Executive Summary : | Unlike Brownian particles, synthetic active particles offer better control over colloidal motion, hence they offer great potential to be used as drug delivery agents, autonomous de-pollutants and micro-robots. Therefore, there is an active global interest in fundamentally understanding different physical aspects of their motion in varied environments. For most of the envisaged applications, the surrounding media (colloidal suspensions, foams and emulsions, polymeric solutions, blood, cervical mucus saliva etc.) generally is a complex fluid that contains particulates and/or biopolymers. However, so far, the motion of active particles has been primarily studied in quiescent bulk or at the interfaces of Newtonian fluids where stress is dissipative and the inter-particle hydrodynamics is relatively simple and the dynamics of active particles in such complex surroundings, has not been well addressed. Complex fluid environments exhibit viscoelastic properties different from simple Newtonian fluids, and the reciprocal coupling of colloidal dynamics with the rheological and structural properties of the fluid may result in rich and distinct phenomenology. Additionally, the presence of any external flow perturbation is ubiquitous for most of the potential applications generating a local shear environment. However, so far, much effort, indeed, has been devoted to the understanding of motion of synthetic active colloids in a quiescent media and synthetic active colloids residing in flow have been overlooked.
In order to develop a complete understanding of the effect of external flow and viscoelasticity of the complex media on colloid's active propulsion, in this proposal, we aim to investigate the motion of active colloids in flowing complex non-Newtonian fluids. Specifically, we will try to decipher the effect of ambient flow coupled with the elastic stresses generated in the viscoelastic media due to the active transnational motion on the rotational tendency of the particle which eventually dictates the direction of its trajectory. In this project, we will synthesise Janus particles (Pt-SiO? and Au-TiO?) of approximately 5 diameter using shadowing method. These Janus particles will be dispersed in different polymeric solutions with varying viscoelastic properties and varying shear velocities in micro-capillaries. The particles will be propelled using the self-diffusiophoresis mechanism by adding H?O? or exposure of UV light. The active motion of Janus particles will be investigated through Single Particle tracking experiments using an optical microscope where mean square displacement of the particles' trajectory with time elapsed will be captured. Particles' diffusivity (D), propulsion velocity (v) and rotational time (tau) will be computed using which we aim to understand the precise effect of surrounding medium's elasticity and shear flow on the motion of the active particles. |