Steering Active-Colloid Assembly by Biasing Dissipation

Abstract

Complex nonequilibrium self-assembly enables the formation of materials with specific patterns and functions from the bottom up. How to directionally control the assembly to form the target configuration is a challenge. Here, we propose a dissipation bias principle for targeted assembly, which highlights that controlling the dissipation tendency can play an important role by modulating the frequency and intensity of local rearrangements. Following this principle, one can induce ordered target configurations from disordered structures and also achieve directional selection among multiple assembly pathways. We use the assembly of active colloids as a platform to show our results.

Figures (4)

• Figure 1: (a) The sketch of the model of the active core-corona particles (ACCPs). (b) The typical configuration of the ACCP assembly system with the disordered phase (blue), stripe phase (green), and trimer phase (orange) in the steady states.
• Figure 2: Schematic of the cloning algorithm for dissipation-biased trajectory sampling. A population of $N$ trajectories is propagated in parallel by unbiased MD for a time window $\tau$. At the end of each window, each trajectory is assigned a statistical weight $P_{\alpha}$ determined by the dissipation $\Delta W$ accumulated over $\tau$. The population is then resampled by cloning or pruning trajectories in proportion to $P_{\alpha}$ and the number of clones is $N_c$.
• Figure 3: (a) The temporal emergence of an ordered trimer cluster from a disordered structure is accompanied by a sudden drop in dissipation, highlighted by the grey-shaded region. We show the time series of the yields of the three states together with the active power input. (b) Representative simulation snapshots for different $\alpha$. Middle-left: no control of the dissipation tendency ($\alpha=0$). Upper-right: energy-avoiding pathways ($\alpha=-1$). Lower-right: energy-seeking pathways ($\alpha=1$). Parameters: $v_0=70$ and $k_s=190$. (c) The effective energy profiles along the reaction coordinate $\phi_{\mathrm{tri}}$. Black solid line: no control. Red dashed line: $\alpha=-1$. Blue dotted line: $\alpha=1$.
• Figure 4: (a) Representative snapshots from simulations for different $\alpha$. When there is no control of the dissipation tendency with $\alpha=0$, the system will assemble into both stripe-ordered configurations and trimer-ordered configurations through two different assembly pathways. On the one hand, for $\alpha=-10<0$, the energy-avoiding pathways will be collected. Particles directionally assemble into the trimer state with low dissipation. On the other hand, for $\alpha=10>0$, the energy-seeking path will be collected. Particles assemble into the stripe structure with high dissipation. (b) The time series of $\phi_{\mathrm{str}}$ (green) and $\phi_{\mathrm{tri}}$ (orange) measured along 100 independent trajectories with $\alpha=0$ . Each curve corresponds to one trajectory. The parameters: $v_0=40$ and $k_s=220$.(c) The time series of the yields of the trimer structure (orange) and the stripe structure (green). Values of $\alpha$: $\alpha=10$ (light) and $\alpha=-10$ (dark). The parameters: $v_0=40$ and $k_s=220$. (d)The effective energy profiles of the system over the reaction coordinate $\phi_{str}$. Black solid line: no control. Red dashed line: $\alpha=-10$. Blue dotted line: $\alpha=10$.