CO₂-Induced Structural Changes in 2-EEMPA Investigated with Wide Angle X-ray Scattering and Modeling*

Water-lean solvents are being explored for post-combustion carbon dioxide capture, where increases in CO₂ loading often lead to higher polarity and viscosity. The amine-based solvent N-(2-ethoxyethyl)-3-morpholinopropan-1-amine (2-EEMPA) binds CO₂ by forming tetrameric structures. To study how these structures evolve, we used wide-angle X-ray scattering (WAXS) over a range of CO₂ concentrations (0–42 mol%) and temperatures (–17 to 90 °C). Complementary simulations and experiments were used to evaluate cluster dimensions, densities, and spatial correlations. Scattering length densities derived from the data were incorporated into the Teubner–Strey model to analyze phase separation, and structure factor calculations from both WAXS and molecular dynamics were used to characterize local molecular arrangements. The measurements show that as CO₂ content increases, the characteristic length scales and periodicity of the clusters also grow, consistent with simulation results. These structural trends during CO₂ uptake and release provide input for improving solvent models and guiding solvent design.