Summer 2012:  NYU  Center  For  Soft  Matter  Research

The main objective of soft matter research is to get a picture of what is going on at the atomic scale by watching particle interactions on the microscopic scale.  For this particular project, I worked with Ph.D. candidate Colm Kelleher in his studies on colloidal particle interactions on an oil-water interface.  I was tasked with making relatively flat oil-water interfaces and analyzing the diffusion characteristics of those particles using confocal microscopy.  The goal was to gain insight into his Ph.D. focus: the movement of colloidal particles in the potential well formed by a catenoid.

The flat oil water interfaces were created by first gluing a washer to a microscope slide.  A thin layer of oil was then pipetted on.   Water was then very carefully placed on top, taking care to ensure that the water did not slip under the oil.  The cover slip was then glued on and the sample was allowed to settle, with some particles going to the interface, and the majority settling at the bottom.  The sample was then placed in the confocal microscope, as shown in the schematic below.

The confocal microscope was then used to scan through the oil and water until the interface was found.  As can be seen in the video below, as the confocal scans through the water, it eventually reaches a layer of polystyrene particles at the interface.  It then enters the oil until it reaches a much denser layer of particles that have settled on the slide.

Once the oil-water interface was found, a video was taken of both the motion of the interface particles, and of the particles on the slide.  Since the particles on the slide do not move, their average motion was subtracted from the interface particle motion to account for any movement of the confocal microscope.  The particles were then tracked in Matlab, as can be seen below.

Lastly, diffusion characteristics of the particles were measured.  At the end of my time in the lab, those values were being compared to established constants.