Activity-assisted self-assembly of colloidal particles

We outline a basic strategy of how self-propulsion can be used to improve the yield of a typical colloidal self-assembly process. The success of this approach is predicated on the thoughtful design of the colloidal building block as well as how self-propulsion is endowed to the particle. As long as a set of criteria are satisfied, it is possible to significantly increase the rate of self-assembly, and greatly expand the window in parameter space where self-assembly can occur. In addition, we show that by tuning the relative on-off time of the self-propelling force it is possible to modulate the effective speed of the colloids allowing for further optimization of the self-assembly process.

Figure 1

(a) The colloidal building blocks have been functionalized such that two of the three faces exhibit a short-range attraction. The white arrow indicates the direction of self-propulsion. (b) The target structure to be self-assembled is a hexagonal capsid composed of six colloidal building blocks. (c) Typical disordered aggregate formed when the attraction between colloids is too strong. (d) Percent yield of target structure as a function of the strength of the attractive interaction $\varepsilon$ for passive colloids $(F_a\sigma =0k_{B}T)$.

Figure 2

Percent yield of the target structure as a function of time for binding energy $\varepsilon \approx 11k_{B}T$ and several values of the self-propelling force $F_a$.

Figure 3

Percent yield of the target structure as a function of the binding energy $\varepsilon$ and the self-propelling force $F_a$. The white number at the center of the circle indicates the relative increase in the rate of the assembly process, ${\nu }_{\mathrm{SA}}$, with respect to the best performing passive case that occurs for $\varepsilon \approx 16k_{B}T$.

Figure 4

Antialigned and aligned binding configurations for this choice of colloidal building block. The introduction of self-propulsion stabilized the aligned configuration and destabilized the antialigned configuration.

Figure 5

Percent yield for colloids with a periodic self-propelling force. The self-propelling force $F_a\sigma =25k_{B}T$ is turned on for a time ${\tau }_{\mathrm{on}}$ and then turned off for a time ${\tau }_{\mathrm{off}}$. The interaction energy is fixed at $\varepsilon \approx 16k_{B}T$. The white number at the center of the circle indicates the relative increase in speed of the assembly process ${\nu }_{\mathrm{SA}}$.