Preparation of Janus-type styrene-acrylic emulsions and performance in polymer cement waterproof coatings

To enhance both the mechanical properties and the waterproofing performance of polymer cement-based waterproof coating. This study modified the surface of nano silica using the silane coupling agent KH570, resulting in modified nano silica (M-SiO 2 ), which was in situ grafted onto the shell layer of a core-shell styrene-acrylate polymer, synthesizing a novel Janus-type styrene-acrylate emulsion (J-SA). The structure and properties of J-SA were characterized using Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and dynamic light scattering. J-SA was then mixed with cementitious material to prepare a waterproof coating, and its performance and mechanism were systematically evaluated through tensile strength, bonding strength, water absorption, contact angle, permeability tests, durability tests, scanning electron microscopy, Brunauer-Emmett-Teller analysis, and atomic force microscopy. The results indicated that the dispersion and stability of J-SA were optimal when the M-SiO 2 content in the shell monomer was 0.8 wt%. The tensile strength and bonding strength of the coating increased by 64 % and 140 %, respectively, while the 7-day water absorption was reduced by 31 %, and the contact angle was 99.16°. The durability of the coating was also optimized. Analysis revealed that the Janus structure effectively addressed the dispersion issue of M-SiO 2 . Furthermore, M-SiO 2 filled the micro-defects within the coating during curing, significantly enhancing the density and nanoscale roughness. These synergistic effects collectively contributed to a significant improvement in the mechanical strength and hydrophobicity of the waterproof coating. This research provides valuable insights into the development of organic-inorganic composite styrene-acrylate emulsions. • The grafting of M-SiO₂ onto the shell structure of core-shell SA forms Janus-type SA emulsions. • Janus-type SA emulsions significantly increase the tensile and bond strength of waterproof coatings. • Janus-type SA emulsions dramatically improve the resistance to UV rays, high temperatures and alkalis. • Waterproof coating internal pore structure has been optimized, the surface of the nano roughness greatly improved.