Nonconventional Phases of Colloidal Nanorods with a Soft Corona

Using computer simulations, we investigate the phase behavior of hard-core spherocylinders with a length-to-diameter ratio $L/\sigma =5$ and coated by a soft deformable corona of length $\lambda /\sigma =1.35$. When quasi-two-dimensional layers are formed in smectic and solid phases at low temperatures, the competition between the two intrinsic length scales of the parallel aligned particles leads to the stabilization of different in-plane lattices of nonconventional symmetry, including low-density hexagonal, square, and high-density hexagonal crystals, as well as an intriguing dodecagonal quasicrystal. Our Letter opens up the opportunity to control the assembly of anisotropic nanoparticles into structures with preengineered symmetry-dependent physical properties.

Figure 1

SS-SC potential ${\varphi }_{\mathrm{SS}\text{−}\mathrm{SC}}(r,\mathrm{\Omega })$ as a function of the interparticle minimum distance $d_m$ with $k\sigma =10$ and $\lambda /\sigma =1.35$. Inset: a SS-SC with hard core of length-to-diameter ratio $L/\sigma =5$ and soft corona of thickness $\sim (\lambda -\sigma )/2$.

Figure 2

Left: phase diagram of a system of SS-SCs of shoulder length $\lambda /\sigma =1.35$ in the temperature $T^{*}=k_{B}T/\epsilon$–density ${\rho }^{*}=N{\sigma }^3/V$ plane with $N$ as the number of particles and $V$ as the volume of the system. Labels indicate isotropic $I$ fluids; smectic liquid crystals with (SM) or without (${\mathrm{SM}}^{*}$) overlap between particle coronas; square (SQ), low-density hexagonal (LDH) and high-density hexagonal (HDH) crystals; and dodecagonal quasicrystals (QC12). Gray-shaded areas indicate the coexistence regions. Right: representative simulation snapshots (top view) showing the in-layer arrangement of LDH, SQ, QC12, and HDH phases formed by SS-SCs at $T^{*}=0.12$. The corresponding structure factors and Voronoi tessellations are also included. The coloring scheme of the particles is the same as in Fig. 1.

Figure 3

Two-dimensional (in-layer) pair-correlation function $g_{\perp ,l}(r)$ of SS-SCs as a function of distance $r$ in the SM phases at temperature $T^{*}=0.30$ and varying density ${\rho }^{*}$ as labeled.