Computational study of trimer self-assembly and fluid phase behavior

Abstract

The fluid phase diagram of trimer particles composed of one central attractive bead and two repulsive beads was determined as a function of simple geometric parameters using flat-histogram Monte Carlo methods. A variety of self-assembled structures were obtained including spherical micelle-like clusters, elongated clusters, and densely packed cylinders, depending on both the state conditions and shape of the trimer. Advanced simulation techniques were employed to determine transitions between self-assembled structures and macroscopic phases using thermodynamic and structural definitions. Simple changes in particle geometry yield dramatic changes in phase behavior, ranging from macroscopic fluid phase separation to molecular-scale self-assembly. In special cases, both self-assembled, elongated clusters and bulk fluid phase separation occur simultaneously. Our work suggests that tuning particle shape and interactions can yield superstructures with controlled architecture.

Self-assembly of trimer colloids: effect of shape and interaction range

“…But these trimer shapes did not corresponded to the experimentally synthesized geometry, and the interactions (range of the potential with respect to the particle size) were not similar to experiment. 24 In this work, we simulate shorter interaction ranges (no macroscopic phase separation) 25 than our previous work, 24 which are comparable to the experimental system.…”

“…The size of this bounding cubic box was tuned via 5 % changes every 10 6 trials, in order to obtain an average target number of trimers involved in a pivot, set to N max /5. Note that while the conventional rigid cluster moves implemented in our previous work 24 could not create or destroy clusters due to detailed balance, the GCA does not suffer from this limitation. The algorithm was optimized to minimize the number of pair-wise computations.…”

“…The short range attractive interactions for α = 50 and α = 128 more closely resemble the attractive range of the colloids than the α = 6 case, which was utilized in our previous work. 24 For interactions between attractive, blue beads, the potential cutoff distance, $r_{ij}^c∕\sigma$, was 1.08, 1.2, 3, 3 and 3 for α = 128, 50, 24, 12, and 6, respectively. The rough colloidal beads have less excluded volume overlap, and were therefore modeled as being purely repulsive.…”

“…24 These trials included single trimer translation, rotation, insertion and deletion, smart Monte Carlo, 47 rigid cluster translation and rotations, and parallel configuration swaps. Refer to Ref.…”

FEASST: Free Energy and Advanced Sampling Simulation Toolkit

“…The Free Energy and Advanced Sampling Simulation Toolkit (FEASST) is a free, open-source, modular program to conduct molecular and particle-based simulations with Metropolis, Wang-Landau and Transition-Matrix Monte Carlo methods [1][2][3][4][5][6][7]. FEASST is implemented in C++ and may be imported as a module within Python 2 or 3.…”