This review offers my personal perspective on the evolution of fluid phase equilibria, traced through the scientific arc of Professor Maurizio Fermeglia. Beginning with classical thermodynamics, his work advanced equations of state and activity-coefficient models, strengthening the thermophysical-property foundations that enable reliable phase-equilibria prediction for complex mixtures and supercritical fluids of industrial relevance. As the limits of purely analytical descriptions became clear, he helped consolidate a molecular viewpoint, using quantum chemistry and molecular simulation to derive physically meaningful parameters and to connect microscopic interactions with macroscopic phase behavior. That vision matured into multiscale molecular engineering, linking quantum and atomistic descriptions to coarse-grained models and process-simulation tools, and enabling predictive design of nanostructured polymers, membranes, and later biomedical systems such as dendrimer-based carriers and protein–ligand complexes. In his final phase, the same “deployable modeling” philosophy expanded to energy and sustainability: process-level simulations and multiscale workflows were coupled to decision-oriented metrics, life-cycle assessment, and circularity considerations, turning impact and boundary conditions into computable design variables. Rather than an exhaustive catalog, this article follows an intellectual arc from classical foundations to simulation-informed thermodynamics, multiscale frameworks, biological translation, and sustainability-by-design, while reflecting on the person who made that trajectory coherent. In honoring Maurizio, I also highlight a standard of practice: rigorous, integrative, and purpose-driven that continues to guide our research*.
