# Dipolar Brush Polymers: A Numerical Study of the Force Exerted onto a Penetrating Colloidal Particle Under an External Field

## TL;DR

This paper uses simulations to study how external fields affect forces on particles near dipolar polymer brushes, revealing regions of attraction and repulsion.

## Contribution

The study identifies tunable force barriers and stationary points in dipolar polymer brushes under external fields.

## Key findings

- Force profiles show a barrier at large distances and lower repulsion at shorter distances.
- Net attractive forces and stationary points can emerge with specific polymer and field parameters.
- The behavior is explained by competition between steric and dipolar Kelvin forces.

## Abstract

Langevin Dynamics numerical simulations have been used to compute the force profiles that dipolar polymer brushes exert onto a penetrating colloidal particle. It has been observed that force profiles are strongly influenced by externally applied fields: at large distances from the grafting surface, a force barrier appears, and at shorter distances a region with lower repulsive forces develops. Furthermore, with the right combination of polymer grafting density, polymer chain length and strength of the external field, it is possible to observe in this intermediate region both the existence of net attractive forces onto the penetrating particle and the emergence of a stationary point. The existence of these regions of low repulsive or net attractive forces inside the dipolar brushes, as well as their dependence on the different parameters of the system can be qualitatively reasoned in terms of a competition between steric repulsion forces and Kelvin forces arising from the dipolar mismatch between different regions of the system. The possibility to tune force profile features such as force barriers and stationary points via an external field paves the way for many potential surface–particle-related applications.