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DLS and AFM Studies on the Cluster Evolution of Or
DLS and AFM Studies on the Cluster Evolution of Or

DLS and AFM Studies on the Cluster Evolution of Organically Modified Silica Gels Catalyzed by a Super Strong Acid Time evolution of cross-linking clusters prepared by the sol−gel method was investigated by dynamic light scattering (DLS) and atomic force microscopy (AFM). The samples were prepared by the sol−gel synthesis of 1,8-bis(triethoxysilyl)octane (Tes-Oct) in the presence of phosphotungstic acid (PWA) as a super strong acid. The reaction batches were quenched at various reaction times, dtpmp scale inhibitorfollowed by dilution with a large amount of the solvent. DLS and AFM techniques simultaneously revealed that there exists a maximum cluster size, Rh and rAFM, respectively, for a specific PWA concentration. The information on the clusters density, ρcluster = (rAFM/Rh)3, generated during the reaction process was obtained by systematically comparing the DLS data obtained in the swollen state to the AFM data measured in the shrunken state of the cross-linked clusters. It was found that not only the cluster size but also ρcluster exhibited a maximum for [PWA]/[Tes-Oct] = 0.10 near the gel point of the Tes-Oct clusters. Since PWA is not only a super strong acid as a catalyst for the sol−gel synthesis but is also a proton conductor, the resulting materials can be utilized as a fuel-cell membrane. The ac impedance measurements revealed that the proton conductivity also exhibited a similar maximum at this specific PWA concentration, revealing the optimum condition for design of conducting membrane.