Single-walled aluminosilicate nanotubes are attractive materials for construction of nanofluidic devices. They have a well-defined structure, a hydrophilic interior with periodic wide and narrow regions, precisely tunable length and diameter, and a functionalizable interior for tuning mass transport and adsorption properties. We report a computational and experimental investigation that highlights the unique adsorption and diffusive water transport properties of these nanotubes. Axial self-diffusivities of water molecules (at loadings ranging from near-infinite dilution to near-saturation) are calculated by molecular dynamics (MD) simulations, whereas adsorption properties are computed with grand canonical Monte Carlo (GCMC) simulations and are also compared to experimental data. The transport diffusivities are evaluated through the Darken approximation. Water transport in these nanotubes at room temperature was observed to occur via Fickian diffusion. The self-diffusivity decreases with an increase in water content, whereas the transport diffusivity exhibited a maximum at intermediate water content. The diffusivities were comparable to the diffusivity of bulk liquid water and hence are considerably higher than in other nanoporous aluminosilicates such as zeolites. The computed adsorption isotherms exhibited inflections at low partial pressures (∼6 mm Hg) with a large fraction of adsorption occurring in the pores of the nanotube displaying remarkable hydrophilicity. As a combined result of the relatively fast Fickian diffusion of water, hydrophilicity of the nanotubes, and short nanotube lengths, the diffusive water flux through an aluminosilicate nanotube film is predicted to be quite high (10 2 -10 3 mol m -2 s -1 ), even at very low pressure differentials across the membrane.

The fabrication, detailed characterization, and molecular transport properties of nanocomposite membranes containing high fractions (up to 40 vol %) of individually-dispersed aluminosilicate single-walled nanotubes (SWNTs) in poly(vinyl alcohol) (PVA), are reported. The microstructure, SWNT dispersion, SWNT dimensions, and intertubular distances within the composite membranes are characterized by scanning and transmission electron microscopy (SEM and TEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), XRD rocking curve analysis, small-angle X-ray scattering (SAXS), and solid-state NMR. PVA/SWNT nanocomposite membranes prepared from SWNT gels allow uniform dispersion of individual SWNTs in the PVA matrix with a random distribution of orientations. SAXS analysis reveals the length (∼500 nm) and outer diameter (~2.2 nm) of the dispersed SWNTs. Electron microscopy indicates good adhesion between the SWNTs and the PVA matrix without the occurrence of defects such as voids and pinholes. The transport properties of the PVA/SWNT membranes are investigated experimentally by ethanol/water mixture pervaporation measurements, computationally by grand canonical Monte Carlo and molecular dynamics, and by a macroscopic transport model for anisotropic permeation through nanotube-polymer composite membranes. The nanocomposite membranes substantially enhance the water throughput with increasing SWNT volume fraction, which leads to a moderate reduction of the water/ethanol selectivity. The model is parameterized purely from molecular simulation data with no fitted parameters, and shows reasonably good agreement with the experimental water permeability data.

Co-evaporation of Cu-KF-In-Se was performed on substrates with varied surface Na compositions. Compositions of interest for photovoltaic absorbers were studied, with ratios of (K+Cu)/In ~ 0.85 and K/(K+Cu) ~ 0 -0.57. Soda-lime glass (SLG) substrates led to the most Na by secondary ion mass spectrometry, while SLG/Mo and SLG/SiO2/Mo substrates led to 3x and 3,000x less Na in the growing film, respectively.Increased Na content favored Cu1-xKxInSe2 (CKIS) alloy formation by X-ray diffraction (XRD), while decreased Na favored the formation of CuInSe2 + KInSe2 mixed-phase films. Scanning electron microscopy and energy dispersive X-ray spectroscopy revealed the KInSe2 precipitates to be readily recognizable planar crystals. Extrinsic KF addition also drove diffusion of Na out from the various substrates and into the growing film, in agreement with previous reports. Time-resolved photoluminescence showed enhanced minority carrier lifetimes for films with moderate K compositions (0.04 < K/(K+Cu) < 0.14) grown on Mo. Due to the relatively high detection limit of KInSe2 by XRD and the low magnitude of chalcopyrite lattice shift for CKIS alloys with these compositions, it is unclear if the lifetime gains were associated with CKIS alloying, minor KInSe2 content, Highlights  Increased substrate Na favored Cu1-xKxInSe2 formation  Decreased substrate Na favored the formation of CuInSe2 + KInSe2 mixed-phase films  Extrinsic KF addition drove Na diffusion out from the substrate  Moderate K compositions on Mo substrates had enhanced minority carrier lifetimes Keywords A1. Crystal morphology; A1. Segregation; A1. Solid solutions; A3. Physical vapor deposition processes; B1. Alloys; B2. Semiconducting materials