From Glycols to Ethers: Hydrogen Bond Donor Character Dictates Ethylammonium Nitrate Mixtures Phase Behavior

Using synchrotron small-angle X-ray scattering/wide-angle X-ray scattering (SAXS/WAXS), density measurements, and molecular dynamics simulations, we examine how ethylammonium nitrate mixes with ethylene glycol, 2-methoxyethanol, and 1,2-dimethoxyethane. These solvents span hydrogen-bond donor ability and polarity, enabling systematic tests of their influence on mixing, nanostructure, and phase behavior. At 25°C, ethylene glycol integrates into the hydrogen-bonded network, preserving the sponge-like polarity-domain pattern and yielding ideal mixing. 2-methoxyethanol induces nanoscale heterogeneity and composition-dependent volumetric asymmetry, evidenced by a subtle low-q excess and a shifted minimum in excess molar volume. In contrast, 1,2-dimethoxyethane weakens ionic connectivity and, when the ionic liquid is the minority component, produces pronounced low-q scattering signaling incipient demixing. Temperature-resolved SAXS of 1,2-dimethoxyethane-rich mixtures shows critical concentration fluctuations near the miscibility gap: forward intensity, correlation length, and scattering invariant rise near the critical temperature. Simulations corroborate nanodomain formation and ether expulsion. Hydrogen-bond donor capacity emerges as a key descriptor linking volumetry, mesoscale organization, and design.