小角X射线散射
化学
乳液聚合
肺表面活性物质
聚合
成核
十二烷基硫酸钠
水溶液
散射
动态光散射
分析化学(期刊)
高分子化学
结晶学
化学工程
色谱法
有机化学
聚合物
纳米颗粒
光学
物理
工程类
生物化学
作者
Adam Czajka,Steven P. Armes
摘要
The persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is studied by time-resolved small-angle X-ray scattering (SAXS) at 60 °C using a stirrable reaction cell. TFEMA was preferred to styrene because it offers much greater X-ray scattering contrast relative to water, which is essential for sufficient temporal resolution. The evolution in particle size is monitored by both in situ SAXS and ex situ DLS in the absence or presence of an anionic surfactant (sodium dodecyl sulfate, SDS). Post-mortem SAXS studies confirmed the formation of well-defined spherical latexes, with volume-average diameters of 353 ± 9 nm and 68 ± 4 nm being obtained for the surfactant-free and SDS formulations, respectively. 1H NMR spectroscopy studies of the equivalent laboratory-scale formulations indicated TFEMA conversions of 99% within 80 min and 93% within 60 min for the surfactant-free and SDS formulations, respectively. Comparable polymerization kinetics are observed for the in situ SAXS experiments and the laboratory-scale syntheses, with nucleation occurring after approximately 6 min in each case. After nucleation, scattering patterns are fitted using a hard sphere scattering model to determine the evolution in particle growth for both formulations. Moreover, in situ SAXS enables identification of the three main intervals (I, II, and III) that are observed during aqueous emulsion polymerization in the presence of surfactant. These intervals are consistent with those indicated by solution conductivity and optical microscopy studies. Significant differences between the surfactant-free and SDS formulations are observed, providing useful insights into the mechanism of emulsion polymerization.
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