The role of slip velocity in determining particle migration in viscoelastic microchannel flow

We investigated the influence of the slip velocity on particle migration in viscoelastic microchannel flows using a hybrid computational approach that coupled the lattice Boltzmann method with coarse-grained molecular dynamics. Our results demonstrate that the slip velocity changes lateral migration mechanisms by affecting the balance of inertial and elastic lift forces. In Newtonian fluids, forward slip drives particles toward the channel walls due to dominant inertial lift, while backward slip promotes migration toward the channel centreline. In viscoelastic fluids, however, slip-induced elastic lift forces arising from asymmetric polymer deformation around particles exceed inertial effects by an order of magnitude. This leads to a complete reversal of migration behaviour. We established that elastic lift scales linearly with the slip velocity and the block ratio, consistent with theoretical predictions, while polymer chain length influences elastic lift through a power-law dependence ( $F_{e,s}^*\sim M^{1.66}$ ). These findings reveal that viscoelasticity-mediated slip effects provide a robust mechanism for particle manipulation in complex fluids. By connecting the microscopic polymer dynamics to macroscopic transport phenomena, our work offers new design principles for particle sorting and focusing applications in microfluidic systems.