Surface stress of isotropic solids under irreversible conditions

Surface stress of isotropic solids is discussed when irreversible mechanisms in the interfacial solid/vapour region occur. When stretching the surface of a sample, even at mechanical equilibrium and in the absence of relaxation, local mobility of atoms and defects can be induced on a thin layer adjacent to the surface. Our thermodynamic formulation takes into account the variation of the surface free energy with the chemical composition of this thin underlayer. Such interfacial region is called non-autonomous phase, as previously designated for fluids by Defay and Prigogine. The theory developed here permits to a new interpretation of the Surface stress. This quantity depends on the variation of the surface free energy with the elastic surface deformation weighted by the relative deformation of the crystal, the aspect ratio of the underlying sheets and the chemical composition. (C) 2003 Published by Editions scientifiques et medicales Elsevier SAS on behalf of Academic des sciences.