Fluid Flows: From Singularities to Microscales
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Prof. Nagel's group studies the phenomenon of viscous withdrawal
. The group has studied the effect of viscosity and geometry on the thin-ness of the withdrawn fluid thread or spout. Now they are looking into transient motions that occur when the fluid is perturbed. One effect is a transient disappearance of the thread, followed by its reappearance. A second current topic is the effect of non-newtonian polymeric liquids on the thread-forming phenomenon. Meanwhile the applied work of using this phenomenon to encapsulate and protect clusters of cells for treatment of disease is continuing. There may be some aspect of this development that would make a good student project. Some experience with chemistry experiments would be valuble.
Nagel's group studies the way liquids splash against a surface. They discovered that if part of the air is removed the liquid spreads along the surface and does not splash. Now they are studying the quantitative relation betwen air density and splash formation. They are using fast video cameras to observe the initial stages of the splashing instability.
Two experimental groups study fluid membranes that form spontaneously when lipid molecules mix with water. Nagel's group studies a threadlike structure called a myelin caused by the expansion of lipid multilayers into water. The mechanical properties and motions of these structures are a topic of current study. Lipid monolayers in a Langmuir trough and lipid bilayer vesicles are under active study in Ka Yee Lee's group. Here there is a continuing program to understand the spontaneous growth of pancake, tube, star and paisley structures in compressed monolayers.
A further form of fluid deformation occurs in the microfluidic channels. Streams of immiscible fluid injected into a chanel break off and form droplets whose internal motion can be finely controlled. Current research is about the effect of the shape of the channel and ways to control the interaction of pairs of drops.
Our most recent progress report on this area (known as an IRG) for the National Science Foundation appears here
Self-organized periodic nanostructures on surfaces
Prof. Jaeger's group makes two-dimensional nanocrystal arrays by a kinetic process in which rapid kinetics promotes ordering. [Kinetically-Driven Self Assembly of Highly-Ordered Nanoparticle Monolayers
Terry P. Bigioni*, Xiao-Min Lin , Toan T. Nguyen*, Eric I. Corwin*+, Thomas A. Witten*+, and Heinrich M. Jaeger*+. Nature Materials, submitted]
Prof. Sibener's group specializes in polymer films the spontaneously phase separate to form regular, periodic stripes. Prof. Jaeger's group has developed ways to improve the ordering of the stripes and also to make deposited metals follow these stripes. See Microdomain polymer films for further information.Jammed granular flow
[Granular jets
S. T. Thoroddsen and Amy Q. Shen
PHYSICS OF FLUIDS VOLUME 13, p. 4 NUMBER 1 JANUARY 2001] The recent study of granular jets in Prof. Jaeger's group revealed unexpected structure, via time-resolved x-rays. A separate study shows a geometry of sheared granular flow where the motion is not confined to a narrow boundary layer, but instead spreads to a macroscopic region. See item 3
For a bit more information look here..
Jammed electron spins in magnets
Jammed colloidal particles
Prof. Rice's group has discovered surprises in the brownian motion in collections of micron-sized colloidal spheres. The motion is heterogeneous and correlated (Cooperative dynamics in two-dimensions. Phys. Rev. Lett., 92, 035502 (2004).). For a bit more detail see the last paragraph here.
Stochastic Cell motions
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The Cluzel group studies the random motions of primitive e-coli cells as they swim in a liquid medium in search of nutrients or to avoid poisons. This news story explains some of the experimental methods used, as well as some of the simulation methods used to account for the observed motions mechanistically.
Look here under "Cluzel".
Responsive biogel
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A gel whose molecular links are made of protein can expand or contract in response to the presence of small molecules that selectively bind to specific sites on the protein. Look here under Profs. Kron and Mrksich, who developed this gel.
Quantum Dot arrays
The picture shows an array of gold particles 5 nm in diameter. Such tiny particles are called quantum dots, because the the size is small enough to affect the quantum wave properties of the electrons. The Jaeger group measures the way these arrays conduct electrical current, as told here. The relationship between current and voltage is nonlinear, and the nonlinearity shows that the array is electrically much different than a continuous layer of metal. Current studies by Prof. Kang investigate magnetic dot particles such as nickel. Then the electric current depends greatly on the applied magnetic field. Prof. Guyot-Sionnest investigates the behavior of dots made of semiconductors. These emit bright fluorescent light with a mysterions temporal structure. A solid film of these dots can have voltage-controlled fluorescence, as Prof. Guyot-Sionnest's papers show.