In this work, we present pysimm, a python package designed to facilitate structure generation, simulation, and modification of molecular systems. pysimm provides a collection of simulation tools and smooth integration with highly optimized third party software. Abstraction layers enable a standardized methodology to assign various force field models to molecular systems and perform simple simulations. These features have allowed pysimm to aid the rapid development of new applications specifically in the area of amorphous polymer simulations.

•Atomistic simulations can accurately predict and describe several properties of HCPs.•The tunability of HCPs using DVB can be achieved.•Tuning pore size distribution is not sufficient to improve H2/CO2 separation.In this study, we present an atomistic simulation study of several structure-property relationships of hypercrosslinked polymers (HCPs) synthesized using styrene (STR), vinylbenzyl chloride (VBC), and divinylbenzene (DVB). Molecular simulation samples were prepared using a virtual polymerization algorithm, Polymatic, with DVB contents ranging from 0 to 50 mol%. The HCP polymerization algorithm and the models were validated by comparison with experimental data: BET surface area, pore volume, H2 and CO2 loading in 2% DVB samples. Furthermore, the simulated trends in BET surface area and pore volume were in good agreement with the experimental data; both surface areas and pore volumes increased with increased VBC-DVB crosslinking. The same virtual polymerization approach was utilized to study the effect of DVB on the structure and thermodynamic properties of HCPs. Our results demonstrate that DVB mol% significantly altered the structural and gas (H2 and CO2) adsorption properties of the sample. Finally, though our data demonstrated that structural properties can be tuned at the atomistic level by varying the DVB mol%, they did not exhibit a significant improvement in the performance of H2/CO2 gas separation applications.

In this study, we present an atomistic simulation study of several physicochemical properties of polyamide (PA) membranes formed from interfacial polymerization or from a molecular-layer-by-layer (mLbL) on a silicon wafer. These membranes are composed of meta-phenylenediamine (MPD) and benzene-1,3,5-tricarboxylic acid chloride (TMC) for potential reverse osmosis (RO) applications. The mLbL membrane generation procedure and the force field models were validated, by comparison with available experimental data, for hydrated density, membrane swelling, and pore size distributions of PA membranes formed by interfacial polymerization. Physicochemical properties such as density, free volume, thickness, the degree of cross-linking, atomic compositions, and average molecular orientation (which is relevant for the mLbL membranes) are compared for these different processes. The mLbL membranes are investigated systematically with respect to TMC monomer growth rate per substrate surface area, MPD/TMC ratio, and the number of mLbL deposition cycles. Atomistic simulations show that the mLbL deposition generates membranes with a constant film growth if both the TMC monomer growth rate and MPD/TMC monomer ratio are kept constant. The film growth rate increases with TMC monomer growth rate or MPD/TMC ratio. Furthermore, it was found on one hand that the mLbL membrane density and free volume varies significantly with respect to the TMC monomer growth rate, while on the other hand the degree of cross-linking and the atomic composition varies considerably with the MPD/TMC ratio. Additionally, it was found that both TMC and MPD orient at a tilted angle with respect to the substrate surface, where their angular distribution and average angle orientation depend on both the TMC growth rate and the number of deposition cycles. This study illustrates that molecular simulations can play a crucial role in the understanding of structural properties that can empower the design of the next generation RO membranes created from molecular-layer-by-layer (mLbL) on a silicon wafer.