The importance of interfacial adhesion in the buckling-based mechanical characterization of materials

The effect of interfacial adhesion on the buckling-based mechanical characterization of materials has been elucidated and practical guides for the correct measurement of the modulus by the buckling method have been given accordingly. When a stiff film on a compliant substrate is compressed, the film buckles into well-ordered sinusoidal surface undulations, over a large area, for the case of good interfacial adhesion and the resulting modulus value agrees well with that observed via the microtensile test. On the other hand, the modulus value obtained from the buckling measurement deviates significantly from that of the microtensile method for the case of poor interfacial adhesion. The nanoscale interface debonds in the poor adhesion case and led to the reduction of effective sample dimension, and this finite width effect has been found to be the reason for the observed discrepancy. Furthermore, simple ways to avoid or reduce the adhesion-related artefacts in the buckling method have been demonstrated. Although the well-known PS/PDMS system has been used in the present work, due to its simplicity to control the interfacial adhesion simply by changing the mixing ratio of PDMS substrate, we believe that the present results should bear the same importance in any other buckling system. Therefore, great care should be taken when one uses or reports the mechanical properties of a material obtained from the buckling method, as well as in studies of physics and mechanics for a given buckling system.