Boundary effects on the locomotion of active Janus particles

Self-propelled or “active” micrometer scale particles are capable of supplying local mechanical work, necessary for microscale cargo delivery and useful in other applications within bioimaging and sensing. Research in the last decade has focused on developing, measuring, and manipulating the locomotion mechanisms of active particles in simple environments. However, many applications will be in complex environments with nearby boundaries or variations in physiochemical cues. This poster reports the directed motion of platinum coated polystyrene particles at infinite dilution in the presence of H2O2, which acts as a fuel to drive motion. A transport mechanism called “diffusiophoresis” drives motion of the particle as a consequence of the local gradient in chemical species following the breakdown of hydrogen peroxide into oxygen and water on the platinum cap. The apparent swimming speed of the particle increased from 0 m/s to approximately 2 m/s with fuel concentrations between 0% and 10% near a boundary. Complementary simulation work showed clustering as a consequence of the balance between swimming speed and random Brownian diffusion. Finally, the poster will summarize efforts to tune swimming speed by adjusting the physiochemical environment of the particle via the addition of salt and non-adsorbing nanoparticles. Results from this work demonstrate how the local environment will alter the dynamic behavior of active Janus particles.https://engagedscholarship.csuohio.edu/u_poster_2018/1069/thumbnail.jp

Charged Nanoparticles Quench the Propulsion of Active Janus Colloids

Active colloidal particles regularly interact with surfaces in applications ranging from microfluidics to sensing. Recent work has revealed the complex nature of these surface interactions for active particles. Herein, we summarize experiments and simulations that show the impact of charged nanoparticles on the propulsion of an active colloid near a boundary. Adding charged nanoparticles not only decreased the average separation distance of a passive colloid because of depletion attraction as expected but also decreased the apparent propulsion of a Janus colloid to near zero. Complementary agentbased simulations considering the impact of hydrodynamics for active Janus colloids were conducted in the range of separation distances inferred from experiment. These simulations showed that propulsion speed decreased monotonically with decreasing average separation distance. Although the trend found in experiments and simulations was in qualitative agreement, there was still a significant difference in the magnitude of speed reduction. The quantitative difference was attributed to the influence of charged nanoparticles on the conductivity of the active particle suspension. Follow-up experiments delineating the impact of depletion and conductivity showed that both contribute to the reduction of speed for an active Janus particle. The experimental and simulated data suggests that it is necessary to consider the synergistic effects between various mechanisms influencing interactions experienced by an active particle near a boundary

Charged Nanoparticles Quench the Propulsion of Active Janus Colloids

Active colloidal particles regularly interact with surfaces in applications ranging from microfluidics to sensing. Recent work has revealed the complex nature of these surface interactions for active particles. Herein, we summarize experiments and simulations that show the impact of charged nanoparticles on the propulsion of an active colloid near a boundary. Adding charged nanoparticles not only decreased the average separation distance of a passive colloid because of depletion attraction as expected but also decreased the apparent propulsion of a Janus colloid to near zero. Complementary agentbased simulations considering the impact of hydrodynamics for active Janus colloids were conducted in the range of separation distances inferred from experiment. These simulations showed that propulsion speed decreased monotonically with decreasing average separation distance. Although the trend found in experiments and simulations was in qualitative agreement, there was still a significant difference in the magnitude of speed reduction. The quantitative difference was attributed to the influence of charged nanoparticles on the conductivity of the active particle suspension. Follow-up experiments delineating the impact of depletion and conductivity showed that both contribute to the reduction of speed for an active Janus particle. The experimental and simulated data suggests that it is necessary to consider the synergistic effects between various mechanisms influencing interactions experienced by an active particle near a boundary