Global phase diagrams in a polymer-solvent system under the positive and negative pressure at and near the mathematical double points

Global phase diagrams are one of the crucial tools to investigate the phase behavior of simple and complex mixtures both theoretically and experimentally. The critical lines and global phase behavior of polymer-solvent systems under the negative pressure at and near the mathematical double points (MDPs) are studied. We present the critical lines of polymer mixtures in three different planes for various values of interaction energy parameters, and change the factor ( r ) and the deviation coefficient ( Δ ) from the MDPs. We use the full Tompa model to obtain the equation for the critical line within the molecular-field approximation. We find that r and Δ values influence the critical lines and global phase behavior of the system. Moreover, as the r increases, the MDPs shift to the low-pressure region and it will be located in a negative pressure region for r≥9.