2024 AIChE Annual Meeting
CO2-Modulated Volume Phase Transition in Pnipam Hydrogels
Poly(N-isopropylacrylamide) (pNIPAM) is a well-studied thermoresponsive polymer exhibiting a lower critical solution temperature (LCST) in aqueous solutions or a volume phase transition temperature (VPTT) in crosslinked hydrogels. The volume phase transition is characterized by a transition from a shrunken, hydrophobic state to a swollen, hydrophilic state. For a specific hydrogel composition, this transition is typically modulated by a temperature change. In this study, we conferred CO2 responsivity to pNIPAM hydrogels and show that these gels display a CO2-switchable volume phase transition to enable isothermal and reversible gas-triggered swelling. We systematically measured the effect of hydrogel composition on its VPTT before and after exposure to CO2 using UV-Visible spectroscopy. Over the compositional range presented, we observed shifts of up to 4.2ºC upon CO2 exposure. The reversible nature of the CO2-induced VPTT shift was demonstrated via cyclical addition and removal of CO2, and the morphology throughout this cycle was observed using scanning electron microscopy (SEM). Through analysis of the SEM images, we found that the average pore size of the hydrogels more than doubled after exposure to CO2 and that upon removal of CO2, the pores returned to their initial size. The CO2-responsive system described in this study can be tuned and applied to induce pronounced, isothermal swelling in hydrogels for use in a variety of biomedical applications, including drug delivery and wound dressings.