Research

Artificial Reconfigurable Materials: structural dynamics and functions

Based on our core of imaging and understanding structural dynamics, we work on three types of systems, each offering complementary and distinct insights into how materials evolution pathways determine their functional performance.

Emergence of Order from Nanoparticle Ensembles:  We have been pushing a paradigm to study the organization dynamics of shape-anisotropic nanoparticles in liquids. Nanoparticles are chosen as the focus of study because they have unique potentials for miniaturization, exhibit rich size-defined properties, both individually and coupled, and have interactions that are difficult to model due to nonadditivity and multiscale-coupling effects. We integrate minimally-invasive low-dose liquid-phase TEM with our image analysis code suites to extract mechanistic understandings of the nanoparticle‒nanoscale interaction‒organization relationship. Representative work in this direction:

Kim, Jones, Ou, Chen, ACS Nano 10, 9801, 2016:  Our foundational work that measured and calibrated beam effects on nanoparticle assembly by correlating liquid-phase TEM imaging with small angle X-ray scattering.

Kim, Ou, Jones, Song, Chen, Nat. Commun. 8, 761, 2017: Our first work on imaging 2D assembly dynamics of anisotropic nanoparticles from solution into linear chains, which follows quantitative laws and concepts in step-growth molecular polymerization.

Luo, Smith, Ou, Chen, Acc. Chem. Rev. 50, 1125, 2017: Our review paper on the emerging field of integrating in-situ TEM movies, single particle tracking, statistical mechanics analysis and theoretical modeling to understand the organization rules at the nanoscale.

Ou, Wang, Luo, Luijten, Chen, Nat. Mater. 2019: First work to resolve the crystallization pathways of nanoparticles into 3D superlattices, charting a non-classical nucleation pathway involving amorphous intermediate.   

Morphogenesis in Polymeric Materials: We find that much like how living cells undergo morphogenesis in organism formation, polymers develop into distinct 3D morphologies to determine their performances, under stress/temperature gradient in synthesis or external geometric confinement. A prominent example we worked on since 2016 is the polymer separation film used for water purification, which has intricate 3D crumples with nanoscale features on the surface grown from interfacial polymerization. We use low-dose EM tomography to acquire the 3D structures of inner void and outer surface of crumples at nanometer resolution and develop a potent morphometry analysis method for extracting features from the 3D structure, which all tie back to the uneven interfacial fluctuations in synthesis. The demonstrated “triangular” crosstalk among synthesis, 3D nanoscale morphology and performance can serve as a new framework for predictive design of separation materials. Another emerging direction in the group is to investigate how such morphogenesis couples with other interfaces, such as on curved nanoparticle surfaces. Representative work in this direction:

Kim, Zhou, Yao, Ni, Luo, Sing, Chen, J. Am. Chem. Soc. 141, 11796, 2019: Our first work to engineer and utilize morphological features of polymers redefined by a curved nanoparticle surface.

Song, Smith, Kim, Zaluzec, Chen, An, Dennison, Cahill, Kulzick, Chen, ACS Appl. Mater. Interfaces 11, 8517, 2019: Our first work to map the 3D inner structure and surface morphology of crumples in a polyamide membrane establishing the protocols of EM tomography imaging and morphometry analysis. 

Nanostructured Materials and Molecular Reactions: Beyond mere structure elucidation, we also concern how nanostructured materials restructure and affect molecular reactions. Our focus is to develop correlative characterizations bridging morphology imaging and molecular level detection to build a comprehensive understanding of the structure‒property relationship. Representative work in this direction:

Chen, Zhan, Luo, Ou, Shih, Yao, Pidaparthy, Patra, An, Braun, Stephens, Yang, Zuo, Chen, Nano Lett. 19, 4712, 2019: Our first work to discover and trace size-dependent phase transition pathways as Mg ions intercalate into cathode materials for applications in rechargeable Mg ion batteries.