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