(6jp) Colloid and Nanoparticle Growth and Assembly Dynamics for Materials Design and Molecular Analogues

Research Interests: Colloids have the unparalleled ability to assemble into hierarchical structures and act as molecular analogues due to the multitude of possible particle-particle interactions, ranging from electrostatic to hydrodynamic forces. Approaches for assembling colloidal building blocks are often empirical in nature, especially for nanoscale colloids in which the assembly dynamics are not easily observed. Direct visualization of assembly dynamics for micron scale colloids leads to phenomenological understanding of the dominant physical mechanisms. In situ electron microscopy allows for similar real-time visualization of nanoscale systems in liquid, and promises to yield a depth of understanding to nanoparticle assembly as has been established in micron scale systems.

Successful Proposals: NRC Research Associateship Program Postdoctoral Fellowship

Postdoctoral Projects: “Imaging Biomimetic Magnetite Nanocrystals in Live Magnetotactic Bacteria and Protein Templates with Liquid Cell Electron Microscopy”

Under supervision of Tanya Prozorov, Division of Materials Science and Engineering, Ames Laboratory

“New Electron and Ion Transmission Techniques for Nanomaterial Characterization in and out of Liquid Environments”

Under supervision of Robert Keller, Advanced Chemicals and Materials Division, National Institute of Standards and Technology

Ph.D. Dissertation: “Direct Observations of Colloidal and Nanoparticle Behavior in the Presence of External Fields”

*Winner of 2014 Zuhair A. Munir award for best dissertation in the College of Engineering

Under the supervision of William D. Ristenpart and Nigel D. Browning at University of California, Davis, Department of Chemical Engineering and Materials Science

Research Experience: My research experience has been multidisciplinary but has always followed the common theme of applying chemical engineering principles to materials science problems. My formal Ph.D. training was in transport, fluid mechanics, and colloidal science, but through my joint adviser in Materials Science I was introduced to the field of in situ electron microscopy. Optical video microscopy experiments for observing and modelling electrokinetically induced micron scale colloidal assembly motivated me to apply similar approaches to nanoscale systems using in situ electron microscopy. Using this technique, I developed electron video microscopy techniques to observe colloidal nanoparticle growth, aggregation, and self-assembly, and modelled these observations using kinetic and scaling analyses inspired by my transport and fluid mechanics background. Through intensive training at several national laboratories, I have become proficient in several high resolution electron and ion microscopy techniques, which I continue to apply to reveal and explain hidden nanoscale transport processes.

Teaching Experience: During my undergraduate degree I was a peer-group tutor for engineering physics, a program that emphasized a Socratic method of teaching where tutors helped students answer problems by asking critical questions. In graduate school I TAed several laboratory courses, which involved teaching students experimental techniques, lecturing on course material, and critiquing lab reports and oral presentations. Additionally, I mentored several undergraduate researchers in graduate school as well as one graduate student during my postdoctoral studies. I plan to continue these teaching themes as a faculty member, for example using experimental demonstrations to visualize transport phenomena.

Future Direction: As faculty I plan to continue applying electron and optical video microscopy to different areas of nanoparticle and colloidal assembly. In particular I propose to apply in situ electron microscopy to an unsolved mystery I addressed during my Ph.D.: electric field induced aggregation of nanoparticles near electrodes. While many researchers suggest this occurs due to induced charge electrokinetic fluid flows, there are no direct observations of the aggregation dynamics.  In situ electron microscopy is an ideal technique for visualizing this phenomenon, which once understood could be exploited to form self-assembled superstructures with tunable order and material properties across many length scales. I plan to continue my work on electrokinetic manipulation of micron scale colloidal particles near electrodes, specifically developing new colloidal systems with analogous potential energy landscapes to atomic and molecular systems, such as superconductivity and surface sorption.

Besides assembly and growth of colloids and nanoparticles, my research interests include biomimetics and developing new electron and ion microscopy techniques with new contrast mechanisms.  In the future I foresee myself developing in situ electron microscopy techniques capable of imaging solvated ions in liquids, with applications for observing electric double layers and ion binding in biomimetic matrices. 

Selected Publications:

T.J. Woehl and T. Prozorov, The Mechanisms for Nanoparticle Surface Diffusion and Chain Self-Assembly Determined from Real-Time Nanoscale Kinetics in Liquid. J. Phys. Chem. C, 2015, 119, 21261-21269.

T.J. Woehl, B.J. Chen, K.L. Heatley, N.H. Talken, S.C. Bukosky, C.S. Dutcher, W.D. Ristenpart, Bifurcation in the equilibrium height of colloidal particles near an electrode in oscillatory electric fields: Evidence for a tertiary potential minimum. Phys. Rev. X, 2015, 5, 011023.

T.J. Woehl, S. Kashyap, E. Firlar, T. Perez-Gonzalez, D. Faivre, D. Trubitsyn, D.A. Bazylinski, T. Prozorov, Correlative Electron and Fluorescence Microscopy of Magnetotactic Bacteria in Liquid: Toward In Vivo Imaging. Sci. Rep., 2014, 4.

P. Abellan, T.J. Woehl, L.R. Parent, N.D. Browning, I. Arslan, Factors controlling quantitative liquid (scanning) transmission electron microscopy. Chem. Comm. 2014, 50, 4873-4880.

*Featured on the back cover

T.J. Woehl, C. Park, J.E. Evans, I. Arslan, W.D. Ristenpart, N.D. Browning, Direct Observation of Aggregative Nanoparticle Growth: Kinetic Modeling of the Size Distribution and Growth Rate. Nano Lett. 2013, 14, 373-378.

C.S. Dutcher†, T.J. Woehl†, N.H. Talken, W.D. Ristenpart, Hexatic-to-Disorder Transition in Colloidal Crystals Near Electrodes: Rapid Annealing of Polycrystalline Domains. Phys. Rev. Lett. 2013, 6, 128302.

†Equal author contribution

T.J. Woehl, J.E. Evans, I. Arslan, W.D. Ristenpart, N.D. Browning, Direct in situ determination of the mechanisms controlling nanoparticle nucleation and growth. ACS Nano 2012, 6, 8599-8610.

*Featured on weekly ACS Nano podcast

Book Chapters:

T.J. Woehl and T. Prozorov, Future prospects for biomolecular, biomimetic, and biomaterials research enabled by new liquid cell electron microscopy techniques. In Liquid Cell Electron Microscopy, edited by Frances Ross, 2015.