Curing dependent spatial heterogeneity of mechanical response in epoxy resins revealed by atomic force microscopy

Bahrami, Amir [UCL] Morelle, Xavier [UCL] Hông Minh, Lê Duy [UCL] Pardoen, Thomas [UCL] Bailly, Christian [UCL] Nysten, Bernard [UCL]

The local mechanical properties of partially cured epoxy resins based on tetraglycidyl methylene dianiline (TGMDA) are proved to be heterogeneous at the nanoscale with the degree of heterogeneity decreasing when the crosslinking density increases. The fully cured resin can be considered homogeneous on both the nano- and macroscale. These conclusions are supported by a comprehensive statistical analysis of AFM-based local mechanical properties measurements, which reveal changes in the modulus distributions from multimodal to monomodal. Furthermore, the histograms of adhesion force and energy dissipation exhibit decreasing fluctuations with increasing degree of curing. The surface topography of all samples is very flat at the nanoscale, which indicates that the observed features are not the result of surface irregularities. The existence of differently cured domains due to local fluctuations in the curing kinetics is proposed as the origin of the observed properties contrast.