OSC Colloquium: Daniel Ou-Yang

    Thursday, April 18, 2019 - 3:30pm - 5:00pm
    Meinel 307

    1630 E. University Blvd.

    3rd Floor Lobby area


    Open to campus and public.


    Speaker: Daniel Ou-Yang

    Topic: Optical tweezers: applications of colloidal force spectroscopy to study soft matter physics

    Hosted by: Masud Mansuripur

    Visit our website for future lecture dates and speaker information: http://www.optics.arizona.edu/news-events/events/colloquium For a list of our archived lectures: http://www.optics.arizona.edu/news-events/events/colloquium/archive


    This talk is an attribution to celebrate Arthur Ashkin’s 2018 Nobel Prize in Physics "for the optical tweezers and their application to biological systems. The talk tells how optical tweezers were developed into colloidal force spectroscopy (CFS), a method broadly applicable for the study of colloids and soft matter physics problems. How CFS works are explained by two examples of such studies, one of a living system and the other a mimicked living system. In the first example, the story tells how micromechanical properties of the interior of a living cell can be measured with minimal invasiveness; the experimental study includes the probing of the viscoelasticity of the interior of the cell, the fluctuation-dissipation relationship of the mechanical noises in the living cell, and how, from these active, non-thermal noises, one could deduce non-linear and non-equilibrium mechanical properties of the living cell. The second example starts by asking the question “suppose the microscopic objects expelled from pollens that were observed in 1827 by Robert Brown were alive, how could he tell and what could have been learned by just observing the particles”. To address this question, a model active Brownian particle (ABP) system comprising micron-sized metallic Janus particles were synthesized. The ABP are active because they can be driven into ballistic translation with controlled speed, and these particles can turn due to their intrinsic thermal rotational diffusion.  By varying the ratio of the ballistic vs rotational motion, one could tune their activity (or liveliness) and investigate how their non-thermal activity could be quantified, and how the use of “effective temperatures” as a measure of such system’s activity breaks down. The talk concludes by a video showing the ABPs phase separate into coexisting phases of clusters and free individual particles - a surprise, considering the system comprises purely repulsive particles.

    Speaker Bio(s): 

    Professor H. Daniel Ou-Yang received B.S. and M.S. in physics from Fu-Jen Catholic University in Taiwan and Ph.D. in physics from UCLA. He did postdoctoral research at the University of Pennsylvania and the Exxon Corporate Research Laboratory. He joined the faculty of the Physics Department of Lehigh University in 1988 and is now a Professor of Physics and Bioengineering. He is also the Director of the Emulsion Polymers Institute at Lehigh. During his academic leaves from Lehigh Ou-Yang served as a visiting professor at University of Strasbourg, Hong Kong University of Science and Technology, National Taiwan University, Korea Advanced Institute of Science and Technology, Beijing University of Chemical Technology, and University of Bordeaux. Ou-Yang leads a research group in experimental soft matter and biological physics at Lehigh University.


    Refreshments 3:30pm


    Lecture @ 3:45pm - 5pm