Poly(ethylene oxide) grafted silica nanoparticles: efficient routes of synthesis with associated colloidal stability

In this study, poly(ethylene oxide) monomethyl ether (MPEO) of molecular weight of 5000, 10 000, and 20 000 g mol(-1) were grafted onto colloidal silica nanoparticles (NPs) of a 27.6 nm diameter using two distinct grafting to processes. The first method was based on the coupling reaction of epoxide-end capped MPEO with amine-functionalized silica NPs, while the second method was based on the condensation of triethoxysilane-terminated MPEO onto the unmodified silica NPs. The influence of PEO molecular weight, grafting process and grafting conditions (temperature, reactant concentration, reaction time) on the PEO grafting density was fully investigated. Thermogravimetric analysis (TGA) was used to determine the grafting density which ranged from 0.12 chains per nm(2) using the first approach to 1.02 chains per nm(2) when using the second approach. Si-29 CP/MAS NMR characterization indirectly revealed that above a grafting density value of 0.3 PEO chains per nm(2), a dendri-graft PEO network was built around the silica surface which was composed of PEO chains directly anchored to the silica surface and those grafted to silica NPs by intermediate of >CH-O-Si- bonds. The colloidal stability of the particles during different steps of the grafting process was characterized by small-angle X-ray scattering (SAXS). We have found that the colloidal systems are stable whatever the achieved grafting density due to the strong repulsions between the NPs, with the strength of repulsion increasing with the molecular weight of the grafted MPEO chains.

Automated summary

In this study, different molecular weights of MPEO were grafted onto colloidal silica nanoparticles using two distinct methods, and the influence of PEO molecular weight, grafting process, and conditions on the grafting density was investigated. It was found that a dendri-graft PEO network was formed at a certain grafting density, with PEO chains anchored directly to the silica surface and grafted to silica NPs through intermediates.