DESIGNING MICROSCOPIC PARTICLES THAT DESIGNING MICROSCOPIC PARTICLES THAT SWIM AND SELF-ORGANIZE FAR FROM EQUILIBRIUM USING CHEMICAL FUELS AND ACOUSTIC FIELDSSWIM AND SELF-ORGANIZE FAR FROM EQUILIBRIUM USING CHEMICAL FUELS AND ACOUSTIC FIELDS

The most impressive, desirable, and “life-like” features of biological systems arise because they exist far from thermodynamic equilibrium. That is, in contrast to inanimate materials, organisms maintain a dynamic steady state by constantly consuming, utilizing, and interacting with chemical fuels. This behavior gives rise to highly sought-after properties, such as complex self-organization over multiple length scales, feedback responsiveness, self-optimization, memory, and micro- and macroscopic motion. By understanding non-equilibrium interactions between autonomously moving, microscopic synthetic particles that are powered by chemical fuels and external fields, it may be possible to design abiotic model systems with similar emergent and life-like properties. However, these interactions are underexplored because of the poor scalability of micromotor synthesis and a limited toolbox of weak forces. To this end, we have explored bubble-based nano- and microscopic swimmers by developing scalable fabrication methods and analyzing the strong forces they generate when they are powered by ultrasound. This has led to novel capabilities in micromanipulation, as well as the opportunity to observe particles that spontaneously self-assemble and navigate their environment geometrically. Additionally, we have used advanced synthesis and microscopic analysis to study the motion of bimetallic nanorods at acoustic levitation planes, allowing us to develop a unifying theory for how these nanoparticles self-propel. We also address scaling laws of enzyme-based micropumps experimentally and computationally to examine their viability in creating nanoscale pumps for microfluidic applications. Finally, in a collaborative project with the Kagan group, we designed microscopic spinners that move autonomously at acoustic standing waves. Collections of hundreds of these spinners show the first experimental evidence of rotation-induced phase separation, which is governed by hydrodynamic coupling. Rotor chirality leads to 3D hierarchical self-organization and formation of up to six coexisting non-equilibrium phases. These simple examples demonstrate new methods to drive not only motion, but also communication between microscopic particles under tunable and switchable non-equilibrium conditions, capabilities that could lead to the realization of new systems with macroscopically useful collective properties.