Stabilization of Miniemulsion Droplets by Cerium Oxide Nanoparticles: A Step toward the Elaboration of Armored Composite Latexes

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• 作者：Nancy Zgheib ; Jean-Luc Putaux ; Antoine Thill ; Franck D鈥橝gosto ; Muriel Lansalot ; Elodie Bourgeat-Lami
• 刊名：Langmuir
• 出版年：2012
• 出版时间：April 10, 2012
• 年：2012
• 卷：28
• 期：14
• 页码：6163-6174
• 全文大小：623K
• 年卷期：v.28,no.14(April 10, 2012)
• ISSN：1520-5827

文摘

Stable methyl methacrylate (MMA) miniemulsions were successfully prepared using for the first time cerium oxide (CeO₂) nanoparticles as solid stabilizers in the absence of any molecular surfactant. The interaction between MMA droplets and CeO₂ nanoparticles was induced by the use of methacrylic acid (MAA) as a comonomer. Both MAA and CeO₂ contents played a key role on the diameter and the stability of the droplets formed during the emulsification step. Cryo-transmission electron microscopy (TEM) images of the suspensions formed with 35 wt % of CeO₂ showed the presence of polydisperse 50鈥?50 nm spherical droplets. More surprisingly, some nonspherical (likely discoidal) objects that could be the result of the sonication step were also observed. The subsequent polymerization of these Pickering miniemulsion droplets led to the formation of composite PMMA latex particles armored with CeO₂. In all cases, the conversion was limited to ca. 85%, concomitant with a loss of stability of the latex for CeO₂ contents lower than 35 wt %. This stability issues were likely related to the screening of the cationic charges present on CeO₂ nanoparticles upon polymerization. TEM images showed mostly spherical particles with a diameter ranging from 100 to 400 nm and homogeneously covered with CeO₂. Besides, for particles typically larger than 200 nm, a buckled morphology was observed supporting the presence of residual monomer at the end of the polymerization and consistent with the limited conversion. The versatility of these systems was further demonstrated using 35 wt % of CeO₂ and replacing MMA by n-butyl acrylate (BA) either alone or in combination with MMA. Stable monomer emulsions were always obtained, with the droplet size increasing with the hydrophobicity of the oil phase, pointing out the key influence of the wettability of the solid stabilizer. The polymerization of Pickering miniemulsion stabilized by CeO₂ nanoparticles proved to be an efficient strategy to form armored composite latex particles which may find applications in coating technology.