Download PDF (9.49MB) - the School of Engineering and Applied ...
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WWW.SEAS.UPENN.EDU The Lee Research Group has developed a unique method to control the flow of multiphasic fluids to generate emulsions and bubbles. Shown above is the production of highly monodisperse double emulsions using a capillary microfluidic device. works, he doesn’t want to just make something work,” Tettey says. “That changed my perception of how I should approach science, and made me try to figure out the fundamental behavior of what I observe. As a scientist, that’s a very important curiosity to have, because it gives you better control of the end product.” “God Particles” to the Rescue To better control the end product in another research project, Lee has turned to a special type of particle named after the Roman god of beginnings, transitions and endings. Similar to its namesake, a Janus particle has “two faces,” that is, two surfaces with distinct physical properties. For instance, one half of its surface may be hydrophilic, while the other half is hydrophobic. At fluid-fluid interfaces, such as those that form in mixtures containing oil and water, the water-loving region of a Janus particle spontaneously faces the water side of the interface, while the water-hating region orients itself toward the oil side. Because of their unique two-faced property and strong attraction to fluid-fluid interfaces, Lee believes that Janus particles are ideal for producing thermodynamically stable mixtures consisting of different fluids that stay evenly dispersed rather than separating into distinct layers. By understanding and ultimately controlling the behavior of Janus particles at fluid-fluid interfaces, he hopes to optimize the properties of a range of soft materials, from vaccines and mixture-based medicines to detergents and microreactors for biofuel conversion. To study Janus particles, Lee often first develops numerical models to predict their behavior at SPRING 2013 n 8
fluid-fluid interfaces, and then observes their behavior under the microscope to confirm these predictions and generate new information to further develop the theories. “The biggest challenge is that we cannot see everything that’s happening, so it’s very difficult to come up with the exact mechanism to describe what’s leading to the macroscopic properties or phenomena that we observe,” Lee says. “That’s why we need to have this crosstalk between modeling and experiments.” Lee has discovered that by tweaking the shape of Janus particles, morphing them from spheres to snowmanlike particles, and then modifying the relative size of the snowman’s hydrophilic head compared with its hydrophobic body, he can control their orientation, behavior and interactions at fluid-fluid interfaces. Lee’s calculations for guiding the synthesis of non-spherical Janus particles can be used to stabilize fluid mixtures, thereby extending the shelf life of food, medicine and personal hygiene products, and also enabling enhanced oil recovery from oil fields. Synergistic Impact Lee grew up in South Korea and earned his bachelor’s degree in chemical engineering at Seoul National University in 2001. Encouraged by his undergraduate advisor to become a scientist, Lee decided to come to the United States for the best opportunities to pursue his dream. While earning his doctoral degree in chemical engineering at the Massachusetts Institute of Technology, he initially focused on polymers and then started to apply techniques in polymer science to soft nanomaterials. PENN ENGINEERING n 9
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fluid-fluid interfaces, <strong>and</strong> <strong>the</strong>n observes <strong>the</strong>ir behavior<br />
under <strong>the</strong> microscope to confirm <strong>the</strong>se predictions<br />
<strong>and</strong> generate new information to fur<strong>the</strong>r develop <strong>the</strong><br />
<strong>the</strong>ories. “The biggest challenge is that we cannot see<br />
everything that’s happening, so it’s very difficult to<br />
come up with <strong>the</strong> exact mechanism to describe what’s<br />
leading to <strong>the</strong> macroscopic properties or phenomena<br />
that we observe,” Lee says. “That’s why we need to have<br />
this crosstalk between modeling <strong>and</strong> experiments.”<br />
Lee has discovered that by tweaking <strong>the</strong> shape <strong>of</strong> Janus<br />
particles, morphing <strong>the</strong>m from spheres to snowmanlike<br />
particles, <strong>and</strong> <strong>the</strong>n modifying <strong>the</strong> relative size <strong>of</strong><br />
<strong>the</strong> snowman’s hydrophilic head compared with its<br />
hydrophobic body, he can control <strong>the</strong>ir orientation,<br />
behavior <strong>and</strong> interactions at fluid-fluid interfaces. Lee’s<br />
calculations for guiding <strong>the</strong> syn<strong>the</strong>sis <strong>of</strong> non-spherical<br />
Janus particles can be used to stabilize fluid mixtures,<br />
<strong>the</strong>reby extending <strong>the</strong> shelf life <strong>of</strong> food, medicine <strong>and</strong><br />
personal hygiene products, <strong>and</strong> also enabling enhanced<br />
oil recovery from oil fields.<br />
Synergistic Impact<br />
Lee grew up in South Korea <strong>and</strong> earned his bachelor’s<br />
degree in chemical engineering at Seoul National<br />
University in 2001. Encouraged by his undergraduate<br />
advisor to become a scientist, Lee decided to come to<br />
<strong>the</strong> United States for <strong>the</strong> best opportunities to pursue<br />
his dream. While earning his doctoral degree in<br />
chemical engineering at <strong>the</strong> Massachusetts Institute<br />
<strong>of</strong> Technology, he initially focused on polymers <strong>and</strong><br />
<strong>the</strong>n started to apply techniques in polymer science<br />
to s<strong>of</strong>t nanomaterials.<br />
PENN ENGINEERING n 9
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