(Research) Four years in!

I’ve grown somewhat retrospective over the past month as this roughly coincides with the four year anniversary of moving our lab from Cleveland State University to Case Western Reserve University. As is the case with pretty much everyone, those four years presented many challenges that I could not have anticipated when I started back in January 2020. We’ve made significant accomplishments across the board in research, teaching, and service at CWRU in that time, but I felt compelled to take a look back at what our lab has accomplished in research and where we’re headed.

At the time of our move in late 2019, our main areas of research were in (1) the theoretical prediction of how an anisotropic particle interacts with a nearby solid boundary and (2) solid particles adsorbed to fluid-fluid interfaces. We had just begun to build the experimental tools to measure surface interactions of anisotropic particles, fabricate Janus particles, and probe the transient rheology and kinematics of a drying film. Since our move, we’ve invested heavily in strengthening our toolset in microscopy, but also expanded into rheology, microfluidics, and new imaging modalities, including Optical Coherence Tomography (OCT). I included below some snippets of our progress in that time and path forward, but please reach out if you want to learn more!

1) Dynamics of complex colloids near a boundary: This is our most ‘mature’ line of research in the lab. The goal with our work here is in the probing, via experiments, simulation, and theory, of how nano- to micrometer scale chemically or geometrically ‘anisotropic’ particles interact with a solid boundary. As we approached 2020, we had published a number of papers focused on predicting this interaction for a Janus (‘chemically anisotropic’) particle near a boundary (for example), but since then we’ve made significant experimental progress in two related areas.

First, we've started to understand how non-specific and specific interactions, mediated by polymers and designer peptides (with Julie Renner ) in the continuous phase, can modulate the speed of a catalytically active Janus particle. This work is really exciting because it suggests another non-invasive route for control of these active systems. Second, we're developing our understanding of how an anisotropic particle interacts with an evanescent field to scatter light. The hypothesis driving this work is the light scattered from a particle is a highly resolved reporter in both space and time of the particle’s position and orientation very near a boundary. This work aims to extend an experiment called Total Internal Reflection Microscopy (TIRM) from isotropic to anisotropic particles. We're calling this technique Scattering Morphology Resolved (SMR) TIRM because it uses the morphology of scattered light, rather than the integrated intensity, as the reporter signal. We found via both experiment and simulation the morphology is a good reporter of both orientation and separation distance. More recently, we updated the experimental apparatus to dramatically improve the quality of data we use to establish the orientational dependence of scattering (see Fig. 1). We're now near reporting the first measurement of a potential energy landscape for a geometrically anisotropic particle. We’re also dabbling in soft and deformable particles, motivated by some experiments we did with SMR-TIRM to infer the adhesion state of a red blood cell with a boundary (with Umut A. Gurkan and Michael Hinczewski).

2) Watching Paint Dry: For this project, we’re interested in understanding how the kinematics and rheology change in a complex fluid as solvent evaporates. This problem has a significant impact in a variety of industries, but our original target area was to focus on automobile coatings motivated by our corporate partner PPG工业公司 . It turns out that a significant portion of energy consumption during the assembly of an automobile is in the paint shop while the coating is being manufactured. Defects and other issues with the manufacturing process will tend to exacerbate that energy use, so our goal is to both better understand how these defects arise and to catch them during the manufacturing process. Our approach (with James Gilchrist ) has been to develop non-invasive tools to probe these phenomena based primarily on imaging via bright field microscopy, epifluorescence, confocal microscopy, and now OCT. Our first publication in this area introduced Variable Angle Inspection Microscopy (VAIM), which is used to measure the flow field of a transparent or translucent film as it sags at a user defined angle. This first publication focused on non-evaporating viscous fluids for benchmarking, but we’re close to releasing another paper using the VAIM on model paint systems undergoing solvent evaporation. An exciting new development in our lab has been the use of OCT to probe opaque non-equilibrium systems (see Fig. 2). We’re beginning to develop OCT as a non-invasive tool for tracking skinning in opaque films, which could be really exciting when paired with other techniques for developing a deeper physicochemical understanding of how and why a paint skins.

3) Energy, Manufacturing, and Sustainability: The final (extremely broad!) area that has developed since our move is that of energy systems and sustainable manufacturing, specifically how formulation choices impact performance, processing, and sustainability. One path of our work in this area is in the formulation design of energy storage systems, such as formulating slurry for a hybrid redox flow battery or in increasing the suspension density of active material in an electrode, both challenges deeply rooted in how formulation impacts performance and processing. Another path is more broadly centered on the sustainable manufacture of chemical products. We started to get interested in manufacturing before our move to CWRU as there were questions arising from our burgeoning paint project about how to deploy imaging techniques in a coating manufacturing environment. I began to learn then and now continually realize how many issues central to the manufacturing of chemical products (such as films, coatings, and packaging) are driven by sustainability. In some ways these questions are the ones that we as a community have always sought to answer. Namely, if I add/replace/remove ‘additive A’, what happens to our ability to manufacture that product and the ultimate function? Students are always surprised when I tell them the number of ingredients in a typical product - such as paint - usually a dozen or more! Now, companies are more often faced with the add/replace/remove question driven by sustainability. There are some really exciting things happening broadly at CWRU in this area and I’m currently planning a sabbatical focused on this specific topic, so I hope over the coming months and years to share those pieces of news!