In situ small-angle X-ray scattering studies during the formation of polymer/silica nanocomposite particles in aqueous solution. Issue 42 (20th October 2021)

• Record Type: Journal Article
• Authors: Czajka, A.; Liao, G.; Mykhaylyk, O. O.; Armes, S. P.
• Is Part Of: Chemical science. Volume 12:Issue 42(2021)
• Page Start: 14288
• Page End: 14300
• Publication Date: 2021-10-20
• Subjects: Chemistry -- Periodicals; 540.5
• DOI: 10.1039/d1sc03353k
• Languages: English
• ISSNs: 2041-6520

Abstract

Abstract : SAXS is used to study the formation of polymer/silica nanocomposite particles prepared by surfactant-free aqueous emulsion polymerization of 2, 2, 2-trifluoroethyl methacrylate in the presence of silica nanoparticles using a azo initiator at 60 °C. Abstract : This study is focused on the formation of polymer/silica nanocomposite particles prepared by the surfactant-free aqueous emulsion polymerization of 2, 2, 2-trifluoroethyl methacrylate (TFEMA) in the presence of 19 nm glycerol-functionalized aqueous silica nanoparticles using a cationic azo initiator at 60 °C. The TFEMA polymerization kinetics are monitored using 1 H NMR spectroscopy, while postmortem TEM analysis confirms that the final nanocomposite particles possess a well-defined core–shell morphology. Time-resolved small-angle X-ray scattering (SAXS) is used in conjunction with a stirrable reaction cell to monitor the evolution of the nanocomposite particle diameter, mean silica shell thickness, mean number of silica nanoparticles within the shell, silica aggregation efficiency and packing density during the TFEMA polymerization. Nucleation occurs after 10–15 min and the nascent particles quickly become swollen with TFEMA monomer, which leads to a relatively fast rate of polymerization. Additional surface area is created as these initial particles grow and anionic silica nanoparticles adsorb at the particle surface to maintain a relatively high surface coverage and hence ensure colloidal stability. At high TFEMA conversion, a contiguous silica shell is formed and essentially no further adsorption of silica nanoparticles occurs. A population balance model is introduced into the SAXS model to account for the gradual incorporation of the silica nanoparticles within the nanocomposite particles. The final PTFEMA/silica nanocomposite particles are obtained at 96% TFEMA conversion after 140 min, have a volume-average diameter of 216 ± 9 nm and contain approximately 274 silica nanoparticles within their outer shells; a silica aggregation efficiency of 75% can be achieved for such formulations.