Experimental Measurement of near-Field Capillary Interactions Between Rod-Like Particles

Micrometer-sized cylinders at fluid interfaces self-assemble owing to capillary interactions, forming linear chains of particles joined end-to-end by ‘capillary bonds’. We measure the strength of these capillary bonds by a new experimental technique. We incorporate a magnetic cylinder within a self-assembled chain of regular non-magnetic cylinders. Upon application of a rotating external magnetic field, the magnetic cylinder experiences a localized magnetic torque, which causes in-plane rotation of the entire chain. From the balance of viscous resistance and capillary forces, and from the observed deformation of the linear chain, important information about the chain mechanics can be extracted.  These experiments are compared to predictions based on numerical simulation of capillary bonds between cylinders.  These results have implications for particle-stabilized emulsions, interfacial gels and encapsulation of materials within particle stabilized drops.