On-Demand Activation of Thin Alginate Shell Encapsulated Volatile Liquid for Untethered Pneumatic Soft Actuation

Abstract:

Phase-changing liquids in elastomeric matrices have drawn attention for facilitating pneumatic actuators that circumvent the need for tethering in soft robotics. Phase change from liquid to vapor enables high-power, self-contained actuation triggered by minimal temperature change. However, due to the volatile nature of the phase-changing liquids, simple fabrication methods that ensure both long-term volatile liquid storage and reliable on-demand activation are beneficial. We present a straightforward method for encapsulating Novec7000, a nonhazardous volatile liquid with a boiling point of 34°C, within micron-thin alginate shells. The alginate-Novec7000 capsules are prepared through in situ injection of Novec7000 during ionic crosslinking of sodium alginate, followed by ambient drying. These capsules remain intact during extended storage (over 7 months) and can be activated on-demand either mechanically (with two to six newtons of compressive force) or thermally (above the volatile liquid's boiling point). This approach prevents the loss of volatile liquids for pneumatic phase-change soft robots until actuation is desired. Demonstrations highlight alginate-Novec7000 capsule utility in embedding volatile liquids into elastomeric matrices, enabling thermally activated pneumatic valves used as a high-temperature safeguard in pipe systems. On-demand release of volatile liquids can expand the utility of untethered self-contained pneumatic phase-change soft robotics and enable new applications.

Keywords:

Alginate, capsule, shell fracture, soft robotics, untethered pneumatic actuators