Fig. 4

Creep compliance measurement on a neat LDPE region of the PS/LDPE sample. The working principle of AFM creep experiment was illustrated in panel a. Initially, the AFM tip was brought into contact with sample surface till it reached the predefined force setpoint. The tip was then held onto the sample for a certain time period, during which the force was kept constant. Following that, the tip was retracted. In the hold segment, the AFM recorded the change in Z motion (panel b). The change in indentation depth as a function of time could be fitted with Voigt version of SLS model using Eq. (13). A representative creep curve was shown in panel c. The black curve was the data, while the red solid line was the fitting curve. The inset indicated the Voigt version of SLS model, featuring a spring (E₁) in series with a spring (E₂)-dashpot (η) Voigt element in parallel