Density, Elastic Constants, and Thermal Conductivity of Interfacially Polymerized Polyamide Films for Reverse Osmosis Membranes

The thickness, volumetric mass density, longitudinal elastic constant, and thermal conductivity of fully aromatic polyamide reverse osmosis membrane active layers synthesized by interfacial polymerization were measured using a combination of Rutherford backscattering spectrometry, quartz crystal microbalance measurements of areal mass density, optical ellipsometry, atomic force microscopy, picosecond acoustics, and time-domain thermoreflectance (TDTR). A support-free synthesis approach was used to produce smooth three-dimensionally cross-linked polyamide films from m-phenylenediamine (MPD) and trimesoyl chloride (TMC) at a fixed molar ratio of 99:1 MPD:TMC with 0.1-2 wt % MPC and 0.005-0.1 wt % TMC. A novel method to measure the areal mass density of nanoscale polymer films by Rutherford backscattering spectrometry was developed to aid in characterization of the volumetric mass density of the membranes. The volumetric mass density and longitudinal elastic constant of free-standing polyamide films increase monotonically as the concentration of monomers used to synthesize the films increases. The small thermal conductance of the interfaces prevents direct measurement of the thermal conductivity of the free-standing films; however, based on the assumption of constant interface conductance and thermal conductivity, the thermal conductivity is 0.30 ± 0.06 W m^-1 K^-1.