Abstract: A novel phenomena or surface microstructure formation mechanism was found during fabricating superhydrophobic polymer films by replica-molding method using porous spherical CaCO3 particle layers as templates. Briefly, polystyrene sulfonate (PSS) doped porous spherical CaCO3 particle suspension was first cast onto a glass substrate and dried towards forming a thin layer of particles. Then low-density polyethylene (LDPE) pellets were bestrewed onto such a CaCO3 particle layer. After the LDPE was heated to melt status (180 oC), another piece of glass plate that had been pre-heated was covered on the LDPE melt for 10 min and then clamped together (3.5 kPa) with the glass substrate bearing the CaCO3 particle layer. After being cooled, peeled off from the glass substrate and rinsed with flowing water, the LDPE surface enwrapping porous spherical CaCO3 particles was obtained. Then it was further etched in 20 wt% HCl solution for 10 min. After washing and drying, the LDPE film with superhydrophobic surface was created, with water contact angle up to (152.8±2.5)o and sliding angle about 6o. Moreover, such superhydrophobicity was confirmed stable to continuous 30 μL water droplets free falling from 100 cm height. SEM imaging showed that completely different with honeycomb structures that were generally formed by using soluble spherical particles as replica templates, conglutinated spherical particles structure were found on the LDPE surface. Moreover, nano structures were also found on each single spherical particle surface. Element characterizations by EDS and XRF both demonstrated that no Ca element existed on or blow herein microstructured LDPE surface. To elucidate the formation mechanism of conglutinated spherical particles structure, the LDPE smooth surface was first covered with sparse porous spherical CaCO3 particles, then heated to melt state and held for 30 min. After being cooled and thoroughly etched with HCl solution, the LDPE surface presented lotus seedpod like structure, e.g., smaller spheres staying within larger holes. Such phenomena demonstrated that it was the spontaneous loading of hydrophobic melt LDPE macromolecules into PSS walled nano pores of CaCO3 particles that formed conglutinated spherical particles structure on LDPE surface. This find not only supplies a new method for fabricating polymer superhydrophobic films but also develops a novel strategy for expanding applications of porous spherical CaCO3 particles.

Key words: spherical CaCO3 particle, polyethylene, replica molding, superhydrophobic, spontaneous loading