Large-Area Uniaxial-Oriented Growth of Free-Standing Thin Films at the Liquid-Air Interface with Millimeter-Sized Grains

Manipulating materials at the atomic scale and assembling them into macroscopic structures with controlled dimensionalities and single-crystal quality are grand scientific challenges. Here, we report a general solvent evaporation method to synthesize large-area uniaxial-oriented growth of free-standing thin films at the liquid-air interface. Crystals nucleate at the solution surface and rotate into the same orientation under electrostatic interaction and then merge as large crystals and grow laterally into a large-area uniform thin film with millimeter-sized grains. The lateral dimension is confined only by the size of containers. The film thickness can be tuned by adjusting solvent evaporation rate (R) and solute diffusivity (D), and a characteristic length, L * ∼ D R , was derived to estimate the film thickness. Molecular dynamic (MD) simulations reveal a concentration spike at the liquid-air interface during fast solvent evaporation, leading to the lateral growth of thin films. The large-area uniaxial oriented films are demonstrated on both inorganic metal halides and hybrid metal halide perovskites. The solvent evaporation approach and the determination of key parameters enabling film thickness prediction are beneficial to the high throughput and scalable production of single crystal-quality thin film materials under controlled evaporation conditions.

Solute Transport Dependence on 3D Geometry of Hydrogel Networks

Hydrogels are used in drug delivery applications, chromatography, and tissue engineering to control the rate of solute transport based on solute size and hydrogel-solute affinity. Ongoing modeling efforts to quantify the relationship between hydrogel properties, solute properties, and solute transport contribute toward an increasingly efficient hydrogel design process and provide fundamental insight into the mechanisms relating hydrogel structure and function. However, here we clarify previous conclusions regarding the use of mesh size in hydrogel transport models. We use 3D geometry and hydrogel network visualizations to show that mesh size and junction functionality both contribute to the mesh radius, which determines whether a solute can diffuse within a hydrogel. Using mesh radius instead of mesh size to model solute transport in hydrogels will correct junction functionality-dependent modeling errors, improving hydrogel design predictions and clarifying mechanisms of solute transport in hydrogels.