Peter Hoffman
When a liquid is not a liquid: The mysteries of nanoconfined fluids
Liquids confined in nanoscale spaces play an important role in biology, nanscale electr-mechanical devices (NEMS), and nanotribology. When liquids are confined at the nanoscale they exhibit surprising structural and dynamical properties not observed in the bulk. The observed behavior ranges from spontaneous solidification to observed suppression of freezing temperatures (i.e. the exact opposite), depending on the nature of the liquid and the confining geometry and surface structure. I will present some ‘historical’ experiments and show why this area of research has created so much interest and controversy.
At Wayne State University, we recently build a new type of Atomic Force Microscope (AFM) which can measure the stiffness and dynamical damping parameter of any liquid confined between the AFM tip and a flat surface. We found some very surprising behavior, including a ‘kinetic’ phase transition between liquid and solid depending on how fast the liquid was squeezed between the tip and the surface. I will give an introduction to our new AFM, describe what makes it better than other AFM’s and present some of our most recent and most puzzling results. I will also give some examples of other research that will be possible with this new type of AFM, ranging from the exploration of biomolecular systems to nanotribology.
Biography:
Dr. Peter Hoffmann did his undergraduate studies in Physics and Mathematics at Technical University Clausthal, Germany. In 1994 he received a M.S. in Physics from Southern Illinois University, in Carbondale. His research at SIU was in the area of phase transformation in nano-confined fluids. From 1994-1999 he was a research student in the Materials Science Department at Johns Hopkins University under the guidance of Prof. Peter C. Searson, where he completed with a Ph.D. on the ‘Surface Science at the Silicon/ Liquid Interface”. Part of his research at Johns Hopkins involved Scanning Probe Microscopy with semiconductors in liquids. Based on this experience, he was hired by John Pethica at University of Oxford to work as a research fellow with the newly developed Atomic Force Microscope, studying its use in vacuum and in liquids. This work alone lead to almost 10 publications. In 2001, he was hired in the Physics Department at Wayne State University and has since built up a research group focusing on novel AFM techniques and measurements in ultra-high vacuum and in liquids. Particular areas of interest are atomic/ molecular manipulation, nano-confined liquids, and nanomechanics of biological systems.
