Fig 2. Effect of indenter size on the measured Young’s modulus for a PAAm sample.

A thin PAAm sample was indented with beads of 6.47 μm, 15.0 μm or 21.82 μm diameter. Each box represents the distribution of Young’s moduli calculated from 30 indentation curves, taken at 3 different sample positions. A decrease of Young’s modulus is clearly visible when increasing the indenter diameter from 15.0 μm to 21.82 μm, which might be due to the fact that the indentation strain is larger for smaller indenters, resulting in the Hertz model to not be applicable anymore.