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Figure 6
Effect of PSS and CaCl2 concentrations. CXDI images obtained on microparticles after long reaction times (≥24 h) for different initial concentrations of PSS (vertical axis) and CaCl2 (horizontal axis). (a) 8 mM 1.94 g l−1 24 h (Vx = 13.8 nm) with (i) a 2D view and (ii) a 3D view. The shell (white) was cut into two parts to reveal its smooth inner part. The core is blue. (b) 8 mM 1.0 g l−1 24 h (Vx = 16.4 nm) with (i) a 2D view and (ii) a 3D view of half the microspheroid. In inset (iii), a vaterite crystal (orange) extracted from the outer part of the shell is shown and compared with a truncated hexagonal base bipyramid. Detailed results are shown in Figs. 1[link](e) and 1[link](f). The same kind of segmentation can be seen in the insets of (c), (e) and (f). (c) 8 mM 0.27 g l−1 24 h (Vx = 12.6 nm) with (i) a 2D view, (ii) a 3D view of half of the microspheroid, (iii) a 2D view of a selected region and (iv) a 3D view revealing the nanostructure of the pole. The color corresponds to the distance of the surface to the center of the microspheroid. This allows us to highlight the spheroidal shape of the microparticles. A zoomed-in view at the pole allows us to identify the presence of individual nanoparticles of ∼30 nm. In (iii), the image is obtained by superimposing a stack of images oriented according to z and over a thickness of 400 nm. In each pixel of the resulting image, the grayscale is equal to the maximum grayscale of the pixels in the image stack (details in Fig. S12). (d) 30 mM 8.0 g l−1 72 h (Vx = 17.7 nm) with (i) a 2D view and (ii) a zoomed-in view of the white rectangular region. The thickness of the shell is difficult to observe and close to 40 nm. (e) 30 mM 1.0 g l−1 72 h (Vx = 17.7 nm) with (i) a 2D view and (ii) a 3D view. The shell (white) was cut into two parts to reveal the inner part of the shell. The core is blue. (f) 30 mM 0.27 g l−1 24 h (Vx = 32.7 nm) with (i) a 2D view and (ii) 3D views of the largest crystal of vaterite extracted from the outer part of the shell. In (i) the shell cannot be seen. Vx = voxel size. The dotted rectangular line represents the region of the inner part of the shell.

IUCrJ
Volume 9| Part 5| September 2022| Pages 580-593
ISSN: 2052-2525
https://doi.org/10.1107/S2052252522006108