Synthetic microswimmers are small objects with the size of micrometers. Autonomous motion, i.e., driven and directed (i) rotation, (ii) vibration/oscillation or (iii) translation (locomotion), requires the particles to do work. Our example exploits a controlled body shape deformation for the motility, mimicking the locomotion of bacteria. Because of the low Reynolds number conditions, the forward stroke must be different from the shape recovering stroke. The repetion is firstly controlled from outside in a second approach generated autonomously.<br/>For this we designed a LCST-hydrogel system, in which the motion is affected by volume change and bending of the micro object. It is controlled precisely by the (i) design of the geometrical shape, (ii) the widely variable material properties and (iii) by the energy intake via infrared irradiation. We attempted and succeeded to cause the repetitive deformation by continuous irradiation. This required the introduction of an autonomous feed-back mechanism by which the energy uptake ceased upon raising the temperature and a hysteretic bistability by which we could prevent that the system could adopt a shape corresponding to a steady state equilibrium. The volume-phase transition is affected by strictly localized heating inside the particles. For this purpose, the gels were equipped with 1-4 gold nanorods per mm<sup>3</sup> that absorb light at 780 nm and convert it practically instantaneously to heat. The critical phase segregation occurs within milliseconds and that the dynamics and the change in shape can be designed by the geometrical hydrogel structure.

Can a material perform as an engine?

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.