(471h) Self-Assembling of a Non-Additive Mixture of Patchy Particles with Engineerable Energetic and Entropic Interactions

Preferential attractions between mixture components are usually realized experimentally and modeled computationally by using the effect of hybridizing DNA or DNA-like strands grafted to the components' cores. While these mixtures are of broad interest to create self-assembled nanoparticle (NP) materials, this study focuses on specific mixtures whose NP-NP interactions could be designed to give a positive kind of non-additive mixing, as this is expected to open up access to more complex phases. Some relevant previous studies include those exploring the non-additive mixing Widom-Rowlinson model¹ and the associated liquid-vapor transitions. More recently, the non-additive mixing of nanoparticles of the Kumar-Molinero model² has been found to result in the formation of a variety of novel mesophases, including some phases typically associated with block copolymers. For DNA-functionalized NPs, most of the current additive models in the literature have only been predicted to form a limited number of crystals and quasicrystals. Hence, based on the idea that a positive non-additive mixing effect could lead to nontrivial phase behavior, we explored the phase behavior of spherical nanoparticles with non-additive grafted patches using molecular dynamics. The idea is to mimic the preferential inter-species attractions between hybridizing grafted DNA or DNA-like strands. The positive non-additivity is physically enacted by decorating the NP surfaces with raised patches of different types which have a preferential attraction. By adjusting the patches' energetic and geometric parameters (like number, height, and width), we tune the extent of non-additivity in our system and explore its effects on the proclivity to form different mesophases. For this purpose, we designed an inter-particle potential that is representative of DNA hybridization, and that is non-additive. As a guide to the phase exploration, we calculated the potential of mean force (PMF) of our patch particles and compared it to the PMF of systems in which phases of interest are formed. We observed different mesophases such as lamellar and network phases. Our results also show that the positive non-additive effect alone is not sufficient to lead to the formation of ordered network mesophases. Some typical characteristics of the DNA-like patchy particles, such as directionality in attractive interactions and the symmetry of the particles, may hinder the formation of ordered networks. We also observed that the particles' ability to assemble into ordered network phases depends on the degree of geometric frustration and directionality of NP-NP interactions. Nonetheless, over a broad range of positive non-additivity mesophases with different lamellar morphologies can be readily realized.

¹Widom, B. & Rowlinson, J. S. J. Chern. Phys. 52, 1670-1684 (1970).

²Kumar, A. & Molinero, V. J. Phys. Chem. Lett. 2017, 8, 5053-5058 (2017).