article published yes Carla Fernández-Rico author 492def71-6250-11f0-b278-d41dbd241b62 Robert W. Style author Stefanie Heyden author Shichen Wang author Peter D. Olmsted author Eric R. Dufresne author Elastic MicroPhase separation (EMPS) provides a simple route to create soft materials with homogeneous microstructures by leveraging the supersaturation of crosslinked polymer networks with liquids. At low supersaturation, network elasticity stabilizes a uniform mixture, but beyond a critical threshold, metastable microphase-separated domains emerge. While previous theories have focused on describing qualitative features about the size and morphology of these domains, they do not make quantitative predictions about EMPS phase diagrams. In this work, we extend Flory–Huggins theory to quantitatively capture EMPS phase diagrams by incorporating strain-stiffening effects. This model requires no fitting parameters and relies solely on independently measured solubility parameters and large-deformation mechanical responses. Our results confirm that strain-stiffening enables metastable microphase separation within the swelling equilibrium state and reveal why the microstructures can range from discrete droplets to bicontinuous networks. This works highlights the critical role of nonlinear elasticity in controlling phase-separated morphologies in polymer gels. https://creativecommons.org/licenses/by-nc-nd/4.0/ Royal Society of Chemistry2026 eng 1744-683X 1744-6848 2506.08958 4140026710.1039/d5sm00594a 222330-342 yes Fernández-Rico, Carla, et al. “Thermodynamics of Microphase Separation in a Swollen, Strain-Stiffening Polymer Network.” <i>Soft Matter</i>, vol. 22, no. 2, Royal Society of Chemistry, 2026, pp. 330–42, doi:<a href="https://doi.org/10.1039/d5sm00594a">10.1039/d5sm00594a</a>. Fernández-Rico, C., Style, R. W., Heyden, S., Wang, S., Olmsted, P. D., &#38; Dufresne, E. R. (2026). Thermodynamics of microphase separation in a swollen, strain-stiffening polymer network. <i>Soft Matter</i>. Royal Society of Chemistry. <a href="https://doi.org/10.1039/d5sm00594a">https://doi.org/10.1039/d5sm00594a</a> Fernández-Rico, Carla, Robert W. Style, Stefanie Heyden, Shichen Wang, Peter D. Olmsted, and Eric R. Dufresne. “Thermodynamics of Microphase Separation in a Swollen, Strain-Stiffening Polymer Network.” <i>Soft Matter</i>. Royal Society of Chemistry, 2026. <a href="https://doi.org/10.1039/d5sm00594a">https://doi.org/10.1039/d5sm00594a</a>. Fernández-Rico C, Style RW, Heyden S, Wang S, Olmsted PD, Dufresne ER. Thermodynamics of microphase separation in a swollen, strain-stiffening polymer network. <i>Soft Matter</i>. 2026;22(2):330-342. doi:<a href="https://doi.org/10.1039/d5sm00594a">10.1039/d5sm00594a</a> C. Fernández-Rico, R.W. Style, S. Heyden, S. Wang, P.D. Olmsted, E.R. Dufresne, Soft Matter 22 (2026) 330–342. Fernández-Rico C, Style RW, Heyden S, Wang S, Olmsted PD, Dufresne ER. 2026. Thermodynamics of microphase separation in a swollen, strain-stiffening polymer network. Soft Matter. 22(2), 330–342. C. Fernández-Rico, R. W. Style, S. Heyden, S. Wang, P. D. Olmsted, and E. R. Dufresne, “Thermodynamics of microphase separation in a swollen, strain-stiffening polymer network,” <i>Soft Matter</i>, vol. 22, no. 2. Royal Society of Chemistry, pp. 330–342, 2026. 222152026-06-30T06:33:11Z2026-07-15T07:42:04Z