Negative heat capacities and first order phase transitions in nuclei and   other mesoscopic systems
  The origin of predicted and observed anomalies in caloric curves of nuclei and other mesoscopic systems is investigated. It is shown that a straightforward thermodynamical treatment of an evaporating liquid drop leads to a backbending in the caloric curve and to negative specific heats in the two phase coexistence region. The cause is found not in the generation of additional surface, but in the progressive reduction of the drop's radius, and surface, with evaporation. 
L. G. Moretto, J. B. Elliott, L. Phair, G. J. Wozniak