Xiang Cheng

Associate Professor

Contact Information

Email: xcheng@umn.edu

Phone: 612/624-6165

Faculty website: https://www.cems.umn.edu/people/faculty/xiang-cheng

Education

B.S., Physics, Peking University, 2002

Ph.D., Physics, The University of Chicago, 2009

Postdoc, Physics, Cornell University, 2012

Awards

Arthur B. Metzner Early Career Award, Society of Rheology, 2019

DARPA Young Faculty Award, 2016

3M Non-Tenured Faculty Award, 2016

McKnight Land-Grant Professorship, 2016-2018

Packard Fellowship, 2015

NSF CAREER Award, 2015

Grainger Fellowship, 2006

Gaurang and Kanwal Yodh Prize, 2006

Research Interests

We study soft materials physics in experiments, with a special focus on the emergent flow behaviors of soft materials and their mesoscopic structural origins. Research in soft materials has had a profound impact on our society. The invention of liquid crystal displays (LCD), the development of e-ink used in Kindles via charged colloidal particles, and the potential use of shear-thickening suspensions to “top kill” disastrous blowout in oil wells are just a few examples that highlight the fascinating applications of soft materials. In each case, the underlying mechanism is governed by the unique structures of soft materials on mesoscopic length scales between the molecular and the macroscopic. These mesoscopic structures can readily respond to stimuli such as weak electromagnetic fields, shear, acoustic vibrations or even thermal fluctuations. Thus, understanding the interplay between mesoscopic structures of a soft material and its bulk material properties, as well as controlling structural transitions through external forces, becomes the key for advancing our soft material research.

Our study concentrates on three forefront areas of soft material research. (1) Sheared colloidal suspensions and biological fluids. By employing various methods such as confocal microscopy, holographic imaging and rheometry, we study flow properties of suspensions composed of micron/nano-scale particles; We also investigate the shear-induced dynamics of biological fluids such as suspensions of swimming bacteria. (2) Granular flows with applications to geological problems. Using the state-of-art high-speed imaging techniques for discrete granular particles and fluid flows, we investigate granular flows in avalanches and under shear. We apply our lab-scale experiments to the understanding of emergent patterns in the geo-scale of natural granular flows. (3) Glass/jamming transition of soft materials. Large classes of materials ranging from simple glass-forming liquids, polymer melts, to even shaving foams, show a similar transition between a flowing fluid-like state and a disordered solid state. These transitions in different systems can be unified with the generic jamming phase diagram. By developing a novel setup, “confocal rheoscope”, which couples a confocal microscope to a mechanically deformable cell, we investigate the effect of mechanical perturbations on the jamming transition. The goal of our research is to control and furthermore to design soft materials with desirable material properties, based on the understanding of their mesoscopic or microscopic structures.

Xiang Chneg