Differential Dynamic Microscopy (DDM), Active: Xujun Zhang    Alumnus: Jinxin Fu

 DDM is a method pioneered by various groups, particularly that of Cerbino in Italy. We think of it as "dynamic light scattering where you want it". Like DLS, DDM tracks the motion of objects in solution. Instead of looking at the scattered light, though, one generates hundreds or even thousands of consecutive images. In most cases, the images themselves do not show anything! But when you subtract one from another, sequentially, differences appear. More and more differences with time. Fourier transformation of these differences results in information almost equivalent to what a DLS practitioner finds. What's the big deal? Well, with DDM you can zero in on just a section of a sample. For example, you might wish to know the motion of some particles trapped between grains of sand, or inside a leaf or capsule. Also, the information you get from DDM is obtained at very long distance scales. This makes the method somewhat less susceptible to polydispersity (at the shorter distance scaled probed by DLS, large objects cannot contribute their full strength to the scattering signal) but it makes DDM less adept at following rotational motion than DLS can be under appropriate circumstances. We are using DDM to track the motion of microbubbles. This situation is a veritable minefield to DLS, but DDM navigates it with ease. We are also exploring the limits of the method, which has not much of a track record compared to DLS, especially where synthetic polymers are concerned. 

Polypeptides,  Active: Alyssa Blake, Graham Parkinson  Alumni: Too many to list!


Our work with polypeptides began a long time ago! In those days, they were model rodlike systems for testing theories of liquid crystal formation and gelation. Work of a fundamental nature continues, especially on questions of dynamic behavior, but we are also concerned with ways to exploit polypeptides for production of useful materials. For example, Dr. Cornelia Rosu pioneered the use of rodlike polypeptides to "template" higher degrees of order in organic photoelectric materials (1). We are also pioneers in placing polypeptides on colloidal particles. The idea here is to merge all the wonderful features of polypeptides--chirality, ability to change their secondary conformation and dimensions, chemical versatility--with the easy manipulation conferred by particles. These polypeptide-particle composite materials form colloidal crystals, which hold the potential for manipulation of light in response to external stimulus.


  • Hydrophobins: Xujun Zhang, Drew Gorman   Alumni: Cornelia Rosu, Brian Khau

 Cellulose Nanocrystals: Bailey Risteen, Paul Balding, Graham Parkinson, Cornelia Rosu (Alumna)