## 3 Results
The thickness of the shells surrounding the emulsion-derived core-shells was found to be relatively uniform at \(\sim\) 600 nm for several batches of products all synthesized using the identical synthesis method described in the experimental methods section (Figure 4B). The polymorph phase of the CaCO\({}_{3}\) shell appears to depend on the conditions used during precipitation. As presented in Figure 5, an initial ratio of 2.5:1 Mg\({}^{2+}\)/Ca\({}^{2+}\) in the mother solution yielded crystalline shells, but an initial ratio of 5:1 Mg\({}^{2+}\)/Ca\({}^{2+}\) yielded an apparently amorphous mineral shell, even after gentle heating at 50 \({}^{\circ}\)C for 24 h.  
Figure 4: Scanning electron microscopy (SEM) images of intact and intentionally fractured CaCO\({}_{3}\)-coated emulsion microcapsules. (**A**) The core-shell microcapsules consist of a smooth and continuous crystalline CaCO\({}_{3}\) coating. (**B**) Intentionally fractured microcapsules show a relatively thick continuous shell with a hollow interior where the liquid resided. The shell thickness was consistently \(\sim\)500 nm using this procedure. Figure 3: Scanning electron microscopy (SEM) images of the core-shell microcapsules. (**A**) Core-shell microcapsules with oil interior created by coating oil-in-water emulsion droplets with CaCO\({}_{3}\) using the PILP process. Their diameters range from 2 to 4 μm in this batch. (**B**) Core-shell microcapsules with aqueous interior created by coating liposome vesicles with CaCO\({}_{3}\) using the PILP process. Their diameters are distributed below 2 μm. Both emulsion and liposome-derived microcapsules are slightly larger than the emulsion droplets and liposomes alone due to the \(\sim\)500 nm thickness of the applied mineral coating. The amorphous core-shell microcapsules were smaller in size (2-3 \(\upmu\)m) than the crystalline microcapsules (2-10 \(\upmu\)m), which is presumably due to a difference in stability between the stabilized droplets, where the liposome system yields smaller metastable droplets as a template solid mineral shell deposition. These liposome-based microcapsules were not fractured as the larger emulsion-based microcapsules were due to their very small size. The thickness of the shell and the size of the liquid interior may be observed from the confocal micrograph shown in Figure 5.  
Mineral phase identification of the CaCO\({}_{3}\)-coating on liposome-derived microcapsules created using the 2.5:1 Mg\({}^{2+}\)/Ca\({}^{2+}\) ratio was carried out using powder XRD (Figure 6). The pattern contains diffraction peaks that are consistent with the Joint Committee on Powder Diffraction Standards (JCPDS) standard for calcite, with some peak shifts caused by lattice strain from the incorporation of Mg into the lattice, which results in slightly smaller characteristic d-spacings. The results are consistent with the Mg\({}^{2+}\) incorporation behavior found in calcium carbonate films generated by the PILP process under similar Mg\({}^{2+}\)/Ca\({}^{2+}\) ratios [39]. The absence of the characteristic signal of vaterite at 20 of 25.0\({}^{\circ}\) and of aragonite at 45.9\({}^{\circ}\) suggest that neither of these phases is present in any significant amount. These characteristic peaks are indicative of polymorph presence and are used specifically to quantify the polymorph distribution in calcium carbonate samples [44]. Figure 5: Tailoring the crystallinity of the microcapsules. The images on the left are optical micrographs, while the images on the right are using polarized light. (**A**,**B**) Microcapsules generated using a 2.5:1 ratio of Ca/Mg display birefringence, indicating crystallinity. (**C**,**D**) Microcapsules generated using a 5:1 Mg/Ca ratio lack birefringence, indicating that the mineral remains amorphous under these conditions. A gypsum waveplate was used for image B, giving a magenta (1 st-order red) background, because the amorphous particles lack birefringence and are, therefore, difficult to see under crossed-polars.