Universal Aspects of Macromolecules in Polymer Blends, Solutions, and Supercritical Mixtures

?We demonstrate that macromolecules in miscible polymer blends may behave as poor, theta and good polymeric solvents for each other. We construct a conceptual phase diagram, indicating the range of validity of the random phase approximation, outside of which molecules contract or expand beyond their unperturbed dimensions, contrary to common assumptions. Similarly, the concentration fluctuation correlation length collapses onto a master curve for polymeric, liquid and supercritical solvents, indicating that macromolecules behave universally in these media over a wide range of thermodynamic variables.