Supramolecular Janus Nanocylinders: Controlling Their Characteristics by the Self-Assembly Process

Janus NanoRods (JNR) are anisotropic and non-symmetrical colloids with two faces of different chemical composition. They are difficult to prepare because of their nanometric dimensions and strong anisotropy. Recently, a versatile strategy was developed, allowing the formation of JNR relying on the self-assembly in aqueous medium of two polymers end-functionalized with non-symmetrical and complementary hydrogen bonding stickers. However, the supramolecular JNR prepared following this strategy are out-of-equilibrium (frozen) and therefore their characteristics depend on the self-assembly process. The present study elucidates the formation mechanism of the JNR and the parameters of the self-assembly process influencing their characteristics. The polymers are initially dissolved as unimers in DMSO. Dropwise addition of water triggers the rapid assembly of more and more unimers into long nanocylinders that are unable to grow anymore once formed. Consequently, increasing the dropwise addition rate of water hardly impacts the process, whereas lowering the initial polymer concentration in DMSO reduces both the length and proportion of nanocylinders. Increasing temperature during water addition weakens hydrogen bonds, triggering the formation of a mixture of spheres and nanocylinders. Many supramolecular polymer assemblies are frozen in solution and these findings should help understanding how to control their characteristics, allowing to adapt them to a target application.