Synthesis of nano-SiO₂@PTPEG-VPA copolymer and its effects on early-age cement hydration

Incorporating nano-SiO₂ particles into cement paste has garnered significant attention for enhancing the performance of hardened cement paste. However, the agglomeration of nanoparticles in the pore solution of cement-water system poses a challenge for cost-effective and efficient applications. Meanwhile, superplasticizers containing phosphate groups exhibit strong complexation with calcium ions and show promise in improving the dispersion performance. This study introduces a surface chemical modification technique to enhance the dispersibility of nano-SiO₂. Firstly, poly(isoprenyl oxy poly(ethylene glycol) ether-random-vinylphosphonic acid) (PTPEG-VPA), a silanized superplasticizer containing phosphate moieties, is copolymerized and chemically grafted onto pristine nano-SiO₂ surfaces through condensation and silanization processes. The resulting core-shell SiO₂@PTPEG-VPA nanoparticles are comprehensively characterized using FT-IR spectroscopy, TGA, DLS, TEM, BET surface area analysis, and zeta potential measurements. The results indicate that introducing phosphate moieties improves the dispersion capacity of grafted copolymers, thereby reducing the severe agglomeration of nano-SiO₂ in solution. Subsequently, the impact of SiO₂@PTPEG-VPA on cement hydration and early-age strength development is investigated using microcalorimetry and TGA characterization. Finally, a mechanism is proposed to explain the observed retarding effects of grafted PTPEG-VPA on pristine SiO₂. Overall, this study provides novel insights into the chemical design of nanoparticles, aimed at manipulating cement paste properties.