Using a Membrane to Impose Curvature and Alter the Morphologies of Growing Crystal

Current understanding of two-dimensional crystal growth focuses on the interactions between flat substrates and flat growing crystals. By contrast, the understanding of the growth of curved crystals, especially those of non-zero Gaussian curvature of which limited examples exist, considers the stresses imposed by a curved template on a growing two-dimensional crystal, where molecular or colloidal units add to the growing crystal edges from above. In the current study, we demonstrate that when crystals grow within curved vesicle membranes, forces from the membrane and its bending, acting at the edges of the growing crystal, along with the impact of internal pressure, produce morphologies and scaling that run counter to expectations based on systems without the pulling of a growing crystal at its edges. In vesicle membranes, processing conditions, such as cooling rate and transport considerations cause variations in tension history, producing different interplays between bending energies and line tensions. The overall result, demonstrated in quantitative experiments and supported by modeling, is that flat compact solid domains grow reproducibly in small vesicles. However, despite more gradual curvature but higher membrane tension on larger vesicles, flower shaped domains are found and their shapes exhibit increasing complexity with increased vesicles size, tension and, ultimately, bending energy.