Fig. 2.

Using Janus panels and structured seeds to control polymerization. (A) We control the polymerization sequence using Janus panels. (A, i) Janus panels are constructed from 2 different magnetically patterned layers and spacers, all of which are glued face to face. (A, ii) There are 6 color combinations. Since the 2 faces of the black and green layers are different from each other, Janus panels containing a single black or green magnetically patterned layer have 2 different possible combinations. The Janus panels containing both a green and a black magnetically patterned layer have 4 different possible combinations. Thus, there are 13 possible Janus panels that can be constructed from magnetically patterned layers with the $2\times 2$ dipole array. (A, iii–v) We show 3 different schemes for controlling the polymerization sequence of Janus panels. (A, iii) Blue/red Janus panels self-assemble into dimers at $\mathrm{\Gamma }=3.6g$ and longer polymers at $\mathrm{\Gamma }=2.4g$. (A, iv) Green/black, black/blue, and green/blue Janus panels form dimers at $\mathrm{\Gamma }=6.5g$, trimers at $\mathrm{\Gamma }=3.9g$, and long polymers at $\mathrm{\Gamma }=3.0g$. Interestingly, we find that for the black/blue Janus panel, the black layer interferes with the binding of the blue layer. Therefore, these blue panels can only bind to blue panels from green/blue Janus panels. (A, v) Green/black, black/blue, and green/red Janus panels self-assemble into dimers at $\mathrm{\Gamma }=6.8g$, trimers at $\mathrm{\Gamma }=4.3g$, and hexamers at $\mathrm{\Gamma }=3.0g$. Here, we add 2 extra spacers in the blue/black Janus panel to permit binding of blue panels to one another. (B) We use structured seeds to control polymer topology. (B, i and ii) We use 3- and 4-faced seeds to grow 3-branched (B, i) and 4-branched (B, ii) polymers made of black panels. (B, iii) We use a 3-faced hybrid seed to grow a 3-branched hybrid polymer with 2 green branches and 1 black branch.