(600g) Assembly and Scaffolding Strategies for Realizing Ultra-Thin Inorganic Films with Tunable Porosity

Porous thin films scalable to tens of nanometers in thickness with tunable hierarchy in pore size and topology hold exciting technological implications spanning, among others, high-selectivity and high-flux membrane separations to rapid-response sensors selective for large and small target molecules.  Owing to their inherent microporosity, inorganic materials such as zeolites, carbons, and some nanoparticle assemblies, hold specific promise in such applications where molecular selectivity is critical.  Yet, control over porous film thickness has been a persistent challenge for films composed of such materials and supported on porous or non-porous substrates, leading in some cases to stress-induced crack formation and sluggish molecular flux.  We address the challenge of controlling film thickness of porous inorganic films, and in some cases controlling underling porosity of these films, through a hierarchical templating strategy rooted in convective deposition of tunable nanoparticles and subsequent replication and materials scaffolding techniques.  Specifically, we will address three classes of porous thin films scalable to just tens of nanometers in thickness: convectively deposited nanoparticulate colloidal crystalline films, carbon replica films characterized by either ordered mesoporosity or asymmetric mesopore-supported ultra-thin microporous layers, and (sacrificial) carbon-scaffolded ultra-thin zeolite films (e.g., silicalite-1, SAPO-34) composed of extensive high-aspect-ratio single-crystal domains.  We will describe stages in film formation, sensitivity of film properties to synthesis conditions, transition from non-porous to highly-porous substrates as film supports, and the role of pore topology in thin film scaffolding.  We will describe critical structure-property relations governing porous film performance with regards to achievable molecular selectivity and flux towards establishing proof-of-principle application of this synthesis approach to a broader class of porous inorganic materials.