DanAllan.com

Research

In one breath

I study the physics of soft interfacial materials, like layes of protein that build up when a bowl of milk is left out in the air. Interfaces like this are squishy in a complex way. To investigate that, I infuse them with microscopically small beads. By studying how these beads move through and around the squishy interface, I can characterize its mechanical properties.

In one elevator ride

I study the mechanical properties of protein layers, the gummy films that form when protein solutions, including foods like milk and raw egg, are exposed to air. As layers of protein form at the surface, they can be viscous like honey or elastic like rubber or a combination of both. Protein layers are thin and fragile, so measuring their viscosity or elasticity is tricky. I use microrhelogy, a technique developed in the 90′s by scientists at Exxon, Johns Hopkins, and elsewhere.

I float colloids — particles that are microscopic but still much larger than proteins — on a surface where a protein layer is forming. Left alone, the colloids perform Brownian motion, a random dance driven by atomic kicks. Or, under a magnet, magnetic colloids can be forced to travel or spin. I record the colloids through a microscope, and I track their trajectories using my own multiple particle tracking software. Knowing both their motion and the forces that drive them, whether thermal or magnetic, I can infer how the protein layer is impeding that motion, its drag.

From the drag exerted by the layer, it is possible to calculate its viscosity and elasticity (to be precise, its complex shear modulus). Doing this at the air–water interface in a protein layer complicates both the experiment and the theoretical machinery used to interpret the results. My thesis work is characterizing protein layers at the air–water and advancing the technique of interfacial microrheology.

I am studying under Robert L. Leheny in the Johns Hopkins Department of Physics and Astronomy.

In a journal article?

See the list of publications on my CV.

On GitHub

Nearly all of my code is online in a github repository. I have taken some pains to make it practical for others to use it; in fact it is now being used by several research groups. Installation is simple, and the code is neatly structured and documented. More collaborators are welcome!