(264b) Understanding the Impact of Pore-Polymer Interactions on the Mobility of Poly(ethyleneimine) Confined in Mesoporous SBA-15: Quasi-Elastic Neutron Scattering Studies
AIChE Annual Meeting
Tuesday, November 9, 2021 - 8:16am to 8:32am
Herein, we study the impact of the interaction modes between the pore surface and poly(amines) with a model system comprised of branched-poly(ethyleneimine) (BPEI) supported in mesoporous SBA-15 silica. Chain mobilities of BPEI are quantitatively analyzed using quasi-elastic neutron scattering (QENS) in tandem with coarse-grained molecular dynamics (MD) simulations. The pore-polymer interactions are tuned by grafting organosilanes having different end groups to the silica surface, leading to different levels of attraction between BPEI and the pore walls of silica. Chain mobilities of BPEI undergoing four different interaction modes with pore walls are investigated. The first mode brings covalent tethering of amine sites of BPEI to pore surface via halide-amine reaction, where alkyl halides are grafted onto pore surfaces. The second interaction is acid-base and hydrogen bonding interactions based on silanols decorating the native SBA-15 silica, which strongly interact with amine groups of BPEI. The third interaction considers relatively weak interaction with pore surface and BPEI by substituting acidic silanols into basic aminoalkyl groups on the pore walls, so that pore walls interact with BPEI mainly by inter-amino hydrogen bonding. Lastly, repulsive, van der Waals interaction (via grafting aliphatic chains on pore walls) yields the weakest interaction between pore walls and BPEI. QENS (High-Flux Backscattering Spectrometer; HFBS at NIST) and MD simulation revealed that the chain mobilities of BPEI are significantly influenced by different surface groups appearing on the pore walls. The strong/transient interaction (acid-base, hydrogen bonding) due to silanol-BPEI interaction yielded the slowest motions, covalent bonding and repulsive interactions resulted in slightly increased mobility, and hydrogen bonding (aminoalkyl-BPEI; without acid-base interaction) brought significantly recovered mobility as compared to bulk PEI. We hypothesize that PEIâs mobility depends not only on the attraction level with the pore walls but also on its chain conformation in the presence of surface capping groups on the pore walls. To understand further, these results are currently being coupled with additional QENS experiments, alongside insights developed via other techniques.
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