Starts 25 Sep 2019 17:00
Ends 25 Sep 2019 18:30
Central European Time
ICTP
Leonardo Building - Budinich Lecture Hall
Strada Costiera 11 34142 Trieste Italy
Prof. Bo Persson obtained his PhD in theoretical physics from Chalmers Technical University 1980. His thesis advisor was Prof. Stig Lundqvist, one of the founders of condensed matter at ICTP. He is currently working at the Peter Gruenberg Institute of the Research Center Juelich, part of Germany’s Helmholtz Association. Besides several years as a visiting scientist at IBM research laboratories, in Yorktown Heights and in Zurich, he spent numerous periods as a visiting scientist in research laboratories in Israel, Japan, China, Italy, and elsewhere. After his initial research work in dynamical processes at surfaces, he turned around 1995 to theoretical tribology (friction, adhesion, contact mechanics). He has published more that 400 articles in international journals, and is the author of "Sliding Friction: Physical Principles and Applications" (Springer, first edition 1997) and co-author (with Prof. A. Volokitin) on "Electromagnetic Fluctuations at the Nanoscale: Theory and Applications" (Springer, 2017), besides the early book (with E. Tosatti) “Physics of Sliding Friction (Kluwer 1996) collecting papers of the very first ICTP Research Workshop on the subject in 1995. Besides his primary research activity at PGI, Bo Persson is the founder and CEO of MultiscaleConsulting, a company involved in consulting (theory and experiment) on topics related to contact mechanics and friction (see www.MultiscaleConsulting.com). Most clients are from the tire industry, two F1-racing teams (rubber friction and tire dynamics), and medical companies (the contact between the rubber stopper and the barrel in syringes). Please note the Colloquium start time is 17.00 hrs. Abstract: One of the weakest forces in Nature is the van der Waals interaction which acts between all atoms and solids. Still on a macroscopic level this force field is very strong: one can theoretically hang an object with the weight of a car using a solid bar with 1 square cm cross section attached by the van der Waals interaction to a flat surface. This is never observed in reality, and in my presentation, I will explain the origin of this "adhesion paradox". I will also show how some animals, like the gecko or tree frog, have "learned" (via natural selection) to make use of these weak force fields to adhere to rough and contaminated surfaces, where traditional adhesives would fail. I will describe the origin of adhesion hysteresis, and present some experimental results illustrating it. All solid objects have surface roughness which often is fractal-like, sometimes extending from the size of the solid object to atomic distances. I will describe a theory which can be used to study the contact between two elastic solids with surface roughness and adhesion. The theory predicts the contact area and the stress probability distribution, as well as the probability distribution of interfacial separations, and is the basis for a huge number of practical applications like rubber friction, adhesion, the heat and electric contact resistance, leakage of rubber seals, conveyor belts, tire dynamics etc. It describes how the contact between two solid objects changes as the interface is studied with increasing magnification, say from the naked-eye level to atomic resolution. The theory will be illustrated with applications to the human skin, to electroadhesion for haptic touchscreens (involving the finger-glass screen contact), and adhesive pads for robotics. All are invited to attend. The talk will be livestreamed from the ICTP website. Light refreshments will be served after the event.