I probably should have posted this earlier, but if you are in downtown fargo tomorrow with nothing to do...

Weekend Fun

The fuel pump went on my truck last week (a 1998 F150 4.6L V8).  So I had to drop the tank and install a new pump.  The pump failed because it relies on rubber components in order to maintain pressure in the fuel lines.  This might sound surprising; the pump in this vehicle is located inside the gas tank where we might expect it to be relatively protected.  The failure here falls under the mysterious category of ‘ageing’.  It is not always clear what happens to the elastomer exposed to gasoline, but the result is clear.  The stress eventually leads to fracture, and failure of the component.  Add it to the list of other good problems in polymer science!

Aspiration of a Block Copolymer Emulsion Droplet

In this movie we see an oil droplet (in water) that is loaded with a surfactant being drawn into a thin micropipette.  In particular we use poly ethylene oxide - b - poly styrene as a surfactant, and toluene as the oil.  As the drop is drawn into the pipette, its surface area changes and with a measurement of the pressure applied by the pipette a force - surface area curve can be constructed.  Remember your first year physics - a force vs distance graph will get you a spring constant!  In other words, we are measuring the surface modulus of the droplet.  We hope that fooling around with the surfactant molecule concentration etc. will lead us to a better understanding of the molecular details of the interface.

Buckled Particle Films

Here are two Laser Scanning Confocal Microscope images of a buckled monolayer of polystyrene particles. What should be clear is that there is a repeating pattern to the buckles (a wavelength). This is in remarkable contrast to what is expected - conventional elastic instabilities of this sort (known as wrinkles) require a bending modulus in the film. A traditional bending modulus cannot occur in the particle film, as the particles are free to rotate. The physics is about the 'torque chain', the way each sphere's rotation is matched by its neighbours. We are working on a very simple model, but are struggling with the difference between a well ordered hexagonally packed crystal of monodisperse spheres, and the disorder in the polydisperse sample.

Polydisperse Spheres