(122b) Continuous Synthesis and in Situ SAXS Analysis of Silica Nanoparticles in Liquid Phase

Manuel Meier, Julian Ungerer, Hermann Nirschl

Karlsruhe Institute of Technology, Institute for Mechanical Process Engineering and Mechanics, Karlsruhe, Germany

E-Mail: manuel.meier@kit.edu

Abstract

The synthesis of specific nanomaterials with defined properties (size distribution, morphology etc.) requires detailed knowledge about the particle formation and growth mechanisms. To gain knowledge about the relevant mechanisms, the use of time-resolved particle characterization techniques is helpful. In our previous work, we have developed a laboratory-scaled small angle X-ray scattering (SAXS) device providing time-resolved information on silica particles synthesized in liquid phase [1, 2]. The synthesis was conducted by means of a semi-batch reactor, i.e., samples were analysed ex situ by means of SAXS. The obtained results were in a good agreement with results published by others, e.g. Boukari et al. [3], Keefer and Schaefer [4] and Jelinek [5], indicating a gradual densification process dependent on reaction progress. In addition, the porosity of Stöber particles depends on the growth rate that in turn is affected by the reaction conditions: While low growth rates lead to compact structures, high growth rates result in particles with enlarged surfaces.

However, ex situ analyses often lead to unavoidable side effects due to the abrupt change of the ambient conditions of the sample under study, especially for the first minutes. To minimize such errors, the experimental setup was modified in such a way that in situ SAXS analyses can be conducted. The modification is based on a laminar flow reactor, which is directly connected to the SAXS device. The reaction time can be varied by a change of the flow rate of the reactants or the reactor length. For validation, compact silica nanoparticles were synthesized via a modified Stöber process [6] and analysed in situ by SAXS. Hereinafter, the obtained results are used to gain new knowledge about the gradual densification process and therefore a deeper understanding how to synthesize microporous silica particles.

Some practical drawbacks had to be overcome in order to ensure proper mixing of the reactants as well as to control properly the reaction temperature. Using the optimized setup, the reaction conditions were varied systematically and the particles were characterized by the in situ SAXS technique. In this contribution the optimized experimental setup as well as new insides about the particle formation process of silica nanoparticles will be presented in detail.

References

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2. Gutsche, A., et al., Time-resolved SAXS characterization of the shell growth of silica-coated magnetite nanocomposites. Journal of Nanoparticle Research, 2014. 16(7).

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6. Stöber, W., A. Fink, and E. Bohn, Controlled growth of monodisperse silica spheres in the micron size range. Journal of Colloid and Interface Science, 1968. 26(1): p. 62-69.