Micro-evaporators for kinetic exploration of phase diagrams

We use pervaporation-based microfluidic devices to concentrate species in aqueous solutions with spatial and temporal control of the process. Using experiments and modelling, we quantitatively describe the advection-diffusion behavior of the concentration field of various solutions (electrolytes, colloids, etc) and demonstrate the potential of these devices as universal tools for the kinetic exploration of the phases and textures that form upon concentration

Extracting the hydrodynamic resistance of droplets from their behavior in microchannel networks

The overall traffic of droplets in a network of microfluidic channels is strongly influenced by the liquid properties of the moving droplets. In particular, the effective hydrodynamic resistance of individual droplets plays a key role in their global behavior. We here propose two simple and low-cost experimental methods for measuring this parameter by analyzing the dynamics of a regular sequence of droplets injected into an "asymmetric loop" network. The choice of a droplet taking either route through the loop is influenced by the presence of previous droplets which modulate the hydrodynamic resistance of the branches they are sitting in. We propose to extract the effective resistance of a droplet from easily observable time series, namely from the choices the droplets make at junctions and from the inter-droplet distances. This becomes possible when utilizing a recently proposed theoretical model, based on a number of simplifying assumptions. We here present several sets of measurements of the hydrodynamic resistance of droplets, expressed in terms of a "resistance length". The aim is twofold, (1) to reveal its dependence on a number of parameters, such as the viscosity, the volume of droplets, their velocity as well as the spacing between them. At the same time (2), by using a standard measurement technique, we compare the limitations of the proposed methods. As an important result of this comparison we obtain the range of validity of the simplifying assumptions made in the theoretical model.Comment: 11 pages, 11 figure

A microfluidic device for investigating crystal nucleation kinetics

We have developed an original setup using microfluidic tools allowing one to produce continuously monodisperse microreactors ($\approx 100$ nL), and to control their temperatures as they flow in the microdevice. With a specific microchannels geometry, we are able to apply large temperature quenches to droplets containing a KNO$_3$ solution (up to 50$^{\circ}$C in 10 s), and then to follow nucleation kinetics at high supersaturations. By measuring the probability of crystal presence in the droplets as a function of time, we estimate the nucleation rate for different supersaturations, and confront our results to the classical nucleation theory

Elasticite, plasticite et fusion des cristaux colloiedaux sous cisaillement

SIGLECNRS T 54557 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Outils microfluidiques pour l'étude des processus de cristallisation (solubilité, polymorphisme et cinétique de nucléation)

Ce travail porte sur la réalisation de systèmes microfluidiques pour l étude de processus de cristallisation. Le but est de rendre plus rapide et plus simple l acquisition de données expérimentales sur la cristallisation, essentielles pour les industries chimiques et pharmaceutiques. L ensemble des outils est basé sur un contrôle précis des températures et sur la production et la manipulation de gouttes d une centaine de nanolitres dans des systèmes microfluidiques. Ces gouttes sont utilise es comme microréacteurs indépendants dans lesquels il est possible d induire la formation de cristaux dans des conditions contrôlées. Par ailleurs, les différents systèmes s appuient sur la possibilité d observer un grand nombre de gouttes pour réaliser des criblages de conditions opératoires et accéder à des données statistiques sur des phénomènes stochastiques tels que la nucléation. Le premier système permet d'effectuer des criblages rapides de diagrammes de solubilité de soluté dans un solvant. Le second dispositif permet de détecter les formes polymorphiques d un composé qui se forment lors de l étape de cristallisation, et les deux derniers ont pour but de mesurer des cinétiques de nucléation. Le faible volume des gouttes est un point crucial dans ces dispositifs. En effet, dans de tels volumes, il est possible d atteindre des sursaturations élevées, d induire la nucléation mononucléaire et par conséquent, d isoler les cristaux formés. Grâce à ces outils, nous avons pu entre autre, mesurer pour la première fois la limite de solubilité d une forme métastable du nitrate de potassium, et mettre en évidence l importance des impuretés lors du processus de nucléation.This work deals with the development of microfluidic devices for studying crystallization processes. The goal is to simplify and to increase the speed of experimental data acquisition on crystallization, which is important for chemical and pharmaceutical industries. The devices are based on a precise temperature control and on the production and manipulation of hundreds of nanoliter-sized droplets in specific microfluidic systems. The droplets are used as independent microreactors in which we can induce crystal formation in a controlled way. Besides, since the different systems offer the possibility to observe directly a large number of droplets, they enable us to perform high-throughput screening of experimental conditions and to carry out statistical measurements of stochastic phenomenon such as nucleation. The first device was developed for the rapid screening of solubility diagrams. The second one enables us to detect polymorphic forms of a compound appearing during a crystallization step, and the two last systems are used to measure nucleation kinetics. The small droplet volume is crucial for these applications. Indeed, in such a small volume, it is possible to reach very high supersaturations, to induce mononuclear nucleation and as a consequence, to separate all nucleation events. Thanks to these microfluidic tools, for the first time we measured the solubility limit of a metastable form of potassium nitrate, and show the importance of impurities in crystal nucleation process.BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Processing of temperature field in chemical microreactors with infrared thermography

This work is devoted to the first analysis of temperature fields related to chemical microfluidic reactors. The heat transport around and inside a microchannel is both convective and diffusive with spatial distribution of source terms and strong conductive effects in the channel surrounding. With simplified assumptions, it is shown that Infrared thermography and processing methods of the temperature frames allow to estimate important fields for the chemical engineers, such as the heating source distribution of the chemical reaction along the channel. A validation experiment of a temperature field processing method is proposed with Joule effect as calibrated source term and non reactive fluids. From such previous experiment, a Peclet field is estimated and used in a further step in order to study an acid-base flow configuratio

Rheological measurements on a microfluidic device

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