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Topic Name: New class of "smart fluids" capable of switching from gel to liquid upon exposure to ultraviolet light
Category: Chemical
Research persons: Assistant Professor Srinivasa Raghavan & his team
Location: 1227C, Chem-Nuc Bldg. 090 ,University of Maryland ,College Park, MD 20742-2111, United States
Details
Members of the Department of Chemical and
Biomolecular Engineering's Complex Fluids and Nanomaterials Group, lead by
Assistant Professor Srinivasa Raghavan, have discovered a new class of "smart
fluids" capable of switching from gel to liquid upon exposure to ultraviolet
light. A paper detailing the group's findings, titled "A simple class of
photorheological fluids: Surfactant solutions with viscosity tunable by light,"
was recently published in the
Journal of the American Chemical Society (2007; 129(6) pp 1553 – 1559). The
paper was authored by graduate students Aimee M. Ketner and Rakesh Kumar,
alumnus Tanner S. Davies, undergraduate Patrick W. Elder, and professor Raghavan.
It is already generating interest in the scientific community, most recently
being discussed by Nature magazine’s materials@nature website,
Chemical Processing magazine, Materials Today, and
ScienceDaily.
Fluids capable of a state-change in response to
electric fields (electrorheological, ER), magnetic fields (magnetoreheological,
MR), and light (photorheological, PR) change instantly from liquids into
semi-solids or gels, then back again as the stimulus is applied or removed. ER-
and MR-based smart fluids are already in wide use in devices such as shock
absorbers for vehicles and buildings, valves and clutches, but their
light-triggered cousins have so far remained largely ignored by industry because
they are typically difficult and expensive to manufacture. The Raghavan group,
however, has engineered new kinds of PR fluids that can be created using
inexpensive chemicals found in most labs. The researchers believe that their
discovery could spur on the acceptance and use of PR fluids in commercial
applications, particularly in microscale devices such as microvalves or
microsensors, where light will be more effective than electrical or magnetic
fields for precision control.
The group’s smart fluids contain micelles,
strings of molecules that spontaneously form in water under the right
conditions. Initially, the micelles are long, wormlike chains that tend to get
entangled, much like a bowl of spaghetti, making the fluid thick and gel-like.
Upon exposure to UV radiation, the micelles’ length is drastically reduced due
to rearrangements of their constitutent molecules. The shortened micelles become
untangled, and the smart fluid becomes a thin, water-like liquid, with a
viscosity (thickness) that is reduced by 4 orders of magnitude (a factor of
10,000).
About researcher:
Assistant Professor
Dept. of Chemical &
Biomolecular Engineering
1227C, Chem-Nuc Bldg. 090
University of Maryland
College Park, MD 20742-2111
EDUCATION / EXPERIENCE
Postdoctoral Fellow,
Chemical Engineering Dept.,
University of Delaware, 1998-2001
Ph.D., Chemical Engineering,
North Carolina State University, Raleigh, 1998
B.Tech., Chemical Engineering, IIT Madras,
India, 1992
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Phone:
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(301) 405-8164
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Fax:
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(301) 405-0523
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Email:
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In picture:
1. Group members 2006 - click
to enlarge photo
2. Photo responsive (PR) fluids
consisting of CTAB and OMCA. When OMCA is in its trans from, its mixture with
CTAB gives rise to long, entangled wormlike micelles. Upon UV irradiation,
trans-OMCA gets photoisomerized to cis-OMCA, and the corresponding change in
molecular geometry causes a drastic reduction in micellar length.
3.
Funded:
The Complex Fluids and Nanomaterials Group’s
work on this project was funded by a seed grant from the
Small Smart Systems
Center (SSSC) at the University of Maryland and a CAREER award from the
NSF-CTS.
 
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