If you want to understand how molecules interact, there's nothing quite like crawling around inside them, and perhaps moving an atom by hand to see what's happening behind it.
Chemists and computer scientists are using a special facility at NIST to do just that. By standing in front of two floor-to-ceiling display screens and donning special eyewear they can immerse themselves in a 3D environment constructed using data from theoretical studies. The facility uses software developed by NIST to represent large, complex sets of data, enabling researchers to answer questions that might otherwise defy attempts at solution. The scientists are thus face to face with giant-sized molecules whose behavior can be seen and understood in minutes instead of the weeks required using traditional techniques.
NIST scientists and collaborators are using this capability to study "smart gels," which might someday be used to make exotic foods, cosmetics, medicines, sensors, and other technological gizmos. Smart gels are inexpensive materials that expand or contract in response to external stimuli. This property could be useful in applications such as an artificial pancreas that releases insulin inside the body in response to high sugar levels. But scientists need to understand how the molecules in these materials behave before they can easily create the best "recipes" for each product.
The NIST team is studying a subclass of these materials called "shake gels." Through some complex and as yet unknown process, these watery mixtures of clays and polymers firm up into gels when shaken, and then relax again to the liquid phase after some time has passed. A shake gel might be used, for example, in shock absorbers for cars. The material would generally be a liquid but would form a gel when the car drove over a pothole; the gel thickness would adjust automatically to the weight of the car and the size of the pothole. A more esoteric application might be the formation of gelled areas within a liquid where holograms could be created using a laser.
The 3-D visualization facility helped the scientists see that it is the polymer's oxygen atoms, instead of the hydrogen atoms as previously thought, that attach to the clay. The team has also made theoretical calculations that may help to explain why and how the components of the liquid mixture bind together into a semisolid form. Electrical charges affect the binding process, resulting in water binding to clay surfaces in a perpendicular arrangement, which is believed to help create the firmness of the gel. This work is described in a forthcoming paper in the Journal of Physical Chemistry B. The work is sponsored by Kraft Foods and involves scientists from NIST, Los Alamos National Laboratory, and Harvard University.
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