Tuesday, November 26, 2013

Hey everyone! My name is Liana Vaccari and I’m a PhD student in Chemical Engineering at the University of Pennsylvania. The research group I’m a part of has spent a lot of time understanding how things change at fluid interfaces, especially with microscopic particles. I took that know-how to look at the behavior of the oil-seawater interface when it is covered with a natural microparticle: bacteria. In the ocean, there are some bacteria that know when even small amounts of oil are present and they can feed on it. Encouraging them to eat the oil is a great way to get rid of this pollutant, but it’s definitely not that simple. Some bacteria species also form strong biofilms on various surfaces, and I’m studying the evolution of a biofilm that the bacteria, Pseudomonas sp., make between the oil and seawater. This could affect the way drops get broken up in the water column (something David talked about in his post in October) if the biofilms surround it.

David talked about using the crude oil from the Gulf of Mexico. The reason it’s so nasty is that there are all sorts of molecules that change the properties of interfaces, etc. Therefore, I’ve been using a very simple oil to get a good starting point in understanding what happens just with bacteria present. My experiments are also on a much smaller scale than David’s. The needle in the image below is only 1 millimeter across. For perspective, a millimeter is approximately the thickness of a credit card.

This picture is of an oil drop and an oil layer that I aged in the bacteria suspension for a day. Afterwards, I pressed the drop against the layer above and deformed it significantly, but it didn’t pop! I was surprised at how strong it was,
and decided to learn more about the formation of the film.
Basically, I have been tracking how things (bacteria and very tiny beads) behave at the oil-water interface when I let it sit for a couple of days. My main tool for these experiments is a microscope, where I record a huge amount of data.


Soon, I’ll be integrating my work with some of the larger scale projects. This will give us a more realistic view of what is happening in the ocean when these oil spills happen.