PXLink: A simulation program of polymer crosslinking to study of polyamide membrane

Crosslinked network polymers have numerous important applications in engineering, biomedicine, and the environment. Establishing a crosslinked polymer network is an essential initial step toward studying the structure and function of polymer membranes. In this study, we developed a Python script named PXLink that integrates with GROMACS software to simulate the crosslinked aromatic polyamide (PA) membrane, which is widely used in desalination and water treatment. PXLink can create chemical bonds between the neighboring carboxyl and amine groups and relax the system during the crosslinking, utilizing energy minimization and molecular dynamics simulations implemented in GROMACS. The accuracy of our protocol has been successfully validated through a benchmark study of water diffusivity and the structural properties of a solvated membrane, including pore size distribution, membrane density, and the stacking of aromatic benzene rings (density profile and ordering). Moreover, the comparison between the dry and wet polymer membranes reveals that the swelling of the membrane surface leads to the expansion of subnanopores and the increased ordering of local structures. After the swelling of the membrane, the number of pores with a radius around the main region of 0.2 nm decreases, while more pores in the range of 0.22–0.38 nm are observed. There is also an increase in the orderliness of local structures, as evidenced by the increasing order parameter of aromatic ring pairs with a distance ranging from 0.7 to 0.8 nm. Our developed script will be a valuable tool for designing and discovering crosslinked polymers.