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.