Sessile nanofluid droplet can act like a crane

Interactive droplet systems form the backbone for emerging avenues in droplet based technologies like cell sorting, inkjet printing and digital microfluidics, to name a few. These and their associated fields have gained significant importance in the recent times. Here, we report one such phenomenon wherein a naturally evaporating nanocolloidal sessile droplet interacts with a porous silica gel bead to mimic a macro scale mechanical crane assembly. Precisely, we show a sequence of events displayed by the particle laden aqueous droplet (nanoparticles of silica at different loading rates placed on a hydrophobic substrate) when brought in contact with a meso-porous silica gel bead. First, preferential self-assembly along droplet-bead interface is followed by formation of an adhesive bond. The phenomenon continues until the evaporating droplet naturally lifts the bead. The kinematics of the lift mechanism can be represented by a simple four bar linkage. This work provides insights into interactions between droplets and freely placed porous objects across multiple spatio-temporal scales. Present study should not just motivate researchers to design interactive droplet based systems but also use the same to perform engineering tasks like the crane action.