Ruobing Bai


Ruobing Bai is an Assistant Professor in the Department of Mechanical and Industrial Engineering at Northeastern University. He received his BS in Theoretical and Applied Mechanics at Peking University in 2012, and PhD in Engineering Sciences at Harvard University in 2018. He was a postdoctoral fellow in the Department of Mechanical and Civil Engineering at California Institute of Technology from 2018 to 2020. Research in the Bai group aims to combine theory and experiment in solid mechanics, soft active materials, large deformation, fracture and adhesion, multiphysics, and instability of materials. Applications include soft machines and robots, sustainable materials, human health, human-machine interfaces, human augmentation, and biohybrid machines. Bai is a long-term fan of NEWMech and was the recipient of the NEWMech Best Poster Award at MIT in 2017.

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Talk : Mesoscale photomechanical coupling in photoactive materials

Some molecules can absorb light of a certain wavelength and change their shape, dissociate, or combine to form new molecules. The photoactive materials made from these molecules are capable of large deformation or mechanical work output upon light illumination, inspiring new applications of photomechanical machines. However, compared to an individual photoactive molecule, existing photoactive materials at the macroscale perform much poorer in their actuation efficiency and work output, severely limiting their application in real scenario. This contrast highlights an urgent research need for mechanistic understanding of photomechanics at the mesoscale (e.g., micrometer) that bridges a nanoscale molecule and a macroscale material. This talk will present our recent progress in such fundamental understanding of mesoscale photomechanical coupling in photoactive liquid crystal elastomers, semicrystalline polymers, and molecular crystals. Using statistical and continuum theoretical frameworks, we investigate the three-way photomechanical coupling between light propagation, photoreaction, and mechanics. When embedded in a solid, photoactive molecules do not react independently, but behave collectively through various long-range interactions, leading to interesting phenomena including tunable molecular alignment, photomechanical phase transformation, formation of microstructure, instability, and their consequences in the macroscopic material actuation.