Single-Walled Aluminosilicate\nNanotube/Poly(vinyl\nalcohol) Nanocomposite Membranes

Abstract

The fabrication, detailed characterization, and molecular\ntransport\nproperties of nanocomposite membranes containing high fractions (up\nto 40 vol %) of individually-dispersed aluminosilicate single-walled\nnanotubes (SWNTs) in poly­(vinyl alcohol) (PVA), are reported. The\nmicrostructure, SWNT dispersion, SWNT dimensions, and intertubular\ndistances within the composite membranes are characterized by scanning\nand transmission electron microscopy (SEM and TEM), energy-dispersive\nspectroscopy (EDS), X-ray diffraction (XRD), XRD rocking curve analysis,\nsmall-angle X-ray scattering (SAXS), and solid-state NMR. PVA/SWNT\nnanocomposite membranes prepared from SWNT gels allow uniform dispersion\nof individual SWNTs in the PVA matrix with a random distribution of\norientations. SAXS analysis reveals the length (∼500 nm) and\nouter diameter (∼2.2 nm) of the dispersed SWNTs. Electron microscopy\nindicates good adhesion between the SWNTs and the PVA matrix without\nthe occurrence of defects such as voids and pinholes. The transport\nproperties of the PVA/SWNT membranes are investigated experimentally\nby ethanol/water mixture pervaporation measurements, computationally\nby grand canonical Monte Carlo and molecular dynamics, and by a macroscopic\ntransport model for anisotropic permeation through nanotube–polymer\ncomposite membranes. The nanocomposite membranes substantially enhance\nthe water throughput with increasing SWNT volume fraction, which leads\nto a moderate reduction of the water/ethanol selectivity. The model\nis parameterized purely from molecular simulation data with no fitted\nparameters, and shows reasonably good agreement with the experimental\nwater permeability data.