Our research theme is to understand the organization of complex materials and biological systems in space and time. The specific systems and the associated relevance we concern are wide-ranging and ever-expanding, from ion-oxide intercalation in batteries, crumpled polymer films for water filtration, phase-changing nanoparticle ensembles as adaptive devices, ion channels gating cells, to amyloid fibril prevention for curing disease. These efforts, despite the remoteness of topics, are all unified by one common framework: deciphering fundamental rules of organization from “seeing is believing”, to resolve the dynamics of the constitutes. The implementation of this framework draws on our unique expertise in direct in-situ imaging, particularly our efforts on the groundbreaking liquid-phase transmission electron microscopy (TEM) that resolves the structure and dynamics of nanoscale entities in a suspending media. Such experiment data have been previously elusive; thus, they have the sheer power to fill critical gaps in condensed matter physics, materials science, therapeutics and biophysics, when coupled with the toolkit and concepts in deep learning, mathematics, and statistical mechanics.

Hope to see the most up-to-date progress of our research? Come and join our weekly group meetings starting from 1 pm on Wednesdays in Room 1005 at Supercon! See the group meeting schedule here.

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.


Structural Biophysics of Proteins: transformation mechanism studies via nanoscopic imaging

We foresee great opportunities in resolving and understanding the fundamental nanoscopic structuring and functioning mechanisms of proteins, in various biological states and in a dynamically-modulated surrounding liquid media. We push the technical boundaries of TEM imaging for both single protein level imaging of shape transformation as well as the collective behaviors of many proteins interacting with each other such as disease-causing protein fibrils. Our long-term goal is to forge the field of structural biophysics, where the experimentally mapped nanoscale structures inform seamlessly the dynamics and physical behaviors of biological systems. Representative work in this direction:

Smith, Jiang, An, Barclay, Licari, Tajkhorshid, Moore, Rienstra, Moore, Chen, ACS Appl. Nano Mater. 2019: Our first work to decipher polymer assisted disassembly pathways of amyloid fibrils through fragmentation and lateral association.