Experimental Condensed-Matter Physics
Itai Cohen
Assistant Professor of Physics
508 & C7 Clark Hall
Cornell University
Ithaca, New York 14853
(607) 255-0815
(607) 255-8853 (lab)
B.S., Physics, 1995, University of California at Los Angeles. Ph.D., Physics, 2001, University of Chicago. Post-doctoral Associate, Physics and Division of Engineering and Applied Science, Harvard University, 2001-2005. Assistant Professor, Physics, Cornell University, 2005 - present.
Research Areas
Investigating how incorporating structure into fluids at various length scales affects their macroscopic flow properties. The systems we investigate include Newtonian fluids, liquid crystals, colloidal suspensions, insect wings, and bio-polymer networks. While these materials are ubiquitous and can be found in any kitchen, understanding their out-of-equilibrium behavior and non-linear response to applied stresses remains one of the biggest challenges in Physics.
Current Research
It is an exciting time to study complex fluids. We are now living out what was merely science fiction in past decades. Whether it's using shear thickening colloidal suspensions to design flexible yet bullet proof protective gear, or using protective polymer shells that rupture on command to make drug delivery devices, the message is clear: Designing adaptable materials whose optical and rheological properties can be tuned through their response to various stimuli including shear, electromagnetic fields, acoustical vibrations, and confinement will have a profound effect on our society.
Developing such materials requires a fundamental understanding of the design principles linking the incorporation of structure into fluids and the resulting fluid properties. My lab is focusing on four areas at the forefront of this broad field:
Colloidal suspensions – where microscopic and nanoscopic particles or sheets are suspended in a fluid.
Bio-polymer networks – where the properties of natural and artificial tissues comprised of cross-linked polymer networks are investigated.
Fluid-fluid and fluid-membrane interfaces – where fluid flows interact with an interface or flexible membrane. The air flows induced by insect wings are an example of such an interaction.
Liquid-crystals – where the fluid molecules themselves have structure.
Learning the design principles on each of these length scales will lead to fabrication of hybrid materials sensitive to combinations of stimuli and flow configurations. These novel materials will be used to engineer the next generation of products ranging from car seat cushions to lubricants to biological implants.
Confocal Rheometer
One of our main goals is to develop instruments and techniques for simultaneous imaging of the material structure and measurement of its flow properties. To this end, we have built a shear cell which can be loaded onto a confocal microscope. This device allows us to simultaneously image the 3-D structure of a fluorescent material such as a colloidal suspension or biopolymer network while measuring the amount of force necessary to shear the material. In this way, the link between material structure at the micron scale and the material properties at the macroscopic scale can be investigated quantitatively.
Lab Philosophy
More generally, our lab philosophy is to construct the particular experiment needed to investigate the physics problem at hand. As such, we often rely on interactions with experts from other physics, chemistry, and engineering groups both here at Cornell and at other institutions. This style of research allows us to learn the techniques we need to use at a rapid pace, and creates an engaging and intellectually stimulating environment for our work.
Postdocs
John Savage and Xiang Cheng
Graduate Students
Mark Buckley, Sharon Gerbode, Leif Ristroph and John Mergo
Undergraduate Students
Dan Porter and Svetlana Morozova