Densest versus jammed packings of bent-core trimers

Abstract

We identify putatively maximally dense packings of tangent-sphere trimers with fixed bond angles ($\theta = \theta_0$) using a novel method, and contrast them to the disordered jammed states they form under quasistatic and dynamic athermal compression. Incommensurability of $\theta_0$ with 3D close-packing does not by itself inhibit formation of dense 3D crystals; all $\theta_0$ allow formation of crystals with $\phi_{max}(\theta_0) > 0.97\phi_{cp}$. Trimers are always able to arrange into periodic structures composed of close-packed bilayers or trilayers of triangular-lattice planes, separated by ``gap layers'' that accomodate the incommensurability. All systems have $\phi_J$ significantly below the monomeric value, indicating that trimers' quenched bond-length and bond-angle constraints always act to promote jamming. $\phi_J$ varies strongly with $\theta_0$; straight ($\theta_0 = 0$) trimers minimize $\phi_J$ while closed ($\theta_0 = 120^\circ$) trimers maximize it. Marginally jammed states of trimers with lower $\phi_J(\theta_0)$ exhibit quantifiably greater disorder, and the lower $\phi_J$ for small $\theta_0$ is apparently caused by trimers' decreasing effective configurational freedom as they approach linearity.