Evaporation, Lifetime, and Robustness Studies of Liquid Marbles for Collision-Based Computing

Liquid marbles (LMs) have recently attracted interest for use as cargo carriers in digital microfluidics and have successfully been implemented as signal carriers in collision-based unconventional computing circuits. Both application domains require LMs to roll over substantial distances and to survive a certain number of collisions without degrading. To evaluate the lifetime of LMs being subjected to movement and impact stresses, we have selected four types of coating to investigate: polytetrafluoroethylene (PTFE), ultrahigh density polyethylene (PE), Ni, and a mixture of Ni with PE (Ni–PE). Hierarchies of robustness have been constructed which showed that pure PE LMs survived the longest when stationary and in motion. Pure PTFE LMs were shown to be the least resilient to multiple impacts. The PTFE coating provided minimal protection against evaporative losses for small LM volumes (2 and 5 μL) however, larger LMs (10 μL) were shown to have good evaporative stabilities when stationary. Conversely, PE LMs showed a remarkable ability to withstand multiple impacts and were also stable when considering just passive evaporation. Hybrid Ni–PE LMs exhibited more resilience to multiple impacts compared to Ni LMs. Thus, when designing LM devices, it is paramount to determine impact pathways and select appropriate coating materials.