Researchers at the University of Maryland have developed what they call a simple, relatively inexpensive class of fluids that undergoes significant changes in viscosity when subjected to light. The viscosity of fluids composed of a cationic surfactant, cetyl trimethylammonium bromide, and a photosensitive organic acid or salt can drop more than four orders of magnitude in seconds, says Srinivasa R. Raghavan, assistant professor in the department of chemical and biomolecular engineering. Light also can markedly increase the viscosity of other fluids, he adds.
For the current systems, the viscosity changes are irreversible, he notes. The next logical step is to develop inexpensive fluids whose viscosity changes are reversible, he says. Another goal is to markedly increase the speed of the viscosity change. Raghavan expects that speeds of milliseconds are possible. He foresees uses for such fluids at the micro- or nano-scale, for instance, in valves to control other fluids. At such scales, he reckons a reasonable amount of material would cost only pennies.