[4] Phase Separation in Pure Component DPPC Lipid Bilayers A lipid bilayer can be treated thermodynamically as a 2D object, and so the work done on the system is no longer W=pdV. The work done on a lipid bilayer is W=dA, where is the surface tension and A is the total area of the bilayer. The fundamental equation for this system is then written as: dU=TdS+dA+dN where N represents the total number of lipid molecules. Notice how has taken the place of P in the usual representation of the internal energy. The pure component DPPC lipid bilayer has a melting temperature of 315K. This melting temperature represents the temperature where a condensed gel phase is in equilibrium with a liquid-crystalline (LC) phase of higher area per molecule. At a temperature below 315K, the bilayer is in a stable equilibrium state as the pure gel phase, and at a temperature above 315K the bilayer is in a stable equilibrium state as a pure LC phase. a.) What are the criteria for phase equilibrium in this system