Multicomponent Interfacial Assemblies: Tailoring Surface Heterogeneities

Imagine having liquid droplets with thin, soft shells and patches on their surfaces. When these droplets meet one another, patches with similar properties form contact points between the droplets and direct the ways in which the droplets organize. In areas where contact is made, molecules or ions can be transferred from one droplet to another. This produces systems that controllably transfer substances or that produce electrical current based on ion flow. This project will create novel systems built from liquid droplets and large molecules, where the droplets organize themselves based on favorable surface interactions. The project will uncover new, fundamental knowledge needed to build stable, interacting droplets that, instead of merging, create tiny filters in between them. In addition, the project will help educate students as they prepare to enter the U.S. workforce as technical experts in STEM fields. Polymeric materials composed of unconventional architectures, such as bottlebrush polymers that are the focus of this project, present new opportunities to perform precise interfacial studies and provide a fundamental understanding in the engineering of colloidal and fluidic structures. The bottlebrush polymers synthesized in the project, in essence comprising soft nanoparticles, contain hydrophobic and hydrophilic side-chains, the composition and arrangement of which are designed to drive segregation to the surface of droplets (oil-in-water or water-in-oil emulsion droplets), thereby reducing interfacial tension and setting up routes to form droplets with unique structures and functions. By employing mixtures of different bottlebrush polymers, interfacial phase-separation will create microdomains on droplet surfaces, with dimensions that are dictated by polymer stoichiometry and the time scale of phase-separation. Access to even smaller (nanoscale) domains will be achieved by covalently linking the bottlebrush polymers into block-like structures. Moreover, bottlebrush polymers with ultrathin, raft-like architectures will be studied for their advantageous interfacial coverage, in which interfacial gaps enable ion transport in droplet interface bilayers. The ability to generate current from ion transport in these droplet assemblies holds potential to engineer new types of artificial neuromorphic systems from well-defined and scalable polymers. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.