Predicting the Geometry of Core–Shell Structures: How a Shape Changes with Constant Added Thickness

Abstract

The core−shell assembly motif is ubiquitous in chemistry. While the most obvious examples are core/shell-type nanoparticles, many other examples exist. The shape of the core/ shell constructs is poorly understood, making it impossible to separate chemical effects from geometric effects. Here, we create a model for the core/shell construct and develop proof for how the eccentricity is expected to change as a function of the shell. We find that the addition of a constant thickness shell always creates a relatively more spherical shape for all shapes covered by our model unless the shape is already spherical or has some underlying radial symmetry. We apply this work to simulated AOT reverse micelles and demonstrate that it is remarkably successful at explaining the observed shapes of the chemical systems. We identify the three specific cases where the model breaks down and how this impacts eccentricity.

Shape of AOT Reverse Micelles: The Mesoscopic Assembly Is More Than the Sum of the Parts

“…Geometry does not completely explain the observed CPE distributions though. In general, across all simulations, there is not a smooth progression from a relatively higher to relatively lower CPE as the surfaces increase, as one would expect if geometry alone explained the data . Instead, for all of the OPLS simulations (OPLS-Std, OPLS-RESP, and OPLS-CM5), we observe a “back-and-forth” behavior where surfaces 1 and 2 have higher CPE, surface 5 has low CPE, and surfaces 3 and 4 oscillate between high and low CPE.…”

“…In our previous work, we built a model that predicts how the CPE of an arbitrary shape changes with added thickness, in the same way the shape is expected to change from surface 1 to surface 5 Figure shows a notable difference in shape between the inner and outer surfaces of the reverse micelle; specifically, surface 5 shows a noticeable drop in both dimensions of CPE.…”