How to Use Kelvin Forces to Dynamically Tune the Interaction Between Colloids and Dipolar Polymers ^†

Using Langevin Dynamic simulations, we show two examples of how the competition between entropic forces and interactions arising from the mismatch between the non-polar and dipolar moieties present in a medium (Kelvin Forces) can be used to tune the interaction between colloids and polymers via an external field. Our results are important for both electric and magnetic systems. In the first example [1], we show that it is possible to create dipolar polymer brushes whose interaction with colloidal particles can be switched from repulsive to attractive by simply adjusting the strength of the external field. This effect can be used in polymer brush applications in which the entrapping and retention of colloidal particles for later release is required. In the second example [2], we show that the depletion interaction of colloidal particles immersed in a bath of dipolar polymers can be also modulated using an external field. In many cases, it is possible to switch from typical depletion force profiles between two colloidal particles to force profiles that contain one or several stationary points depending on the strength of the external field. Furthermore, the inter-particle distance at which these stationary points occur can also be controlled to a certain extent by adjusting the strength of the external field. These findings can be useful in the development of magnetic colloidal tweezers and colloidal ratchets.