From the Labs: Materials

New publications, experiments and breakthroughs in materials--and what they mean.

Reactions on Demand

Light-Activated These nylon capsules, filled with chemical reactants and carbon nanotubes, heat up and burst when irradiated with a laser. Credit: Stefan Pastine and David Okawa

Microcapsules isolate reactants until a laser bursts the bubble.

Results: Researchers at the University of California, Berkeley, enclosed highly reactive chemicals in polymer microcapsules. They showed that the capsules can be burst using light from a laser, allowing the chemicals to escape and react with each other to form a desired product.

Why it matters: The microcapsules will enable chemists to place reactants in precise locations before triggering them to react. Scientists could also initiate reactions at precisely timed intervals. These techniques could be useful in applications such as timed drug delivery inside the body, printing, and self-healing materials.

Methods: The chemical to be encapsulated is mixed with a small quantity of carbon nanotubes and with the chemical precursors of nylon, which form nylon microspheres as the mixture is stirred. As they form, the spheres capture the nanotubes and the chemical reactant. When the researchers shine a red laser on the capsules, the nanotubes absorb the energy and heat up until the capsules burst. In a proof- of-concept experiment, the researchers made microcapsules that contained a special catalyst and suspended them in a reactive liquid. The microcapsule protected the catalyst and the liquid from reacting; however, when a laser was used to burst the capsules, the catalyst was released and quickly transformed the liquid into a solid.

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Next steps: The group is testing reaction capsules that contain dyes instead of nanotubes to absorb the laser energy; the dyes respond to specific bandwidths of light, such as red, green, or blue. This could allow scientists to control reactions more precisely by shining different colors of light at different times.

Source: “Chemicals on Demand with Phototriggerable Microcapsules” by Jean M.J. Fréchet et al.; Journal of the American Chemical Society 131: 13586–13587