Thickness-dependent elastic modulus of spin-coated PDMS films

Poly(dimethyl siloxane) (PDMS) elastomer is one of the most commonly used substrate materials for stretchable electronics and artificial skin. Many fundamental studies of soft interface mechanics use PDMS. It is therefore important to understand the factors affecting the mechanical properties of this material. A previous study revealed that the elastic modulus, E, of spin-coated PDMS increased almost three-fold when the PDMS thickness, h, was decreased from 108 to ~30 μm. The enhancement in E had been attributed to the alignment of PDMS chains during spin-coating. In this study, we measured the elastic modulus of spin-coated PDMS with various h from 15 to 110 μm. We found that E increased with decreasing h initially, but on reaching h ~ 20 μm, E decreased with decreasing h. We verified that this phenomenon was universal regardless of the curing condition. We discuss a possible origin for the phenomenon with supporting measurement data.