A signal of isospin-asymmetric phase transition in the evolution of chemical potential is observed in hot quasi-projectiles produced in the reactions Ca-40,Ca-48 + Al-27 confirming an analogous observation in the lighter quasi-projectiles observed in the reaction Si-28 + Sn-112,Sn-124.(1) With increasing mass, the properties of hot quasi-projectiles become increasingly influenced by secondary emission. Thermodynamical observables exhibit no sensitivity to a different number of missing neutrons in the two reactions Ca-40,Ca-48 + Al-27 and provide a signal of dynamical emission of neutrons, which can be related to a very neutron-rich low-density region (neck) between the projectile and target.