Synthesis of Branched Polymers and Dispersion of Nanosilica and the Effect of Their Interaction on Hydrated Cement Morphology

Hypothesis: Dispersion and stabilization of silica nanoparticles are novel approach in the synthesis of hybrid materials in interacting with cement particles. Branched polymers are able to enhance the dispersion and stability of these nanoparticles. Dispersed nanosilica and branched polymers have direct effects on the microstructure of cement. These materials have wide applications in concrete technology. Methods: Various branched polymers were synthesized through in situ radical polymerization of acrylic acid, maleic anhydride and polyethylene glycol methyl ether methacrylate (Mn=950 g/mol) in presence of nanosilica with different contents.
Findings: The molecular structures of the synthesized branched polymers were characterized by Fourier transform infrared spectroscopy (FTIR), proton nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) methods. Thermogravimetric analysis was used to identify the nature of interactions between the branched polymers and nanoparticles. The dispersion state of nanosilica particles within branched polymer solution was studied by dynamic light scattering (DLS) and scanning electron microscopy (SEM) analysis. The results showed a low dispersion in acidic conditions due to agglomeration of nanosilica in the cement. Furthermore, after 30 min sonication, in a neutralized condition, the nanoparticles were dispersed well. In addition, the dispersibility of nanosilica dropped with increases in nanosilica loading. The SEM images showed good dispersion of nanoparticles in the cement medium. It was also demonstrated that the branched polymer had a great influence on the morphology of crystal structure formation in the hydrated cement. The SEM images revealed the best distribution of nanoparticles with 4.7 weight percent nanosilica in the presence of neutralized branching polymers under sonication. From the EDAX results it was also found that the nanosilica particles and branched polymers were dispersed well in the cement medium.