Behavior of a Droplet with a Reactive Interface Angela M Jiménez2, Sigolene Lecuyer1, Howard Stone1, Andrew Belmonte3

1Harvard University School of Engineering & Applied Sciences, 2The City College of New York, 3The Pennsylvania State University

DMR 0649199

The interaction between anionic and cationic surfactants leads to the formation of a visco-elastic material at the interface between a cetyl trimethylammonium bromide (CTAB) solution and oleic acid. When the reaction occurs on the surface of a sedimenting droplet, this results in unusual behavior and shape transformations, which we study as a function of CTAB concentration and size of the drop.

Oleic Acid

CTAB solution

7l drop of 20 mM CTAB solution

sedimenting in oleic acid

Buried in the 2D hologram at right is all of the information necessary to reconstruct particle locations in a 3D sample—in this case, beads embedded in a polyacrilamide gel with a cell (the bright oblong patch) plated on top. This ability to capture 3D information in every frame gives holographic microscopy the potential to yield insights into 3D dynamics on short timescales. Our goal is to observe the beads moving in the gel—both with and without external driving forces—to discover more about the material properties of the cell directly above. Hologram of Cell on

Polyacrilamide Gel

Investigating Cell Mechanics with Digital Holographic Microscopy

Elizabeth Jerison2, Tommy Angelini1, Ryan McGorty1, David Weitz1, Vinothan Manoharan1

1Harvard School of Engineering and Applied Sciences, 2Yale University

DMR 0649199

Scanning Electron Images of (left) square PDMS micro-channel and (right) glass coated channel

PDMS micro-fluidic channels swell or dissolve in the presence of many common organic solvents, which greatly limits their chemical compatibility and usefulness. We solve this problem by coating the channels with a glass layer using sol-gel chemistry. This glass layer is impermeable to chemicals and can be functionalized with a wide range of commercially available silanes to control the wet-ability of the micro-channels. In addition, the coating rounds off the sharp corners of rectangular micro-channels, making them ovular or even circular. This geometry simplifies the flow profiles in the channels and may be exploited to produce exceedingly mono-disperse emulsions.

Impermeable Coating for PDMS MicrochannelsThao Do2, Adam Abate1, David Weitz1

1Harvard School of Engineering & Applied Sciences2Virginia Polytechnic Institute and State University

DMR 0649199