Evidence for Weak First-Order Nature of Lipid Bilayer Phase Transition from the Analysis of Pseudo-Critical Specific Heat

Abstract

The specific heat of aqueous suspension of dipalmitoylphosphatidylcholine obtained by ac calorimetry is analyzed by the least-squares fit under certain assumptions about the functional form for critical phenomena. Based upon the theory on the critical or pseudo-critical behavior, a weak first-order phase transition is proposed from the fact that a most probable solution follows that pseudo-critical behavior takes place, i.e., α=α'=0.5, the temperature difference between the spinodal points is as small as 0.24 K and the thermal hysteresis at the main transition is smaller than 0.2 K.