Microdrop Generation

Eric R. Lee, Stanford University, CA.

2002

241 pages

Offers the first how-to presentation of microdrop generation, giving readers the background needed to build or evaluate complete commercial systems.
Includes the essential foundation in fluid mechanics relevant to the generation and non-image printing use of fluid microdrops
Contains extensive discussions on biological and industrial applications
Provides lists of manufacturers and suppliers of complete systems, components, and chemicals, including price lists

This bestselling reference thoroughly explores the science of miniaturization, including its methods and materials, from the historical to the state-of-the-art. For this edition, the Applications section has been expanded to provide more in-depth coverage of bio-, RF-, high-temperature, and optical MEMS. The book includes a multitude of well-chosen examples and hundreds of illustrations, many in full color.

Contents

INTRODUCTION
WHAT CAN YOU DO WITH A MICRODROP?
Characteristics of Microdrops
Use of Microdrops in Pure Science
Use of Microdrops in Applied Science
Biotechnology Applications of Microdrops
Applications in Manufacturing and Engineering
METHODS OF EJECTING MICRODROPS
Acoustically Disrupted Continuous Fluid Jet
Thermal Inkjet
Piezoelectric Direct Pressure Pulse
Focused Acoustic Beam Ejection
Liquid Spark Inkjet
Electrohydrodynamic Inkjet
Flextensional Aperture Plate Inkjet
Electro-Rheological Fluid Inkjet
Liquid Ink Fault Tolerant Process Inkjet
TopSpotÒ Microdrop Ejector
Summary and Recommendations
PARTICLE KINETICS OF EJECTED MICRODROPS
Reynolds Number and Stokes Law
Terminal Velocity
Relaxation Time Constant
Streaming
Impact
Brownian Motion
Motion in Electric Fields
ELECTRIC CHARGING OF MICRODROPS
Rayleigh Limit to Charging Microdrops
Drop Charging Mechanisms
Practical Drop Charge Control Methods
Variations in the Induced Charge
ENGINEERING REQUIREMENTS FOR RELIABLE MICRODROP GENERATION
Conditions Needed for Monodisperse Drop-On-Demand Operation
Drive Pulse Amplitude
Drive pulse Shape
Internal Pressure Level
Drop Ejection Rate
Fluid Level
Fluid Temperature
TROUBLESHOOTING DROP EJECTORS
Clogged Nozzles
Damaged Nozzles
Internal Air Bubbles
Overly Wetted Meniscus
Misdirected Jets
Internal Pressure
Insufficient Drive Amplitude
Non-Optimal Pulse Waveform
Pulse Rate
Problematic Fluid
Mechanical Mount
Imaging System
Recommended Startup Procedure for a New System
IMAGING MICRODROPS
Direct viewing of illuminated microdrops
Bright Background Imaging of Microdrops
Bright Source Stroboscopically Illuminated Droplets
Light Emitting Diode Illumination Arrays
Imaging System Synchronization
Optics
Cameras
Stroboscopic Illumination Sources
Low Cost Microdrop Imaging Hardware
DROP EJECTOR DRIVE ELECTRONICS
Gated Voltage Sources
Linear Pulse Amplifiers
FABRICATION OF EJECTION APERTURE NOZZLES
Ejection Nozzle Requirements
Fabricating Acute Edge Conical Glass Nozzles
Fabricating Tapered Profile Glass Nozzles
Micromachined Ejection Apertures
Electroformed Ejection Apertures
Jewel Orifices
Metal Optical Pinhole Apertures
Overview of Hole Generating Techniques
Anti-Wetting Surface Coatings
DROP EJECTOR CONSTRUCTION
Tubular Reservoir Piezoelectric Drop Ejectors
Metal Body Drop Ejectors
Glass, Straight Tube, Welded Aperture Plate
Glass, Pipette, Welded Aperture
Glass, Miniature, Welded Aperture
Piezoelectric Element Configuration
Piezoelectric Disc Actuator
Rectangular Slab Drive Elements
Cylindrical Piezoelectric Drive Elements
Integral Heating Elements
PRESSURE CONTROL
Manometer Tube Pressure Control System
Variable Height Reservoir Pressure Control System
Automated Pressure Control
FLUID ENGINEERING FOR MICRODROP EJECTORS
Problematic Fluids
Non-Clogging
First Drop Reliability
Jetting Stability
Directional Stability
Freedom from Satellite Drops
Wide Jet Velocity Tolerance
Drive Waveform Tolerance
Repetition Rate
Environmental and Temporal Stability
Chemical Reactivity with Drop Generator
Toxicity
Cost
COMPONENTS OF DROP-ON-DEMAND EJECTOR FLUIDS
Payload
Solvents
Humectants
Dispersants
Surfactants
Viscosity Modifiers
Polymeric Fluid Elasticity Agents
Anti-fungal Agents (Biocides, Preservatives)
Chelating Agents
pH Controllers
Corrosion Inhibitors
Defoamers
Electrical Conductivity Salts
Additives Specific for Thermal Inkjet
Additives Specific for Inkjet Image Printing
MAKING JETTABLE SUSPENSIONS OF GROUND SOLIDS
Obtaining Small Diameter Particles
Wetting and Dispersing
Filtering and Settling
Essential References
Ejectability
Final Caution - Make Sure You Have a Real Suspension
APPENDIX I. SETTING UP A MICRODROP SYSTEM ASAP
APPENDIX II. EXAMPLE INKJET FLUID FORMULATIONS FROM PATENT LITERATURE
APPENDIX III. EJECTION TESTS OF BIOLOGICAL FLUIDS