Research at LMTP

Listen to Dr. Daniel Attinger presenting his views on research (March 2009) "(click on his name left from the movie panel)"

We want to understand and control transport phenomena at the microscale, in the presence of interfaces. In other words, we consider the transport of energy and fluids in geometries with a typical size of a few microns. Such small geometries offer an ideal playing field for micro-drops and micro-bubbles, because surfaces forces like wetting and Laplace forces win over bulk forces like gravity. For instance, heat transfer between a molten microdroplet and a solid surface is heavily controlled by the imperfect thermal contact between the droplet and the solid surface.  Also, the motion of bubbles in microchannels depends strongly on wetting forces. Once this complex interplay of interfacial forces is understood, we want to engineer surfaces and geometries to put drops and bubbles to work, to perform tasks in cooling, manufacturing and bioengineering with extreme reliability and precision. The best example of a bubble at work is seen in ink-jet printing, where the explosive growth of a micro-bubble is exploited to generate micro-bubbles with a high precision.

To understand transport phenomena at the microscale, we typically try to develop high-resolution measurements method and match them with numerical simulations, which we also develop. This approach is illustrated by the following projects:

• "Coupling the High Resolution of Laser Measurements and Finite-Element Simulations to Understand Transport Phenomena during Microdroplet Deposition". We look at the heat transfer between an impacting drop with high-speed visualization, a proprietary Finite-Element code and a novel interfacial laser measurement method. Our strategy is to compare laser temperature measurements with Finite-Element simulations and high-speed visualization: this will allow the investigation of process and material parameters controlling interfacial heat transfer.

• Bubble rebound against a solid wall. This three-phase proble We investigate the lubrication flow generated during the rebound of a bubble against a solid surface with high-speed visualization and a proprietary Finite-Difference code. There is still a lack of comprehensive modeling of this phenomenon that spans several time and space scales, and the problem has application in manufacturing of chemicals, high-performance cooling and drag reduction.

• We investigate the transport of a bubble in a microchannel using high-speed visualization and pressure measurements. We identify strategies to prevent bubbles to clog microchannels, a problem of interest for microfluidics and bioengineering.

• Acoustic excitation of superharmonic capillary waves on a gas-liquid meniscus

To control transport phenomena at the microscale, we use microheaters, droplet generators, pressure controllers and actuators, and micromachined geometries. This approach is illustrated by the following projects:

• Controlled bubble microstreaming in microgeometries. Using a shear flow created in the immediate vicinity of an oscillating microbubble in a confined geometry, we control the motion of biological cells and can even power a micro-rotor at a speed of 500 revolutions per minute. Such an approach will allow the manufacturing of rotary actuators that can be fitted into a space as thin as a human hair.

• Drop or Bubble on demand in a microfluidic chip

Applications of our research are in:

• non-traditional manufacturing
• heat management (e.g. computer cooling)
• environmental aerosol radiative properties measurements
• environmental remediation
• bioengineering
• microfluidics

The news page presents our funding sources. Please have a look at our publications and at the gallery.