Dynamic and reversible self-assembly

While some self-assembled structures must remain stable under changing conditions, the function of many others requires them to undergo adaptive cycles of association and dissociation in response to specific environmental cues. Dynamic behavior is finely controlled in nature - protein channels open and close to send signals along nerves, DNA unwinds to allow replication - yet the design of synthetic systems has mainly focused on controlling the static form rather than the dynamic potential of the final structure. We address this issue in our evaporatively assembled micropost system by combining mesoscale mechanics with the molecular scale chemistry of organic self-assembled monolayers (SAMs). We have shown that modifying the surface chemistry of the posts with different SAMs dramatically affects the stability and reversibility of clusters after the liquid in which they form has evaporated. By using functional groups that interact through a range of van der Waals, hydrogen bonding, or disulfide interactions, and that bear carbon chains of varying lengths, we are able to fine tune the degree of reversibility along the entire spectrum from complete cluster retention to complete disassembly.

By introducing solvents that disrupt the bonding network between posts, we gain responsive, temporal control over disassembly. Combining surface functionalization, solvents, and area-selective microcontact printing enables us to specify arbitrary degrees of spontaneous or environment-induced reversibility with precise temporal and spatial patterning.