Research Synopsis

We use nanoscale phenomena to create unique behavior and devices. Techniques such as Small Angle Neutron Scattering, Differential Scanning Calorimetry, Transmission Electron Microscopy, Scanning Electron Microscopy, Dynamic Light Scattering, Atomic Force Microscopy, Rheology, Pressure-Volume-Temperature measurements and Surface Tension measurements are all used to elucidate nano-phenomena. There are four main areas in which we concentrate our efforts: Thin polymer films, Confinement effects, Nanoparticle arrays and Molecular machines. These are briefly described below.

Thin polymer films - We have found that nanoparticles promote wetting contrary to expectation, particles usually act as nucleating sites for dewetting. Dewetting is an instability in thin (< 100 nm) polymer films that causes the film to form holes which grow in size, impinge with each other then break-up into small droplets when the polymer's surface energy is greater than the substrate's. We are investigating the fundamentals of why nanoparticles promote film stability and use this phenomenon to create stable films for surface acoustic wave sensors. In another project we are also developing a novel technique to write nanoscale information in thin films which are stabilized in another manner.

Confinement effects - Nanoparticles also produce confinement effects when blended with linear polymers. This link to our Nature Materials article explains the effect more fully. Basically, due to their very small size, nanoparticles can create very small gaps between themselves at low concentration. Since the particles are smaller than the polymer there does not seem to be a "depletion flocculation" effect and they are quite stable in solution. What we have found is that the viscosity decreases upon nanoparticle addition, a result at odds with Einstein's century old prediction that particles increase the viscosity of suspensions. One caveat, if the gap between the nanoparticles is bigger than the linear polymer then the viscosity increases. Only when the polymer is confined does the viscosity decrease. We are continuing the investigation of this effect and have found many interesting phenomena, more later...

Nanoparticle arrays - This project is part of a NIRT we have with Prof. Karen Wooley at Washington University - St. Louis. We are placing nanoparticles on surfaces in well defined arrays and deforming them to store a bit of information. This project builds on the IBM Millipede technology and stands to revolutionize data storage. Many nanoscale effects come into play and our aim is to understand them.

Molecular machines - A hybrid block copolymer is used to produce a molecular machine. This builds on our previous discovery that a hybrid linear-dendrimer block copolymer undergoes a phase transition when the relative size of either block is changed. We call this an entropically driven molecular machine and could be used as a sensor or drug delivery vehicle.

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