Structural changes in precipitated silica induced by external forces

Schneider, G.J.; Göritz, D.

doi:10.1063/1.3389480

Journal Article

PreJuSER-14190

Structural changes in precipitated silica induced by external forces

Schneider, G. J.FZJ* ; Göritz, D.

2011
American Institute of Physics Melville, NY

The journal of chemical physics 132, 154903 (2011) [10.1063/1.3389480]

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Please use a persistent id in citations: http://hdl.handle.net/2128/7281 doi:10.1063/1.3389480

Abstract: The morphology of pure precipitated silica, silica filled in polydimethylsiloxane rubber, and silica filled in styrene butadiene rubber was studied by means of small-angle X-ray scattering experiments. The silica at a length scale of a few nanometers consists of primary particles, which form aggregates, and clusters with aggregates as basic units. It is evidenced that the aggregate branching, represented by the mass fractal dimension, and the aggregate diameter are different if pure silica and silica in rubber are compared. Contrary, the size of the primary particles and their surface are not influenced. It is demonstrated that the change in the aggregate morphology is due to the external mechanical forces appearing during the mixing process. This is achieved by model experiments using a pistil and a mortar and a composite with different silica fractions. By that means, a systematic change in the morphology with grinding time is observed. Then, the experiments on the composite demonstrate that the major contributions to the mass fractal dimensions are due to the external mechanical forces. In order to test reproducibility and universal validity in the case of precipitated silicas, independent experiments on one silica and further silicas are performed. Several important conclusions are obtained from the study. First, it is shown that a comparison of different pure silica samples without knowing their history may be difficult or questionable. Second, it becomes evident that it is not sufficient to provide only a description of the materials, rather than the details of the sample treatment have to be reported. Therefore, solely the characterization of the morphology of the pure silica is not sufficient to be compared to the mechanical properties of the composites.

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Physics, Atomic, Molecular & Chemical

Note: Many thanks to the beamline staff, Sabine Cunis, Stephan V. Roth, and Rainer Gehrke (BW4 HASYLAB/DESY, Germany), for help and technical assistance. The financial support of the experiments by the HASYLAB/DESY is gratefully acknowledged.

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Appears in the scientific report 2011

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