Recipe for a 'shake gel'

© R. Rathe Full size image available through contact

Chemists and computer scientists are using a special facility at the National Institute of Standards and Technology (NIST) to scale molecules up for people-sized interactions. Using chemical data, NIST software, special eyewear, and floor-to-ceiling display screens, they create giant three-dimensional molecules that move. Molecular behavior can be seen and understood in minutes instead of the weeks required using traditional techniques.

NIST scientists and collaborators used the 3D facility to study "smart gels," inexpensive materials that expand or contract in response to external stimuli. For example, a "smart" artificial pancreas might release insulin inside the body in response to high sugar levels. Other applications may include exotic foods, cosmetics or sensors. But scientists need to better understand the molecular behavior of the gels before they can optimize them for specific products.

The NIST team is studying a category of these materials called shake gels. Mixtures of clays and polymers, these materials firm up into gels when shaken, and then gradually relax again to liquids. In a shock absorber, for instance, such materials would generally be liquid but would stiffen into a gel when the car drove over bumps or potholes.

The visualization facility helped the scientists see that it is the polymer's oxygen atoms, not the hydrogen atoms as previously thought, that attach to the clay. The team's theoretical calculations also showed that water binds to the clay surfaces in a perpendicular arrangement. This may help create the firmness of the gel. Described in the Aug. 28 issue of Journal of Physical Chemistry B, the work is sponsored by Kraft Foods and involves scientists from NIST, Los Alamos National Laboratory and Harvard University.