My research interests have been focusing on how individual building blocks come together resulting in complex functions which are hard to predict, if possible, from the individual identities. Similar to a digital screen displaying a movie, the complicated pattern and story can hardly be interpreted from the dynamic traces of a single pixel. Specifically, I have been studying the general topic of self-assembly and non-equilibrium behaviors in soft matter systems, using both experimental and simulation tools.
I obtained my B.S. degree in physics from University of Science and Technology of China (USTC) in 2015. In my undergraduate research, I tried to use computer simulation to study multiple systems in Prof. Zhonghuai Hou’s group, such as the Viscek model for self-propelled particles. In 2014, I visited Oxford University to study the phase behaviors of active nematics using Lattice-Boltzmann method in Prof. Julia M. Yeomans' group. In 2020, I obtained my Ph.D. degree in Materials Science and Engineering at University of Illinois at Urbana-Champaign (UIUC) under the supervision of Prof. Qian Chen. During my Ph.D. research, we illustrated the nonclassical crystallization pathway of nanoparticles (Nat. Mater., 19, 450–455, 2020) and supracrystal growth kinetics (Nat. Commun., 11, 4555, 2020) using liquid-phase TEM. I also studied other nonequilibrium behaviors in novel colloidal systems, such as shape transformation of metal-organic framework crystals during chemical etching (ACS Appl. Mater. Interfaces, 10, 48, 40990–40995, 2018), application of ferromagnetic colloids in inductor design (Science Adv., 6, 3, eaay4508, 2020; US Patent App. 16/434,524) and electron transport in redox-active colloids.
In August 2020, I joined Prof. Guosong Hong’s group at the materials science and engineering department at Stanford University to develop novel nanomaterials that can interact with neurons at the subcellular level. Armed with the knowledge of nanotechnology and theoretical modeling, we are extending the tools that can be used to investigate the challenging questions in neuroscience.
Honors & Awards
Racheff-Intel Award, UIUC (2020)
Conference Travel Awards for Grdaduate Students, UIUC (2019)
Dow Best Presentation Award for Soft Materials Seminar, UIUC (2019)
Outstanding Teaching Assistant Award, USTC (2015)
Ph.D., University of Illinois at Urbana-Champaign, Materials Science and Engineering (2020)
B.S., University of Science and Technology of China, Physics (2015)
Revealing Structure Properties of ZIF-8 Particles Prepared by Wet Chemical Etching via 3D Electron Tomography
ACS Materials Letters
2021; 3: 171–178
View details for DOI 10.1021/acsmaterialslett.0c00398
Nanoscopic morphological effect on the optical properties of polymer-grafted gold polyhedra
View details for DOI 10.1039/D1NA00035G
Kinetic pathways of crystallization at the nanoscale
2020; 19 (4): 450-+
Nucleation and growth are universally important in systems from the atomic to the micrometre scale as they dictate structural and functional attributes of crystals. However, at the nanoscale, the pathways towards crystallization have been largely unexplored owing to the challenge of resolving the motion of individual building blocks in a liquid medium. Here we address this gap by directly imaging the full transition of dispersed gold nanoprisms to a superlattice at the single-particle level. We utilize liquid-phase transmission electron microscopy at low dose rates to control nanoparticle interactions without affecting their motions. Combining particle tracking with Monte Carlo simulations, we reveal that positional ordering of the superlattice emerges from orientational disorder. This method allows us to measure parameters such as line tension and phase coordinates, charting the nonclassical nucleation pathway involving a dense, amorphous intermediate. We demonstrate the versatility of our approach via crystallization of different nanoparticles, pointing the way to more general applications.
View details for DOI 10.1038/s41563-019-0514-1
View details for Web of Science ID 000521751700020
View details for PubMedID 31659295
Monolithic mtesla-level magnetic induction by self-rolled-up membrane technology.
2020; 6 (3): eaay4508
Monolithic strong magnetic induction at the mtesla to tesla level provides essential functionalities to physical, chemical, and medical systems. Current design options are constrained by existing capabilities in three-dimensional (3D) structure construction, current handling, and magnetic material integration. We report here geometric transformation of large-area and relatively thick (~100 to 250 nm) 2D nanomembranes into multiturn 3D air-core microtubes by a vapor-phase self-rolled-up membrane (S-RuM) nanotechnology, combined with postrolling integration of ferrofluid magnetic materials by capillary force. Hundreds of S-RuM power inductors on sapphire are designed and tested, with maximum operating frequency exceeding 500 MHz. An inductance of 1.24 muH at 10 kHz has been achieved for a single microtube inductor, with corresponding areal and volumetric inductance densities of 3 muH/mm2 and 23 muH/mm3, respectively. The simulated intensity of the magnetic induction reaches tens of mtesla in fabricated devices at 10 MHz.
View details for DOI 10.1126/sciadv.aay4508
View details for PubMedID 32010770
Nonclassical Crystallization Observed by Liquid-Phase Transmission Electron Microscopy
Crystallization via Nonclassical Pathways
American Chemical Society. 2020: 115–146
View details for DOI 10.1021/bk-2020-1358.ch006
Imaging how thermal capillary waves and anisotropic interfacial stiffness shape nanoparticle supracrystals.
2020; 11 (1): 4555
Development of the surface morphology and shape of crystalline nanostructures governs the functionality of various materials, ranging from phonon transport to biocompatibility. However, the kinetic pathways, following which such development occurs, have been largely unexplored due to the lack of real-space imaging at single particle resolution. Here, we use colloidal nanoparticles assembling into supracrystals as a model system, and pinpoint the key role of surface fluctuation in shaping supracrystals. Utilizing liquid-phase transmission electron microscopy, we map the spatiotemporal surface profiles of supracrystals, which follow a capillary wave theory. Based on this theory, we measure otherwise elusive interfacial properties such as interfacial stiffness and mobility, the former of which demonstrates a remarkable dependence on the exposed facet of the supracrystal. The facet of lower surface energy is favored, consistent with the Wulff construction rule. Our imaging-analysis framework can be applicable to other phenomena, such as electrodeposition, nucleation, and membrane deformation.
View details for DOI 10.1038/s41467-020-18363-2
View details for PubMedID 32917872
"Colloid-Atom Duality" in the Assembly Dynamics of Concave Gold Nanoarrows.
Journal of the American Chemical Society
2020; 142 (27): 11669–73
We use liquid-phase transmission electron microscopy (TEM) to study self-assembly dynamics of charged gold nanoarrows (GNAs), which reveal an unexpected "colloid-atom duality". On one hand, they assemble following the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory for colloids when van der Waals attraction overruns slightly screened electrostatic repulsion. Due to concaveness in shape, GNAs adopt zipper motifs with lateral offset in their assembly matching with our modeling of inter-GNA interaction, which form into unconventional structures resembling degenerate crystals. On the other hand, further screening of electrostatic repulsion leads to merging of clusters assembled from GNAs, reminiscent of the coalescence growth mode in atomic crystals driven by minimization of surface energy, as we measure from the surface fluctuation of clusters. Liquid-phase TEM captures the initial formation of highly curved necks bridging the two clusters. Analysis of the real-time evolution of neck width illustrates the first-time observation of coalescence in colloidal assemblies facilitated by rapid surface diffusion of GNAs. We attribute the duality to the confluence of factors (e.g., nanoscale colloidal interaction, diffusional dynamics) that we access by liquid-phase TEM, taking turns to dominate at different conditions, which is potentially generic to the nanoscale. The atom aspect, in particular, can inspire utilization of atomic crystal synthesis strategies to encode structure and dynamics in nanoscale assembly.
View details for DOI 10.1021/jacs.0c04444
View details for PubMedID 32543864
- Charting the quantitative relationship between two-dimensional morphology parameters of polyamide membranes and synthesis conditions MOLECULAR SYSTEMS DESIGN & ENGINEERING 2020; 5 (1): 102–9
Nanoscale Cinematography of Soft Matter System under Liquid-Phase TEM
Accounts of Materials Research
View details for DOI 10.1021/accountsmr.0c00013
Machine Learning to Reveal Nanoparticle Dynamics from Liquid-Phase TEM Videos.
ACS central science
2020; 6 (8): 1421–30
Liquid-phase transmission electron microscopy (TEM) has been recently applied to materials chemistry to gain fundamental understanding of various reaction and phase transition dynamics at nanometer resolution. However, quantitative extraction of physical and chemical parameters from the liquid-phase TEM videos remains bottlenecked by the lack of automated analysis methods compatible with the videos' high noisiness and spatial heterogeneity. Here, we integrate, for the first time, liquid-phase TEM imaging with our customized analysis framework based on a machine learning model called U-Net neural network. This combination is made possible by our workflow to generate simulated TEM images as the training data with well-defined ground truth. We apply this framework to three typical systems of colloidal nanoparticles, concerning their diffusion and interaction, reaction kinetics, and assembly dynamics, all resolved in real-time and real-space by liquid-phase TEM. A diversity of properties for differently shaped anisotropic nanoparticles are mapped, including the anisotropic interaction landscape of nanoprisms, curvature-dependent and staged etching profiles of nanorods, and an unexpected kinetic law of first-order chaining assembly of concave nanocubes. These systems representing properties at the nanoscale are otherwise experimentally inaccessible. Compared to the prevalent image segmentation methods, U-Net shows a superior capability to predict the position and shape boundary of nanoparticles from highly noisy and fluctuating background-a challenge common and sometimes inevitable in liquid-phase TEM videos. We expect our framework to push the potency of liquid-phase TEM to its full quantitative level and to shed insights, in high-throughput and statistically significant fashion, on the nanoscale dynamics of synthetic and biological nanomaterials.
View details for DOI 10.1021/acscentsci.0c00430
View details for PubMedID 32875083
View details for PubMedCentralID PMC7453571
Effects of Particle Size on Mg2+ Ion Intercalation into lambda-MnO2 Cathode Materials
2019; 19 (7): 4712–20
An emergent theme in mono- and multivalent ion batteries is to utilize nanoparticles (NPs) as electrode materials based on the phenomenological observations that their short ion diffusion length and large electrode-electrolyte interface can lead to improved ion insertion kinetics compared to their bulk counterparts. However, the understanding of how the NP size fundamentally relates to their electrochemical behaviors (e.g., charge storage mechanism, phase transition associated with ion insertion) is still primitive. Here, we employ spinel λ-MnO2 particles as a model cathode material, which have effective Mg2+ ion intercalation but with their size effect poorly understood to investigate their operating mechanism via a suite of electrochemical and structural characterizations. We prepare two differently sized samples, the small nanoscopic λ-MnO2 particles (81 ± 25 nm) and big micron-sized ones (814 ± 207 nm) via postsynthesis size-selection. Analysis of the charge storage mechanisms shows that the stored charge from Mg2+ ion intercalation dominates in both systems and is ∼10 times higher in small particles than that in the big ones. From both X-ray diffraction and atomic-resolution scanning transmission electron microscopy imaging, we reveal a fundamental difference in phase transition of the differently sized particles during Mg2+ ion intercalation: the small NPs undergo a solid-solution-like phase transition which minimizes lattice mismatch and energy penalty for accommodating new phases, whereas the big particles follow conventional multiphase transformation. We show that this pathway difference is related to the improved electrochemical performance (e.g., rate capability, cycling performance) of small particles over the big ones which provides important insights in encoding within the particle dimension, that is, the single-phase transition pathway in high-performance electrode materials for multivalent ion batteries.
View details for DOI 10.1021/acs.nanolett.9b01780
View details for Web of Science ID 000475533900064
View details for PubMedID 31251071
Hierarchical self-assembly of 3D lattices from polydisperse anisometric colloids
2019; 10: 1815
Colloids are mainly divided into two types defined by size. Micron-scale colloids are widely used as model systems to study phase transitions, while nanoparticles have physicochemical properties unique to their size. Here we study a promising yet underexplored third type: anisometric colloids, which integrate micrometer and nanometer dimensions into the same particle. We show that our prototypical system of anisometric silver plates with a high polydispersity assemble, unexpectedly, into an ordered, three-dimensional lattice. Real-time imaging and interaction modeling elucidate the crucial role of anisometry, which directs hierarchical assembly into secondary building blocks-columns-which are sufficiently monodisperse for further ordering. Ionic strength and plate tip morphology control the shape of the columns, and therefore the final lattice structures (hexagonal versus honeycomb). Our joint experiment-modeling study demonstrates potentials of encoding unconventional assembly in anisometric colloids, which can likely introduce properties and phase behaviors inaccessible to micron- or nanometer-scale colloids.
View details for DOI 10.1038/s41467-019-09787-6
View details for Web of Science ID 000464979600009
View details for PubMedID 31000717
View details for PubMedCentralID PMC6472373
- Reconfigurable nanoscale soft materials CURRENT OPINION IN SOLID STATE & MATERIALS SCIENCE 2019; 23 (1): 41–49
Liquid-phase TEM imaging of self-assembly pathways of anisotropic nanoparticles
Microscopy and Microanalysis
2019; 25 (S2): 1414-1415
View details for DOI 10.1017/S1431927619007803
Synthesis and Self-Assembly of Janus and Triblock Patchy Particles
Self-Assembly of Nano- and Micro-structured Materials using Colloidal Engineering
Elsevier . 2019: 61–85
View details for DOI 10.1016/B978-0-08-102302-0.00004-3
Colloidal Metal-Organic Framework Hexapods Prepared from Postsynthesis Etching with Enhanced Catalytic Activity and Rollable Packing
ACS APPLIED MATERIALS & INTERFACES
2018; 10 (48): 40990–95
Recent studies on the effect of particle shapes have led to extensive applications of anisotropic colloids as complex materials building blocks. Although much research has been devoted to colloids of convex polyhedral shapes, branched colloids remain largely underexplored because of limited synthesis strategies. Here we achieved the preparation of metal-organic framework (MOF) colloids in a hexapod shape, not directly from growth but from postsynthesis etching of truncated rhombic dodecahedron (TRD) parent particles. To understand the branch development, we used in situ optical microscopy to track the local surface curvature evolution of the colloids as well as facet-dependent etching rate. The hexapods show unique properties, such as improved catalytic activity in a model Knoevenagel reaction likely due to enhanced access to active sites, and the assembly into open structures which can be easily integrated with a self-rolled-up nanomembrane structure. Both the postsynthesis etching and the hexapod colloids demonstrated here show a new route of engineering micrometer-sized building blocks with exotic shapes and intrinsic functionalities originated from the molecular structure of materials.
View details for DOI 10.1021/acsami.8b17477
View details for Web of Science ID 000452694100005
View details for PubMedID 30398328
Reconfigurable Polymer Shells on Shape-Anisotropic Gold Nanoparticle Cores
MACROMOLECULAR RAPID COMMUNICATIONS
2018; 39 (14): e1800101
Reconfigurable hybrid nanoparticles made by decorating flexible polymer shells on rigid inorganic nanoparticle cores can provide a unique means to build stimuli-responsive functional materials. The polymer shell reconfiguration has been expected to depend on the local core shape details, but limited systematic investigations have been undertaken. Here, two literature methods are adapted to coat either thiol-terminated polystyrene (PS) or polystyrene-poly(acrylic acid) (PS-b-PAA) shells onto a series of anisotropic gold nanoparticles of shapes not studied previously, including octahedron, concave cube, and bipyramid. These core shapes are complex, rendering shell contours with nanoscale details (e.g., local surface curvature, shell thickness) that are imaged and analyzed quantitatively using the authors' customized analysis codes. It is found that the hybrid nanoparticles based on the chosen core shapes, when coated with the above two polymer shells, exhibit distinct shell segregations upon a variation in solvent polarity or temperature. It is demonstrated for the PS-b-PAA-coated hybrid nanoparticles, the shell segregation is maintained even after a further decoration of the shell periphery with gold seeds; these seeds can potentially facilitate subsequent deposition of other nanostructures to enrich structural and functional diversity. These synthesis, imaging, and analysis methods for the hybrid nanoparticles of anisotropically shaped cores can potentially aid in their predictive design for materials reconfigurable from the bottom up.
View details for DOI 10.1002/marc.201800101
View details for Web of Science ID 000439816900022
View details for PubMedID 29722094
Imaging the polymerization of multivalent nanoparticles in solution
2017; 8: 761
Numerous mechanisms have been studied for chemical reactions to provide quantitative predictions on how atoms spatially arrange into molecules. In nanoscale colloidal systems, however, less is known about the physical rules governing their spatial organization, i.e., self-assembly, into functional materials. Here, we monitor real-time self-assembly dynamics at the single nanoparticle level, which reveal marked similarities to foundational principles of polymerization. Specifically, using the prototypical system of gold triangular nanoprisms, we show that colloidal self-assembly is analogous to polymerization in three aspects: ensemble growth statistics following models for step-growth polymerization, with nanoparticles as linkable "monomers"; bond angles determined by directional internanoparticle interactions; and product topology determined by the valency of monomeric units. Liquid-phase transmission electron microscopy imaging and theoretical modeling elucidate the nanometer-scale mechanisms for these polymer-like phenomena in nanoparticle systems. The results establish a quantitative conceptual framework for self-assembly dynamics that can aid in designing future nanoparticle-based materials.Few models exist that describe the spontaneous organization of colloids into materials. Here, the authors combine liquid-phase TEM and single particle tracking to observe the dynamics of gold nanoprisms, finding that nanoscale self-assembly can be understood within the framework of atomic polymerization.
View details for DOI 10.1038/s41467-017-00857-1
View details for Web of Science ID 000412053100007
View details for PubMedID 28970557
View details for PubMedCentralID PMC5624893
Polymerization-Like Co-Assembly of Silver Nanoplates and Patchy Spheres
2017; 11 (8): 7626–33
Highly anisometric nanoparticles have distinctive mechanical, electrical, and thermal properties and are therefore appealing candidates for use as self-assembly building blocks. Here, we demonstrate that ultra-anisometric nanoplates, which have a nanoscale thickness but a micrometer-scale edge length, offer many material design capabilities. In particular, we show that these nanoplates "copolymerize" in a predictable way with patchy spheres (Janus and triblock particles) into one- and two-dimensional structures with tunable architectural properties. We find that, on the pathway to these structures, nanoplates assemble into chains following the kinetics of molecular step-growth polymerization. In the same mechanistic framework, patchy spheres control the size distribution and morphology of assembled structures, by behaving as monofunctional chain stoppers or multifunctional branch points during nanoplate polymerization. In addition, both the lattice constant and the stiffness of the nanoplate assemblies can be manipulated after assembly. We see highly anisometric nanoplates as one representative of a broader class of dual length-scale nanoparticles, with the potential to enrich the library of structures and properties available to the nanoparticle self-assembly toolbox.
View details for DOI 10.1021/acsnano.7b02059
View details for Web of Science ID 000408520900009
View details for PubMedID 28715193
Quantifying the Self-Assembly Behavior of Anisotropic Nanoparticles Using Liquid-Phase Transmission Electron Microscopy
ACCOUNTS OF CHEMICAL RESEARCH
2017; 50 (5): 1125–33
For decades, one of the overarching objectives of self-assembly science has been to define the rules necessary to build functional, artificial materials with rich and adaptive phase behavior from the bottom-up. To this end, the computational and experimental efforts of chemists, physicists, materials scientists, and biologists alike have built a body of knowledge that spans both disciplines and length scales. Indeed, today control of self-assembly is extending even to supramolecular and molecular levels, where crystal engineering and design of porous materials are becoming exciting areas of exploration. Nevertheless, at least at the nanoscale, there are many stones yet to be turned. While recent breakthroughs in nanoparticle (NP) synthesis have amassed a vast library of nanoscale building blocks, NP-NP interactions in situ remain poorly quantified, in large part due to technical and theoretical impediments. While increasingly many applications for self-assembled architectures are being demonstrated, it remains difficult to predict-and therefore engineer-the pathways by which these structures form. Here, we describe how investigations using liquid-phase transmission electron microscopy (TEM) have begun to play a role in pursuing some of these long-standing questions of fundamental and far-reaching interest. Liquid-phase TEM is unique in its ability to resolve the motions and trajectories of single NPs in solution, making it a powerful tool for studying the dynamics of NP self-assembly. Since 2012, liquid-phase TEM has been used to investigate the self-assembly behavior of a variety of simple, metallic NPs. In this Account, however, we focus on our work with anisotropic NPs, which we show to have very different self-assembly behavior, and especially on how analysis methods we and others in the field are developing can be used to convert their motions and trajectories revealed by liquid-phase TEM into quantitative understanding of underlying interactions and dynamics. In general, liquid-phase TEM studies may help bridge enduring gaps in the understanding and control of self-assembly at the nanoscale. For one, quantification of NP-NP interactions and self-assembly dynamics will inform both computational and statistical mechanical models used to describe nanoscale phenomena. Such understanding will also lay the groundwork for establishing new and generalizable thermodynamic and kinetic design rules for NP self-assembly. Synergies with NP synthesis will enable investigations of building blocks with novel, perhaps even evolving or active behavior. Moreover, in the long run, we foresee the possibility of applying the guidelines and models of fundamental nanoscale interactions which are uncovered under liquid-phase TEM to biological and biomimetic systems at similar dimensions.
View details for DOI 10.1021/acs.accounts.7b00048
View details for Web of Science ID 000401674600001
View details for PubMedID 28443654
In Situ Electron Microscopy Imaging and Quantitative Structural Modulation of Nanoparticle Superlattices
2016; 10 (11): 9801–8
We use liquid-phase transmission electron microscopy (LP-TEM) to characterize the structure and dynamics of a solution-phase superlattice assembled from gold nanoprisms at the single particle level. The lamellar structure of the superlattice, determined by a balance of interprism interactions, is maintained and resolved under low-dose imaging conditions typically reserved for biomolecular imaging. In this dose range, we capture dynamic structural changes in the superlattice in real time, where contraction and smaller steady-state lattice constants are observed at higher electron dose rates. Quantitative analysis of the contraction mechanism based on a combination of direct LP-TEM imaging, ensemble small-angle X-ray scattering, and theoretical modeling allows us to elucidate: (1) the superlattice contraction in LP-TEM results from the screening of electrostatic repulsion due to as much as a 6-fold increase in the effective ionic strength in the solution upon electron beam illumination; and (2) the lattice constant serves as a means to understand the mechanism of the in situ interaction modulation and precisely calibrate electron dose rates with the effective ionic strength of the system. These results demonstrate that low-dose LP-TEM is a powerful tool for obtaining structural and kinetic properties of nanoassemblies in liquid conditions that closely resemble real experiments. We anticipate that this technique will be especially advantageous for those structures with heterogeneity or disorder that cannot be easily probed by ensemble methods and will provide important insight that will aid in the rational design of sophisticated reconfigurable nanomaterials.
View details for DOI 10.1021/acsnano.6b05270
View details for Web of Science ID 000388913100007
View details for PubMedID 27723304