(Invited) ALD-Based Infiltration and Growth of Inorganic Materials in Polymers

Abstract

Sequential infiltration synthesis (SIS) has emerged in the past decade as a powerful technique for growth of inorganic materials within polymers through atomic layer deposition (ALD) chemistry. In SIS, ALD precursors diffuse into the polymer and interact with it, leading to inorganic materials growth within the polymer’s free volume. If desired, the polymer can later be removed, yielding polymer-templated inorganic structures. Combining SIS with self-assembled block copolymer (BCP) patterns results in selective growth of inorganic materials within the polar domains of the BCP, making it an attractive method for directed templating of inorganic nanostructures. Thus, SIS opens a pathway for exploiting ALD precision and rich materials library in new 3D morphologies, defined by the polymer.To build SIS design rules and expand SIS’ possibilities, we probed SIS growth and evolution at the atomic scale and explored the role of reversible polymer-precursor interactions in SIS growth through a plethora of methods: in-situ growth analysis (microgravimetry and FTIR), ex-situ high-resolution electron microscopy and extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT) calculations. This knowledge was then applied in fabrication by design of metal oxide fibers, porous particles, and membranes.We fabricated Al2O3 and ZnO nanofibers, nanobelts, and core-shell fibers using designed growth profiles within electrospun polymer fibers. By controlling the organometallic precursors’ diffusion time, simultaneous but spatially controlled growth of Al2O3 and ZnO within the fibers was achieved, leading to the formation of metal oxide core-shell fibers. Self-assembled BCP particles were used to template porous metal oxide particles by selective growth of Al2O3 in the major block of the self-assembled structure. The uniform BCP assembly led to uniporous pores in the metal oxide particles. Finally, we utilized SIS and ALD within and onto BCP membranes for exceptional pore size control and pores’ surface engineering, yielding highly selective filtration membranes.