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Nano- and Microfluidics

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Figure 1: a) Separation of a Water-Hexane-Model-Emulsion on a chemically patterned surface with one side hydrophilic the other hydrophobic in a microfluidic cell. b) Using a secondary flow (Water 2) separation can be achieved faster and more efficient.

Introduction

The aim of our work is the development of a Lab on a Chip device for the separation of emulsions on chemically patterned surfaces with integrated semiconductor sensing elements. Our work is supported by the DFG priority program SPP 1164 "Nano- and Microfluidics".

The work is devided into three parts:

  1. development of chemically patterned surfaces: nanoscale hydrophobic coatings for the separation of liquid mixtures
  2. separation on chemically patterned surfaces: separation dynamics of binary liquid mixtures – theory and experiment
  3. development of a semiconductor sensor: liquid transport detection using single FET devices

Each topic is described briefly below.

1. Nanoscale hydrophobic coatings for the separation of liquid mixtures [2]

Pagra Truman*, Ralf Frenzel*, Nastasia Longari**, Petra Uhlmann*, Manfred Stamm*

*Leibniz Institute of Polymer Research Dresden, Germany; E-mail: truman@ipfdd.de; Fax:+49 (0) 351 4658281; Tel: +49 (0) 351 4658271.
**Department of Materials Science and Technology, University of Perugia, Terni, Italy; Fax: +39 (0) 744 492950; Tel: +39 (0) 744 492939

a1) Silicon substrates half covered with hydrophobic fluorosilane SAMs of thickness d and adv. contact angle θ are used for a2)  the separation of Tolune/water mixtures/beads. a3)  Due to the internal Laplace pressure difference on the hydrophobic/-philic interface water drops are driven to the hydrophilic side and merge the same time pushing the Toluene. away. b1, b2) Analogous experiment with dipcoated methacrylate coatings on silicon substrates.
Figure 2: [2] a1) Silicon substrates half covered with hydrophobic fluorosilane SAMs of thickness d and adv. contact angle θ are used for a2) the separation of Tolune/water mixtures/beads. a3) Due to the internal Laplace pressure difference on the hydrophobic/-philic interface water drops are driven to the hydrophilic side and merge the same time pushing the Toluene. away. b1, b2) Analogous experiment with dipcoated methacrylate coatings on silicon substrates.

Summary: Organofunctional silane containing coatings are widely used to modify surface chemistry and have many applications in micro- and nanofluidics because liquid motion on these scales is strongly influenced by capillary or wall effects. In this work we focus on the development of nanoscale coatings for chemically patterned surfaces using fluorosilane SAMs and fluorine containing methacrylate coatings for the novel approach to separate emulsions on surfaces with an abrupt change of wettability from hydrophilic to hydrophobic. As a model system we investigate the separation of Toluene- Water- emulsions on such surfaces and thus aim for coatings easy to apply resulting in contact angles bigger 90° the same time being solvent resistant. We study the fastness to solvents (Toluene and Acetone) as a function of the deposition parameters and demonstrate emulsion separation. The fluorosilane SAMs are patterned by combinig CVD and UV-lithography while the methacrylate coatings are deposited by dipcoating.

2. Separation dynamics of binary liquid mixtures - Theory & Experiment [3]

Pagra Truman*, Fathollah Varnik**, Petra Uhlmann*, Manfred Stamm*, Dierk Raabe**

*Leibniz Institute of Polymer Research Dresden, Germany. E-mail: truman@ipfdd.de; Fax:+49 (0) 351 4658281; Tel: +49 (0) 351 4658271.
**Max-Planck-Institut für Eisenforschung, Düsseldorf, Germany. E-mail: f.varnik@mpie.de; Fax:+49 (0) 211 6792707; Tel:+49 (0) 211 6792517

a) The separation process steps (1 = water, 2 = Toluene, 3 = hydrophilic surface, 4 = hydro-phobic surface): (a1) Laplace pressure difference induced water droplet movement to the hydrophilic surface. (a2) Water droplets coalescence due to capillary forces. (a3) The smaller drop emtpies into the bigger drop destabilizing the triple phase contact line and transferring kinetic energy. (a4, a5) flow of liquid 1 induces opposite flow of liquid 2 and vice versa . b) hydrodynamic model (grey- hydrophilic, white-hydrophobic): water only wets the hydrophilic side as long as the pressure at the interface is lower than a critical value ΔPI.
Figure 3: [3] a) The separation process steps (1 = water, 2 = Toluene, 3 = hydrophilic surface, 4 = hydro-phobic surface): (a1) Laplace pressure difference induced water droplet movement to the hydrophilic surface. (a2) Water droplets coalescence due to capillary forces. (a3) The smaller drop emtpies into the bigger drop destabilizing the triple phase contact line and transferring kinetic energy. (a4, a5) flow of liquid 1 induces opposite flow of liquid 2 and vice versa . b) hydrodynamic model (grey- hydrophilic, white-hydrophobic): water only wets the hydrophilic side as long as the pressure at the interface is lower than a critical value ΔPI.

Summary: Differences of wettability on chemically patterned surfaces allow to drive or guide liquid and even can be used to separate emulsions. It is conceivable to extend this concept to more complex systems like mixtures of multiple liquids, objects in liquids or mixtures of liquids with a higher degree of compatibility. But to do so it is necessary to understand which processes are relevant for separation and which parameters describe these processes. Using surfaces with an abrupt change of wettability and monodisperse Toluene- Water- mixtures as model emulsions we show that the separation process is a highly complex multiscale phenomena and present two theoretical approaches: On the one hand we consider the system to be a purely hydrodynamic system and transform differences of wettability into corresponding pressures. On the other hand we analyze the dynamics of single droplets. Comparing open and confined systems we find that the driving forces for separation are different.

3. Liquid transport detection using single FET devices [1],[4]

Pagra Truman, Petra Uhlmann, Manfred Stamm.

Leibniz Institute of Polymer Research Dresden, Germany. E-mail: truman@ipfdd.de. Fax:+49 (0) 351 4658281; Tel: +49 (0) 351 4658271.

The novel thin film FET Sensor. a) Image of a sensor chip with 9 integrated thin film transistor sensing elements without photoresist passivation. b) Scheme of a sensing element with materials used. c) Cross-sectional view of a sensing element indicating functional parts and electrical connections.
Figure 4: [1] The novel thin film FET Sensor. a) Image of a sensor chip with 9 integrated thin film transistor sensing elements without photoresist passivation. b) Scheme of a sensing element with materials used. c) Cross-sectional view of a sensing element indicating functional parts and electrical connections.

Summary: Observation and monitoring liquid transport and transport in liquids is a major task for lab on a chip applications and research. We use novel thin film FET devices based on silicon-on-insulator (SOI) substrates as planar sensors for the detection of liquid transport in capillaries to overcome the drawbacks of optical flow observation techniques the same time providing chemical composition analysis capabilities of ISFET technologies. Based on a newly developed theoretical model for Field-Effect liquid movement detection we demonstrate fundamental applications like the detection of capillary filling speed and level. To proof compatibility with ISFET technologies we demonstrate chemical composition analysis capabilities pH-detection and sensitivity to ionic strength. Furthermore we show how the sensitivity of the devices can be tuned as a unique feature provided by the use of silicon-on-insulator substrates.

Co-operations

  • Prof. Dr. Dierk Raabe, Dr. Fathollah Varnik
    Max-Planck-Institut für Eisenforschung, Düsseldorf
  • Prof. Dr. Jörg Weber
    Stiftungslehrstuhl für Halbleiterphyisk, Technische Universität Dresden
  • Prof. Dr. Yurii A. Shchipunov, Dr. Marina Petuhova
    Institut für Chemie an der Russischen Akademie der Wissenschaften, Wladiwostok
  • Prof. Dr. Johann Wolfgang Bartha
    Institut für Halbleiter- und Mikrosytemtechnik, Technische Universität Dresden
  • Prof. Dr. Steffen Hardt
    Leibniz Universität Hannover, Institut für Nano- und Mikroprozesstechnik
  • Dr. Magnus Jäger
    Universiät des Saarlandes, Fachrichtung Medizintechnik
  • Dr. Steffen Howitz
    GeSiM Gesellschaft für Silizium-Mikrosysteme, Großerkmannsdorf

Most important publications

Patent:

  1. Truman, P.; Uhlmann, P.; Stamm, M.
    Sensor für die Bestimmung der Fließbewegungen von und/oder in Flüssigkeiten sowie seine Verwendung
    DE 10 2005 030 200.9.52, IPF Dresden

Paper:

  1. Truman, P.; Uhlmann, P.; Stamm, M.
    Monitoring liquid transport and chemical composition in lab on a chip systems using ion sensitive FET devices mehr
    Lab on a Chip 6 (2006) 1220-1228

  2. Drechsler, A.; Petong, N.; Bellmann, C.; Busch, P.; Stamm, M.; Grundke, K.; Reichelt, J.
    The Effect of Adsorbed Cationic Surfactant on the Pattern Collapse of Photoresist Lines in Photolithographic Processes mehr
    Progress in Colloid and Polymer Science 132 (2006) S 82-94

Recommended Publications


  • Hoy, O.; Zdyrko, B.; Lupitskyy, R.; Sheparovych, R.; Aulich, D.; Wang, J.; Bittrich, E.; Eichhorn, K.-J.; Uhlmann, P.; Hinrichs, K.; Müller, M.; Stamm, M.; Minko, S.; Luzinov, I.
    Synthetic hydrophilic materials with tunable strength and a range of hydrophobic interactions mehr
    Advanced Functional Materials 20 (2010) 2240-2247


  • Truman, P.; Uhlmann, P.; Frenzel, R.; Stamm, M.
    A stack of functional nanolayers for simultaneous emulsion separation and sensing mehr
    Advanced Materials 21 (2009) 3601-3604


  • Varnik, F.; Truman, P.; Wu, B.; Uhlmann, P.; Raabe, D.; Stamm, M.
    Wetting gradiend uínduced separation of emulsions: A bomcined experimental and lattice Boltzmann computer simulation study mehr
    Physics of Fluids 20 (2008) 072104


  • Truman, P.; Uhlmann, P.; Stamm, M.
    Monitoring liquid transport and chemical composition in lab on a chip systems using ion sensitive FET devices mehr
    Lab on a Chip 6 (2006) 1220-1228


  • Uhlmann, P.; Ionov, L.; Houbenov, N.; Nitschke, M.; Grundke, K.; Motornov, M.; Minko, S.; Stamm, M.
    Surface functionalization by smart coatings: stimuli-responsive binary polymer brushes mehr
    Progress in Organic Coatings 55 (2006) 168-174


 
Nano- and Microfluidics
Nano- and Microfluidics

Departments

Nanostructured Materials

Fields of Research

Intelligent surfaces with polymer brushes