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.