(7hu) Imaging the Structure and Dynamics of Soft Materials

Soft materials are ubiquitous in our daily life with examples ranging from plastics in the manufacturing sector to particle suspensions in cosmetic, food and medical products. Although soft materials exhibit a wide range of fascinating characteristics, they share a few common organizing principles that arise from their unique mesoscopic structures. Thus, the key to advance soft materials research is to understand the interplay between mesoscopic structures and macroscopic properties of soft materials and, furthermore, to realize controls over the assembly of these mesoscopic structures. Current state-of-the-art microscopy techniques allow us to image the mesoscopic structures of various soft materials under different external stimuli with unprecedented spatiotemporal resolutions, providing the direct link between structures and material properties. Within this exciting context, I would like to establish an experimental program, where I will employ various cutting-edge imaging tools to investigate the structural origin of different soft-material properties and explore the structural transformation of soft materials under external stimuli.

Specifically, my research focuses on phase transitions in colloids and the transport dynamics of active fluids. In my PhD work, I combined video microscopy with a new local heating technique, which allows me to explore the kinetics of phase transitions in colloidal crystals and study the influence of confinement and external flows on the nucleation. The results from my research reveal the nucleation mechanisms at single particle scales and are insightful for materials engineering. In my postdoctoral work with Prof. Xiang Cheng, I studied the transport and rheology of active fluids and explore the onset kinetics of the swarming motion of active fluids. These studies deepen our understanding on transport processes in microbiological systems and provide new insights on the emergent collective behaviors of active fluids.

In my future research plan, I will focus on soft materials out of equilibrium. These include the self-assembly and phase transitions of colloidal suspensions under external fields, glassy dynamics and glass transition of colloidal suspensions, and transport and rheology of active matter. I will combine the video microscopy and rheology/microrheology techniques to understand the detailed dynamics of these nonequilibrium processes. Furthermore, I aim to apply the understanding in practical applications such as coating process, bacterial infection, biomedicine and design of smart materials.

Postdoctoral project: Collective dynamics of bacterial suspensions. Department of Chemical Engineering and Materials Science, University of Minnesota, under supervision of Xiang Cheng.

PhD Dissertation: Phase transitions in thin-film colloidal crystals. Department of Physics, Hong Kong University of Science and Technology, under supervision of Yilong Han.

Selected Publication:

1. Yi Peng, Wei Li, Feng Wang, Tim Still, Arjun G. Yodh, and Yilong Han, Diffusive and martensitic nucleation kinetics in solid-solid transitions of colloidal crystals, Nature Communications, 8, 14978 (2017).
2. Yi Peng, Lipeng Lai, Yishu Tai, Kechun Zhang, Xinliang Xu and Xiang Cheng, Diffusion of ellipsoids in bacterial suspensions, Physical Review Letters 116, 068303 (2016) (Highlighted by Editors’ Suggestion).
3. Yi Peng, Feng Wang, Ziren Wang, Ahemd Alsayed, Zexin Zhang, Arjun Yodh and Yilong Han, Two-step nucleation mechanisms in solid-solid phase transitions, Nature Materials, 14, 101–108 (2015). (Focus Article with Cover Image)
4. Yi Peng, Ziren Wang, Ahemed Alsayed, Arjun Yodh and Yilong Han, Melting of colloidal crystal films, Physical Review Letters 104, 205703 (2010) (featured by Physical Review Focus)

Teaching Interests:

My teaching philosophy rests on the belief that education is not the filling of a pail, but the lighting of a fire. Teaching is not only about conveying facts or techniques written in textbooks, it is also about showing students how we can tackle new problems using the knowledge and skills we already have. I was a teaching assistant for Fundamentals of Physics, Electrical and Magnetism, Energy and Environment and the related laboratory courses in my graduate study. I have also mentored several graduate and undergraduate students. In the future, I would like to teach Thermodynamics and Statistical mechanics, Fluid Mechanics and Rheology classes, as well as to develop new courses on Soft Materials