Inter-droplet Membranes for Mechanical Sensing Applications

This dissertation combines self-assembly phenomena of amphiphilic molecules with soft materials to create and characterize mechanoelectrical transducers and sensors whose sensing elements are thin-film bioinspired membranes comprised of phospholipids or amphiphilic polymers. We show that the structures of these amphiphilic molecules tune the mechanical and electrical properties of these membranes. We show that these properties affect the mechanoelectrical sensing characteristic and range of operation of these membrane transducers. In the experiments, we construct and characterize a membrane-based hair cell embodiment that enables the membrane to be responsive to mechanical perturbations of the hair. The resulting oscillations of membranes formed between droplets produces measurable current due to the time rate of change of the electrical capacitance of the vibrating membranes. In addition to sensors that feature a single membrane between two droplets, we also study mechanoelectrical transduction in multi-membrane, multi-hair Droplet Interface Bilayer (DIB) array networks formed from more than two droplets. In this work, we show for the first time that multi-membrane Droplet Interface Bilayer (DIB) networks can be used to enhance the sensitivity and frequency selectivity of these sensors.

Therefore, we utilized the same self-assembly phenomena to form more stable and robust interfaces between droplet using synthetic polymers. Copolymer Stabilized Interfaces (CSIs) are formed between triblock polymer-coated aqueous droplets in alkanes and silicone oil, and we demonstrate that, unlike lipid-coated droplets, triblock-coated droplets do not spontaneously adhere in oil when the organic phase is a good solvent for the hydrophobic PDMS block.

Interestingly, a thinned planar membrane between droplets can be reversibly formed upon the application of sufficient voltage across the interface, which we believe works to remove excess solvent through electro-compression. These results thus show new capability for initiating, controlling, and disconnecting polymer-stabilized membranes between aqueous droplets. These membranes also exhibit wider range of airflow operation when used to construct a hair cell sensors.