Propulsion of catalytic Janus spheres in viscosified solutions

Many applications of Janus motors involve moving objects through complex environments that are mixtures of components. The flow properties of these mixtures could be Newtonian or non-Newtonian. In other applications, additives may be introduced as a way of controlling the motion of motors. The first step in understanding how the fluid mixtures alter their motion is to examine propulsion in fluids where additives change the shear viscosity while the fluid remains Newtonian. We show how solution viscosity affects Janus motor propulsion keeping all other factors (motor size, fuel concentration, temperature, etc.) constant. The velocity is shown to decay approximately inversely with viscosity. Further, the type of viscosifier used affects the interaction between fuel molecules and motor, which affects propulsion. This is part of the overall goal of understanding how solution properties impact propulsion independent of a particular application. When qualifying the propulsion in crowded environments, it is important to understand how to accurately quantify the response. We have used computer simulations to quantify the errors associated with particle tracking when extracting the propulsion of Janus motors.