Design Strategies for Length Control of Colloidomer Chains by Magnetic Alignment

Colloidal freely-jointed chains made of DNA-functionalized emulsion droplets can serve as a model system for the study of polymer dynamics or the design of emulsion gels. Here we show the length and composition of droplet chains can be controlled using magnetic alignment. We immerse oil droplets in an aqueous ferrofluid, trigger their chaining with magnetic fields, and we record the growth and size distribution of the resulting chains over time. Increasing the ferrofluid concentration limits droplet motion to the direction of the magnetic field, favoring the formation of single-file chains over lateral clustering. In addition, we show that introducing inert droplets results in chain splitting, which shortens and narrows the chain length distribution. This method allows us to gain better control of the folding of short chains into rigid foldamers via preprogrammed DNA interactions. Alternatively, these short chains can be cross-linked by rotating the magnetic field resulting in networks whose mesh size is controlled by the initial length distribution, resembling spiderwebs. This level of control opens the path to designer emulsions expecting novel rheological properties.