Emulsions Near the Glass Transition

Ted Brzinski, Dandan Chen, Joaquim Clara-Rahola, Cortney Crane, Ken Desmond, Laura (Golick) Gray, Charlotte Hollinger, Xia Hong, Raul Gonzalez, Meghan Kohne, Dave Schaar, Pearl Young, and Eric Weeks

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Our research aims to reveal how liquid colloid systems can exhibit granular characteristics. Though liquid at the microscopic level, emulsions such as mayonnaise and shaving-cream, can form mesoscopic structures that pile like sand. Furthermore, near the 'glass transition' these may demonstrate interesting granular and/or nongranular properties.

Like mayonnaise or soap, our investigation media is an emulsion, composed of tiny droplets of organic solvent suspended in an aqueous phase. When tightly packed, the droplets become deformed, moving closer to one another than is possible for the solid colloidal spheres researched extensively in our lab. This capacity for compression may contribute to interesting phenomena. We plan to observe the compression of droplets as the concentration approaches that of a jammed system.

The following 2D and 3D images were taken with a Confocal Microscope. They display Dodecane droplets in a continuous phase of water/glycerol mixture. A fluorescent dye was added to the continuous phase in order to facilitate microscopy, and the colours have been enhanced to emphasize the continuous/droplet interface. The droplets are different sizes. Compression of packed droplets is visible.

(Click on any image to view its enlargement).

Additional Information Regarding Emulsions

Emulsions are not remote from common experience. Two of the most prevalent emulsion systems are mayonnaise and soap. In both systems, substances which normally separate from one another are made able to mix by the addition of an emulsifyer (surfactant/surface acting agent). This mediating ingredient is unique because it is able to associate with both substances and stabilize their interaction. Thus, instead of forming phases (like an oil layer on water), small droplets of one substance are able to persist, suspended in the other.

The emulsions we create are oil in water emulsions in which the continuous phase is an aqueous mixture of water and glycerol and the droplet phase consists of an organic solvent such as Dodecane. The glycerol is necessary for index-matching purposes in order to achieve clear 3D confocal images. Our surfactant (SDS) is an amphipathic molecule composed of a hydrophilic head (which associates with the continuous phase) and a hydrophobic tail (which interacts with the droplet phase). The following diagram displays an idealized image of an emulsion droplet:

(Click on the thumbnail to view an enlargement).

For more on mayonnaise and soap emulsions, please refer to these websites:

For more information, please contact Eric Weeks: weeks(at)physics.emory.edu