"I know nothing except the fact of my ignorance." ― Socrates

Ongoing Research Projects

Dynamics of Complex Colloidal Chains and Molecules (NASA, with Prof. Marr)

Biopolymers such as polynucleotides and polypeptides are ubiquitous in nature. Although they have relatively simple backbones, by virtue of site-specific interactions between rather limited sets of subunits along the chains, they can fold into proteins and DNA with well-defined 3D structures of exquisite complexity and functionality. In addition, biopolymers can also assemble into complex structures such as bundled microtubules, flagella, and cilia that undergo nonreciprocal motion in a viscous liquid, which drive processes essential for life ranging from nutrient transport to pathogen clearance to cell migration. Inspired by nature, we aim to fabricate and investigate the behavior of colloidal chains that closely resemble natural and synthetic macromolecules with tunable chain length, flexibility, composition, and architecture.


Functionalized Nanoparticles as New Gas Hydrate Anti-Agglomerates (ACS-PRF, with Prof. Sum)

Gas hydrates are inclusion compounds formed by the hydrogen-bonding of water to trap gas at elevated pressures and low temperatures. Their formation is a major concern in hydrocarbon production, as their agglomeration in flowlines can cause severe operational and economic losses. We investigate functionalized magnetic nanoparticles as a new class of anti-agglomerates. The advantages of these nanoparticles are that they can be functionalized to have the proper anti-agglomerate properties and conveniently recycled due to their strong magnetic response. This work brings the innovation in nanoscience to the field of gas hydrates to address a very practical and important problem in the petroleum industry.


Two-dimensional Colloidal Quasicrystals (NSF, with Prof. D.T. Wu)

A quasicrystal lacks translational symmetry but exhibits rotational order that is incompatible with conventional crystallographic order. Since its discovery in 1982, quasicrystals have revolutionized the paradigms concerning the order in crystallography and material science. Although atomic quasicrystals are predominantly intermetallic alloys, quasicrystalline structures have also been found in self-assembled soft materials, including metal-organic frameworks, nanoparticles, micelles, and polymers. The length scales of these building blocks, however, range from 0.5 nm to 50 nm, which are smaller than the diffraction limit of visible light. As a result, it is extremely challenging to observe their formation directly. We will investigate the assembly of colloidal microspheres into large-high-quality 2D quasicrystals (with equal lateral triangles and squares) by combining externally applied fields with geometric confinement. This will allow us to address fundamental questions in quasicrystal formation through optical characterization in both real space and real time.


Colloidal Microwheels Driven by Magnetic Fields (NSF, with Prof. Marr)

Colloidal assembly has been envisioned as an effective method for the bottom-up fabrication of micro- and nano-structures with a broad range of applications from sensors to photonics to biomedical devices. The utility of the approach arises from the ease with which interparticle interactions can be manipulated, providing an indirect method of controlling subsequent colloidal structure formation. However and while a variety of desired structures have been predicted, many are inaccessible because of thermodynamic or kinetic constraints on assembly or the challenge of separating them from a polydisperse mixture. Here, we overcome these limitations with applied rotating magnetic fields and superparamagnetic colloids, which form into wheel-like close-packed colloidal clusters well-suited for assembly into metamaterials. In addition, we have developed a surface-based translation strategy, inspired by the invention of the wheel, that overcomes the inherent reversibility of low Reynolds number flows by breaking symmetry using available surfaces.


Active Colloids as Microrobots under AC Electric Fields (NSF, with Prof. Donev)

Artificial motors that can carry payloads and deliver cargoes on demand could revolutionize many technologies ranging from targeted drug delivery to intelligent sensors. Here we investigate a new type of microrobots, the so-called electrohydrodynamic motors made from asymmetric particles and driven by AC electric fields. Since the flow fields surrounding individual particles can be manipulated in a much wider range than current model systems of active colloids, the electrohydrodynamic microrobots can be broadly applied by the scientific community to study challenging questions related to non-equilibrium physics. Although the electrode we use here is simple, it can be pixelated and fully integrated with MEMS devices. If successful, our research will provide the fundamental knowledge necessary for the development of technologies to manipulate micro- and nano-scale objects with both spatial and temporal regulations.