Fractal crystal growth of poly(ethylene oxide) crystals from its amorphous monolayers

The fractal crystal growth process of the PEO monolayer with a molecular weight (M¯w≈2.0×106g/mol) and a distribution (M¯w/M¯n=4.24) has been followed on the substrate of the silicon wafer using AFM equipped with a hot stage. A depletion zone between the ramified crystals and the viscous amorphous layer was found in the AFM height images. The formation of the depletion zone shows that the molecules have to “break up” with the amorphous layer and then diffuse through the depletion zone to join the crystals. The diffusion process further means the diffusion-controlled mechanism resulting in the fractal crystal pattern with a fractal dimension Df ≈ 1.63. The linear feature of the crystal pattern radius growth with time means that the surface kinetic process plays a key role in the crystal growth.