Structural Evolution of Aqueous Zirconium Acetate by Time-Resolved SAXS and Rheology. Yunjie Xu

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1 Structural Evolution of Aqueous Zirconium Acetate by Time-Resolved SAXS and Rheology Yunjie Xu 1

2 Outline 1.Experiment Methods -Chemical synthesis -SAXS measurement 2. SAXS Modeling 3. Results 4. Conclusions

3 Research Purpose The transformation from the complex species in solution to solid particles is a complicated process and requires insight into solution chemistry, coordination chemistry, polymerization, and nucleation. Detailed studies of the transformation require non-invasive techniques, which can access the early stages of the transformation.

4 Experimental Methods The structural evolution at concentrations of 22, 43 and 220 mm was furthermore investigated by time-resolved SAXS at a moderate temperature of 85 C wt% Zr (2.2 M) (Sigma-Aldrich , density g ml-1) was used as received and was diluted by a factor of 5, 10, 25, 50 and 100 resulting in Zr concentrations of 0.44, 0.22, 0.087, 0.044, M. NaCl (Fluka 71379) was dissolved in deionized water to a stock solution of 1.0 M, which was mixed with water and zirconium acetate to prepare five solutions with a fixed Zr(ac)4 concentration of M and NaCl concentrations of 0.20, 0.30, 0.40, 0.50 and 0.60 M. SAXS measurements were performed on a modified Bruker AXS NanoSTAR SAXS camera with a three pinhole collimated beam and a rotating copper anode X-ray generator.

5 SAXS Modeling

6 SAXS data, I(q)/C, for zirconium acetate samples with concentrations of 22 and 87 mm aged at 85 oc for 24 h and as a reference the data for untreated samples as shown as well

The aggregation of the chains of organometallic complexes are in general prevented by an electrostatic interaction potential and upon even subtle heating the stabilization is not sufficient and the

7 The aggregation of the chains of organometallic complexes are in general prevented by an electrostatic interaction potential and upon even subtle heating the stabilization is not sufficient and the chains may grow to significant lengths without aggregation, i.e. the complexes still display significant electrostatic repulsion. The interaction potential is assumed to be dominated by the electrostatic repulsion and the attractive van der Waals as described by the classical DLVO theory. (A) Photograph of five vials with a concentration of 87 mm Zr(Ac)4 and increasing concentration NaCl from 200 to 600 mm taken after aging for 10 days at room temperature. (B) SAXS of samples right after addition of NaCl to give concentrations of 200, 400 and 600 mm and fitted to the PRISM model. (C) Same samples measured after ageing for 10 days.

8 Time-resolved SAXS and rheology measurements 87mM and 220mM concentrations an increase in slope is observed, the onset of which was reproduced in more than three experiments. This increase in slope can be interpreted as the point at which the polymer gel extends throughout the volume of the sample container The complex viscosity, η*, during aging at 85 oc for concentrations of 43, 87 and 220 mm. The inset show the first 30 min to highlights the slope increase at t = 10 min for the sample with a concentration of 220 mm

9 Time-resolved SAXS data for 220 mm zirconium acetate aqueous solution measured for 22.5 h at 85 oc The SAXS invariant for the series are approximately constant showing that the amount of material and the scattering contrast are unchanged throughout. Selected parameters from the PRISM modeling of zirconium acetate solution. (A) Chain radius, R. (B) Chain length, L. (C) The correlation radius, Rc (fixed to 160 Å for 22 mm). (D) Cluster Scale (Rg = 100 Å)

10 Comparison of the evolution of the complex viscosity and the cluster scale for 220 mm zirconium acetate aqueous solution at 85 oc.

11 Conclusion These linear oligomer species are electrostatically stabilized and their behavior can be explained by the classical DVLO theory. A model expression for the SAXS intensity based on the Polymer Reference Interaction Site Model (PRISM) was found to describe the system very accurately and allowed a detailed modeling of the time-resolved SAXS data collected at 85C as the polymeric chains grow and form a hydrogel. Aggregation occurs simultaneously with chain growth. Except for the lowest concentrations, where no gelling occurs, it was found that the increase in viscosity followed the increase in the degree of aggregation of the polymers

12 Acknowledgement Dr. Carlo Segre Dr. Adam Hock Everyone in my group Everyone in Phy570 class

13 Thank you!

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