Biophysical Chemistry (MPI Göttingen, Germany) in 2003. After another year as postdoctoral fellow at the MPI Göttingen, she had a postdoctoral appointment at the Institute for Analytical Sciences (ISAS Dortmund, Germany) (2004-2008). From 2008-2014, she was Assistant Professor at the Organic Chemistry Laboratories of the Department of Chemistry and Applied Biosciences (ETH Zurich). For research stays, she visited the Cornell University (Ithaca, USA, in 2002) and the University of Tokyo (Japan, in 2005).

Petra Dittrich received the Starting Grant from the European Research Commission (ERC) in 2008, and the ERC Consolidator Grant in 2016. She was awarded the Analytica Forschungspreis of the German Society of Biochemistry and Molecular Biology (GBM), donated by Roche Diagnostics GmbH in 2010 and the Heinrich Emmanuel Merck award, donated by Merck KGaA, in 2015.

Conductive nano- and microwires are very promising sensing elements. In the past years, various approaches to form such wires have been presented. However, most of them are based on reactions in bulk with little control on the reaction conditions of individual wires, and require post-processing such as purification. In addition, it is still challenging to integrate the created structures into a functional analytical device. Recently, we showed the advantage of microfluidic devices for the creation of nanowires made of metal organic compounds or coordination polymers (1-4). We exploited the laminar flow conditions providing a well-defined interface between two streams (1,2), or used small reaction volumes to allow defined diffusion of the precursors (3).
Here, we demonstrate an improved microchip design for the site-specific formation of single nano- and microwires, where we exploit the increased permeability of the microchip substrate poly(dimethyl)siloxane (PDMS) for organic molecules after swelling caused by an organic solvent. In these devices, two adjacent, but still fully separated microchannel systems are filled with the precursor solutions HAuCl3 and TTF in acetonitrile, respectively. Swelling of PDMS by acetonitrile enables the diffusion of TTF towards the HAuCl3 solution, where the redoxreaction to AuTTF takes place yielding extraordinary long wires of several hundred micrometers. The geometry of the channels provides physical constraints with respect to number, orientation and localization of the created wires.
We utilized such wires for sensing gases and in addition, we successfully achieved the functionalization of nanowires for sensing biomolecules (5). Binding of dopamine to the functionalized wires could be detected by using Raman spectroscopy. Moreover, we showed in a proof-of-concept experiment that we could immobilize antibodies on the nanowires to enable the binding and detection of analytes with a high specificity. Future work focuses on the realization of conductivity measurements for sensing biomolecules.

(1) J. Puigmarti-Luis, D. Schaffhauser, B. R. Burg, P. S. Dittrich, Adv. Mat. 22 (2010), 2255-2259.

(2) Y. Xing, N. Esser, P. S. Dittrich, J. Mat. C 4 (2016), 9235-9244.

(3) B. Cvetkovic, J. Puigmarti-Luis, D. Schaffhauser, T. Ryll, S. Schmid, P. S. Dittrich, ACS Nano 7 (2013), 183-190.

(4) J. Puigmarti-Luis, M. Rubio-Martinez, U. Hartfelder, I. Imaz, D. Maspoch, P. S. Dittrich, J. Am. Chem. Soc. 133 (2011), 4216-4219.

(5) Y. Xing, A. Wyss, N. Esser, P. S. Dittrich, Analyst 140 (2015), 7896-7901.

Bio : Alejandro L. Garcia is a professor in the Department of Physics and Astronomy at San Jose State University and a participating guest in the Center for Computational Sciences and Engineering at Lawrence Berkeley National Laboratory. Dr. Garcia's research is in stochastic simulations for fluid and statistical mechanics. He is the author of the textbook Numerical Methods for Physics and a physics consultant for film and gaming studios.

All devices that operate at mesoscopic scales, from microelectromechanical systems (MEMS) to biological membranes, function in chaotic conditions due to thermal fluctuations. Surprisingly, hydrodynamic transport models (e.g., Navier-Stokes equations) are often still accurate at these scales for which spontaneous fluctuations are significant. A well-known example is the hydrodynamic prediction of the spectral features of light scattering, such as Rayleigh scattering that makes the sky blue. New interesting phenomena appear in non-equilibrium systems, such as the "giant fluctuation" effect, which is an enhancement of diffusion during mixing due to the correlation of velocity and concentration fluctuations.

Direct Simulation Monte Carlo (DSMC) simulations are useful in the study of hydrodynamic fluctuations due to their computational efficiency and ability to model molecular detail, such as internal energy and chemical reactions. More recently, stochastic finite volume schemes based on the fluctuating hydrodynamic equations of Landau and Lifshitz have been formulated and validated by comparisons with DSMC simulations. This talk discusses some of the important fluctuation phenomena investigated using DSMC and stochastic Navier-Stokes simulations, including examples of fluid mixtures with reactive and charged species.

Bio : Robert Ellefson is a physicist with experience in vacuum science, gas analysis, instrument design and product manufacturing. He earned a BS in Physics at St Olaf College, a MS in Physics at the University of Illinois and a PhD in physics at the University of Wyoming as a Bureau of Mines Fellow in Laramie, WY, USA. Dr Ellefson spent 22 years at the Mound DoE laboratory in Miamisburg, OH where he focused on the design and operation of high vacuum systems, tritium-handling systems, mass spectrometer-based tritium gas analysis systems and tritium inventory measurement methodology all related to fusion and nuclear weapons applications. Following retirement from Mound in 1994, he consulted at Los Alamos National Laboratory for two years. In 1996 he began managing and working with the quadrupole mass spectrometer (QMS) sensor group at INFICON, Inc. in Syracuse NY to design and develop instruments for semiconductor process monitoring. Key products developed include a high-pressure QMS for direct operation on physical vapor deposition processes and a compact process monitor with closed ion source to monitor chemical vapor deposition and etch processes as well as more benign processes. He retired a second time in January 2005 after 9 years at INFICON. Currently Dr. Ellefson is a consultant (REVac Consulting) with various national and international laboratories, manufacturers and other industries using knowledge based on forty nine years of experience with many types of mass spectrometers, gas analysis and vacuum technology. In 2011 The American Vacuum Society named him AVS Fellow for key applications of quadrupole mass spectrometers for vacuum process monitoring and for developing new Recommended Vacuum Practices for AVS.

Manufacturing and laboratory processes typically have changing compositions. To sample such processes involves the transport of a representative sample of the process gas to a gas analyzer. In the sampling process there is the bulk flow of the gas plus the wall interaction as the composition changes. Models will be presented for the gas flow of each species in a mixture of gases at its process pressure and a model for conditioning the surface of the transport channel. Specific examples for water vapor will be presented. Where useful, time constants for the transport delay and conditioning time are developed. Examples of results from process sampling of various semiconductor and other processes will be given. These include physical vapor deposition, wafer degassing, fuel cell exhaust analysis, atomic layer deposition, chemical vapor deposition, fluorocarbon etch. Results from a scanning mass spectrometer sampling probe for plasma etch will also be presented.

Bio : Eugenia Kumacheva received her undergraduate degree and M.Sc. degree in The Technical University (Saint Petersburg) and her Ph.D. degree in Physical Chemistry of Polymers (Russian Academy of Sciences). She was Minerva Foundation Postdoctoral Fellow at the Weizmann Institute of Science. In 1996, she joined the University of Toronto as an Assistant Professor and was promoted to the ranks of Professor in 2005. She was Visiting Professor at the Universities of Cambridge, Oxford and Harvard, Moscow State University, Universitè Louis Pasteur and the University of Bayreuth. Since 2006, she is Canada Research Chair in Advanced Polymer Materials (Tier 1).

Among her awards are Killam Fellowship, Macromolecular Science and Engineering Award, Clara Benson Award (CIC), Schlumberger Scholarship (U.K.), International Chorafas Foundation Award in Physics and Engineering (Switzerland), Humboldt Research Award (Germany), Canada Chemical Society Medal (2017 and the 2009 L'Oreal-UNESCO Award “For Women in Science” (given to 5 laureates in the world). She is a University Professor, the University of Toronto, the highest distinction in recognition scholarly excellence, given to <2% of Faculty of the University. She is a Fellow of the Royal Society of Canada and Royal Society (U.K.).

Eugenia Kumacheva's public service includes her work in the Macromolecular Science and Engineering Division (NSERC Canada), Vanier-Banting Selection Board (NSERC Canada), and National L’Oreal-Unesco “Women in Science” selection committee. She is an editor or on advisory boards of several scientific journals. She serves on Science Foundation review panels for U.S.A., Ireland, Germany, the Netherlands, Israel and Switzerland. She serves on scientific advisory boards for the Waterloo Nanoscience Institute (Canada), Triangle Materials Science Center and Brookhaven National Laboratory (USA), RIKEN Institute (Japan), Freiburg Institute for Advanced Studies and Max Planck Institute for Polymer Research (Germany), Leibnitz Institute (Germany), international review panel for the L'Oreal-Unesco Award and the European Union Science Council and membership of the member of the New Fellows Sectional Committee of the Royal Society (UK).

Gas-liquid reactions and physical processes involving carbon dioxide (CO2), one of the most important green house gases, are of great practical and fundamental importance. To reduce CO2 emission and generate new, efficient catalysts and optimized chemical formulations for CO2 sequestration, fundamental knowledge has to be developed on the mechanisms of gas-liquid reactions, their kinetic and thermodynamic characteristics and physical CO2-related processes, e.g., extraction and phase separation. Current methods to study reactions of CO2 are challenging, due to the mass-transfer limitation and a poorly defined interface between the gas and liquid phases.

We developed several microfluidic platforms that utilize the generation of the uniformly sized CO2 bubbles in the liquid reactive medium and subsequent analysis of the time-dependent changes in bubble dimensions. We present the applications of these platforms for direct and reversed reactions of CO2 with amines and Frustrated Lewis pairs, as well as for studies of physical processes such as liquid-liquid extraction and phase separation mediated by CO2 reactions.