The 3‐dimensional phase diagram in quaternary systems of polymers and solvents

A 3‐dimensional phase diagram based on the equilateral tetrahedron has been developed to aid the visualization of the phase relation in a quaternary, multiphase system involving polymers and solvents. The technique developed is straightforward. It presents a clear picture of the “tie rods” and the “equilibrium surfaces” in a quaternary system as compared to the “tie lines” and “equilibrium curves” in a ternary system. With the aid of this 3‐dimensional phase diagram, one can minimize the experimental effort in establishing the phase relations of a quaternary system.