Statistical Analysis of Peak Force Atomic Force Microscopy Data for the Interphase Thickness and Modulus in Carbon Fiber–Reinforced Epoxy Resin Composites Exposed to Different Heat and Humidity Levels

Heat and moisture influence the interphase properties of polymer matrix composite significantly. The composite samples were exposed to different levels of heat and moisture. The advanced peak force–based quantitative nanomechanics mapping technique with the Derjaguin-Muller-Toropov (DMT) model was used to investigate the interphase at the submicron-scale and nanoscale. The interphase’s width and elastic modulus depend on its location, degree of moisture saturation, the extent of expansion, and shrinkage mechanisms. The interphase’s width is uneven and river-like. The interphase thickness and DMT modulus were collected at ∼15 sites for each condition and ∼15 section lines at each location. The Weibull model linear regression and the moments method with various estimators were employed. Weibull results show that the local moisture content affects the interphase thickness more than elastic modulus. The Weibull analysis shows the enhancement of the interphase thickness from ∼9.5 to 95 nm and reduction of the interphase modulus from ∼22.8 to 19.6 GPa, as the local moisture content reaches ∼95%.