Thickness-Dependent Swelling of Molecular Layer-by-Layer Polyamide Nanomembranes

The thickness-dependent water vapor swelling of molecular layer-by-layer polyamide films is studied via specular X-ray reflectivity. The maximum swelling ratio of these ultrathin films scale inversely with thickness but more importantly show a dual-mode sorption behavior characterized by Langmuir-like sorption at low relative humidity and network swelling at high relative humidity. The thickness-dependent network parameters are extracted using a proposed model that builds on Painter-Shenoy network swelling model while taking into account the glass-like characteristic below a critical swelling ratio, which also scales inversely with thickness. (C) 2017 Wiley Periodicals, Inc.