Magnetophoretic measurement of the drag force on partially immersed microparticles at air–liquid interfaces

The drag force on magnetic microparticles moving along air–liquid interfaces in a magnetic field was determined by trajectory analysis. The drag force in such a system is important for magnetic targeting and retention of drug particles in the airways. For pure, Newtonian liquids, it was shown that the theoretical predictions of drag force found in the literature are consistent with experimental results at low contact angles and high bulk viscosities. As such, these models can be used to predict drag due to bulk viscosity on particles in the airways. In surfactant solutions (water and SDS), it was found that the drag coefficient of the particle varies depending on the surfactant concentration and particle velocity, due to the interplay of particle motion and surfactant concentration. The drag coefficient on the particles when surfactants are present is a function of the particle velocity in addition to the interface properties. This behavior is also significant for drug delivery in the airways, as it would restrict the aggregation of deposited particles, increasing the magnetic field required for particle retention.