High-performance membranes exceeding the conventional permeability-selectivity upper bound are attractive for advanced gas separations. In the context microporous polymers have gained increasing attention owing to their exceptional permeability, which, however, demonstrate a moderate selectivity unfavorable for separating similarly sized gas mixtures. Here we report an approach to designing polymeric molecular sieve membranes via multi-covalent-crosslinking of blended bromomethyl polymer of intrinsic microporosity and Tröger’s base, enabling simultaneously high permeability and selectivity. Ultra-selective gas separation is achieved via adjusting reaction temperature, reaction time and the oxygen concentration with occurrences of polymer chain scission, rearrangement and thermal oxidative crosslinking reaction. Upon a thermal treatment at 300 °C for 5 h, membranes exhibit an O2/N2, CO2/CH4 and H2/CH4 selectivity as high as 11.1, 154.5 and 813.6, respectively, transcending the state-of-art upper bounds. The design strategy represents a generalizable approach to creating molecular-sieving polymer membranes with enormous potentials for high-performance separation processes.

In this paper, we present a mesoscale simulation method for heavy petroleum combing structural unit (SU) and dissipative particle dynamics (DPD). We proposed 16 basic SUs, which represent the basic structural fragments for heavy petroleum molecules. The SUs were then used as beads in DPD simulation. The process for bead partition and DPD parameter calculation were described. The presented method links the molecular compositional modeling with mesoscale modeling via a chemical-defined mapping process. The equilibrium state of aromatic hydrocarbons with different ring numbers was simulated by the SU−DPD method, proving that the self-assembly behavior of polycyclic aromatic hydrocarbon systems can be properly revealed. On this basis, we built the SU−DPD model for heavy petroleum in terms of averaged four-components molecules. Various heavy petroleum systems were simulated at a coarse-grained level, including pure asphaltene system, asphaltene− toluene system, heavy petroleum system, and heavy petroleum−water system. The simulation results were consistent with the Yen−Mullins model and experimental results.

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Thin silicon dioxide films have been studied as a function of deposition parameters and annealing temperatures. Films were deposited by tetraethoxysilane (TEOS) dual-frequency plasma enhanced chemical vapor deposition with different time interval fractions of high-frequency and low-frequency plasma depositions. The samples were subsequently annealed up to 930 • C to investigate their stress behavior. Films that were deposited in high-frequency dominated plasma were found to have tensile residual stress after annealing at temperatures higher than 800 • C. The residual stress can be controlled to slightly tensile by changing the annealing temperature. High tensile stress was observed during the annealing of high-frequency plasma-deposited films, leading to film cracks that limit the film thickness, as predicted by the strain energy release rate equation. Thick films without cracks were obtained by iterating deposition and annealing to stack multiple layers. A series of wet cleaning experiments were conducted, and we discovered that water absorption in high-frequency plasma-deposited films causes the residual stress to decrease. A ∼40 nm thick low-frequency deposited oxide cap is sufficient to prevent water from diffusing through the film. Large-area free-standing tensile stressed oxide membranes without risk of buckling were successfully fabricated.