Fig. 2: Quantitative analysis of surface stress driven a-PP phase separation.

a–g AFM images across the compressive surface of PP cantilever after 4 h of 95 °C oven heat. All images have the same scale bars. h Surface stress (blue line), a-PP droplet average height (pink line), and a-PP droplet volume per unit (red line) area across the compressive surface of PP cantilever after 4 h of 95 °C oven heat, respectively. i The normalized volumetric flow \(\hat{{{{\bf{v}}}}}\) of a-PP under different surface stress conditions and for oven temperatures of 60–95 °C, respectively. The linear fitting is consistent with the a-PP behaving like a Bingham plastic fluid. j The yield stress σ_y to initiate a-PP flow to the surface of bulk PP sheet under conditions of 60 to 95 °C oven heat, calculated from the intercepts of normalized volumetric flow, \(\hat{{{{\bf{v}}}}}=0\) in Fig. 2i. k Arrhenius plot of Eq. (2) at compressive surface stress conditions of −15 (pink line) to −26 MPa (red line). Data extracted from 5 temperatures in Fig. 2i (green dash line). The slope of linear fit at each stress is the flow activation energy. l The flow activation energy obtained from 5-temperature fit (Fig. 2k) and 3-temperature fit (Suppl. Fig. 13). Error bars indicate standard deviation. Source data are provided as a Source Data file.