We present a design for polymer capsules that exhibit a range of unusual autonomous behavior when exposed to a chemical fuel. The capsules have a physically gelled core loaded with catalytic particles and a shell composed of a chemically crosslinked polymer. In the presence of the fuel, a catalytic reaction occurs, which generates oxygen gas. The gas collects in a zone between the core and the shell, and the resulting gas pressure causes the shell to stretch. As the capsule inflates, the chain segments in the shell are stretched more until a point is reached when further stretching is not possible. At this point, the shell ruptures. Shells that are more densely crosslinked rupture in a shorter time. Three rupture modes are documented: gentle, moderate, and violent. The latter involves the core being forcefully ejected out of the shell in a manner similar to the ejection of needles out of nematocyst cells present on jellyfish. A further unusual phenomenon is observed when the above capsules are loaded with a solute (dye). In the presence of the chemical fuel, we show that the capsule behaves like a ‘beating heart’ and its surface pulses outward and inward in the transverse direction. In turn, the solute in the capsule is released in a series of periodic pulses. We hypothesize that a binding reaction between the dye and the catalytic particles is the key to explaining these results.

Capsules that exhibit spontaneous inflation, core ejection, and pulsed release of solute

2019 Spring National Meeting

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