Fig. 2. Properties of the PA active layers from IP and SARIP.

a Evolution of S parameters for the PA active layers obtained using IP (blue circles and curve) and SARIP (red circles and curve). Inset: free-volume size distribution of PA active layers derived from the annihilation lifetime distribution of ortho-positronium (o-Ps) with incident energy of 1 keV. b Rejections of uncharged model solutes including raffinose, sucrose, glucose, and glycerol by TFC-PA membrane obtained from IP (blue circles and dashed curve) and SARIP (red circles and dashed curve). Inset: pore size distribution of PA active layers derived from rejection curves of uncharged solutes²⁸. c, d TEM images of the cross-sections of the PA membranes fabricated using IP and SARIP, respectively. The translucent film in each image is the PA active layer and its thickness is analyzed using ImageJ at eight different locations. The reported PA layer thickness represented the average of eight measurements and the error bar represents the standard deviation of eight measurements. e XPS spectra and the corresponding elemental compositions (insets) of PA active layer for TFC-PA membranes fabricated using IP (top) and SARIP (bottom), respectively. The degree of crosslinking (shown in insets) is determined based on the ratio between elements O and N²⁹.