# Stokesian dynamics of pill-shaped Janus particles with stick and slip boundary conditions

## TL;DR

This paper investigates how pill-shaped Janus particles with mixed boundary conditions experience forces and torques in a fluid flow, revealing unique behaviors depending on their shape and slip properties.

## Contribution

It introduces a boundary integral method to analyze forces and torques on Janus particles with mixed boundary conditions in Stokes flow, highlighting novel sign-changing transverse forces.

## Key findings

- Force transverse to flow can change sign depending on aspect ratio and slip length.
- The boundary integral formulation effectively handles singularities in the analysis.
- Unique properties arise from the Janus nature of the particles.

## Abstract

We study the forces and torques experienced by pill-shaped Janus particles of different aspect ratios where half of the surface obeys the no-slip boundary condition and the other half obeys the Navier slip condition of varying slip lengths. Using a recently developed boundary integral formulation whereby the traditional singular behaviour of this approach is removed analytically, we quantify the strength of the forces and torques experienced by such particles in a uniform flow field in the Stokes regime. Depending on the aspect ratio and the slip length, the force transverse to the flow direction can change sign. This is a novel property unique to the Janus nature of the particles.