(610c) Tailoring Interfacial Properties in Mixed Matrix Membranes Via Supramolecular Interactions

Mixed matrix membranes (MMMs) are highly attractive for gas separation applications since they can integrate superior sieving properties of nano-filler particles and excellent processability of polymer matrix. However, preparation of MMMs with homogeneously dispersed fillers and defect-free interfacial morphology of ideal interphase contact is challenging due to intrinsically different physical and chemical properties of different phases. Here, we report novel nanocomposite membranes with desirable interfacial morphologies tailored by supramolecular interactions between the filler and polymer matrix. Specifically, these new MMMs are prepared from single-walled carbon nanotubes (SWCNTs) and a triptycene-containing polyimide. SWCNTs show ultrahigh transport rates of gas molecules, conferring on SWCNT-based membranes the potential for high gas permeability. The paddle-wheel like triptycene moieties in polymer matrix induce strong π-π supramolecular interactions with the graphene wall of nanotubes, which effectively improves the interfacial contact between phases and assists homogenous dispersion of SWCNTs via nano-confinement effect.

A series of MMMs was prepared using commercial SWCNTs by solution casting method, which were systematically varied in surface functionality of SWCNTs, metal impurities, aspect ratio of nanotubes and filler loading. In all cases, good adhesion between SWCNTs and triptycene-polyimide and homogeneous dispersion of SWCNTs in polymer matrix without aggregation are verified by cross-sectional SEM images. Fluorescence quenching phenomenon provides a direct evidence for the Ï€-Ï€ stacking interaction between SWCNTs and the polyimide. The improved interfacial properties lead to excellent separation performance in these MMMs. For example, a composite membrane with only 2 wt% filler loading showed nearly an order of magnitude increase in gas permeabilities from the pure polymer without sacrificing CO₂/CH₄ and CO₂/N₂ selectivities. The significant improvement in permeability is the synergistic result of improved diffusivity due to the incorporation of SWCNTs and improved interface morphology due to supramolecular interactions between phases. In this talk, the synthesis, fabrication and characterization of these new MMMs will be presented. Detailed discussion will be provided regarding the dependence of gas transport properties on surface functionality, impurities, aspect ratio of nanotubes and filler loading, with a focus on relating microscopic structures with macroscopic transport properties.