Seminar 1/30/09 Using the Tunable Properties of Gas Expanded Liquids to Control Nanoparticle Deposition and Separation Processes

Department of Chemical Engineering
West Virginia University

Seminar

Using the Tunable Properties of Gas Expanded Liquids to Control Nanoparticle Deposition and Separation Processes

Dr. Christopher Roberts
Department of Chemical Engineering
Auburn University
Auburn, AL

ABSTRACT

Full exploitation of nanoparticles and their novel properties for application in areas such as catalysts, optical systems, electronic devices, and sensors requires the ability to effectively process and maneuver particles onto surfaces or support structures. This is often performed by simply evaporating a liquid solution containing ligand stabilized nanoparticles to leave behind dry nanoparticles coated on a surface. However, solvent dewetting and capillary forces at the liquid/vapor interfaces can lead to film defects such as nanoparticle islands, percolating networks, ring-like particle arrays, and uneven particle concentration.

We have developed a novel particle deposition technique which utilizes carbon dioxide as an anti-solvent for low defect, wide area metallic nanoparticle film formation employing monodisperse silver, gold and other metal and semiconductor nanoparticles. Ligand stabilized nanoparticles are precipitated from organic solvents by controllably expanding the solution with carbon dioxide. Subsequent addition of carbon dioxide as a dense supercritical fluid then provides for removal of the organic solvent while avoiding the dewetting effects common to evaporating solvents. These dewetting effects and interfacial phenomena can be very detrimental to nanoscale structures. Controllable expansion of the liquid solution via CO2 injection allows for control over the thermophysical properties that govern this deposition and assembly process. This gas expanded liquid driven nanoparticle deposition process has been utilized to create thin films of nanoparticles on device surfaces, such as MEMS devices, without the detrimental interfacial dewetting effects inherent to liquid evaporation driven nanoparticle deposition techniques that would otherwise destroy these devices. Our research has shown that gold nanoparticles can be uniformly deposited onto the surfaces of polysilicon microdevices to significantly reduce adhesion and stiction.

In addition, we have extended the application of this CO2 expanded liquid deposition process to an improved method for narrowing the particle size distribution of ligand stabilized nanoparticles. Our implementation allows for the extremely easy partitioning of multiple sized, monodisperse populations almost simultaneously. We have shown that multiple monodisperse nanoparticle populations can be easily isolated from one another and from the organic solvent through controlled pressurization and deposition. Polydisperse Au, Ag and CdSe semiconductor particles (2 to 20 nm) were efficiently fractionated into +/-1nm monodisperse fractions. This tunable gas expanded liquid approach allows for rapid and efficient size separation while also reducing organic solvent usage and has been demonstrated at process scales ranging from microliters to >100 milliliters of an organic nanoparticle dispersion.

Friday, January 30, 2009 9:30am - 10:45am
Room 401, Engineering Sciences Building
Refreshments served at 9:15 am

Questions or Directions call: 304-293-2111, ext. 2418.

01/30/2009