Aminopolymer mobility in nano-confined supports with a fluorescent probe

Aminopolymer-mesoporous oxide composites are receiving much attention in the field of direct air CO₂ capture. The low volatility of polymers such as polyethylenimine, combined with the high surface area of the support, make these composites attractive for efficiently capturing CO₂ from dilute streams. Understanding how nanoconfinement in the composite influences polymer segmental mobility, which in turn is coupled with the uptake of CO₂ and diffusion of gas through these composites, will ultimately be critical to the development of more robust and efficient direct air capture systems. Here, we report on the development of a fluorescent probe based on tetrakis(4-hydroxyphenyl)ethylene. The fluorescence intensity of this molecule is strongly dependent on the viscosity of its supporting medium. We demonstrate the probe is a sensitive indicator of polymer T_g and can give additional relative mobility information across wide temperature spans when compared to standard calorimetry measurements. Here, we use the probe to study the effects of polyethyleneimine nanoconfinement in mesoporous silica as a function of pore size, pore functionality, polymer loading, and polymer architecture. Our progress towards the development of an in-operando characterization tool for assessing polymer mobility upon exposure to CO₂, humidity, and other environmental factors will be discussed.