Out of Equilibrium Self-Assembly of Janus Nanoparticles: Steering It from Disordered Amorphous to 2D Patterned Aggregates.

Solvent evaporation driven self-assembly of Janus nanoparticles (J-NPs) has been simulated employing lattice-gas models to investigate the possible emergence of new superlattices. Depending on the chemical nature of NP faces (hence solvophilicity and relative interaction strength), zebra-like or check-like patterns and micellar agglomerates can be obtained. Vesicle-like aggregates can be produced by micelle-based corrals during heterogeneous evaporation. Patterns formed during aggregation appear to be robust against changes in evaporation modality (i.e., spinodal or heterogeneous) or interaction strengths, and they are due to a strictly nanoscopic orientation of single J-NPs in all cases. Due to the latter feature, the aggregate size growth law N(t) ∝ ta has its exponent a markedly depending on the chemical nature of the J-NPs involved in spite of the unvaried growth mechanism. We interpret such a finding as connected to the increasingly stricter orientation pre-requirements for successful (binding) NP landing upon going from isotropic (a ≃ 0.50), to "zebra" (a ≃ 0.38), to "check" (a ≃ 0.23), and finally to "micelle" (a = 0.15-0.17) pattern forming NPs.