Mussel-like Surface Adhesion and Photoinduced Cooperative Deformation of Janus Particles

This study focused on mussel-like surface adhesion and photoinduced cooperative deformation of a unique type of Janus particles (JPs), composed of an isosorbide-based molecular glass bearing push-pull type azo chromophore (IAC-4) and a 2,6-pyridinedicarboxamide-containing poly(dimethylsiloxane) oligomer (H₂pdca-PDMS). The JPs were obtained by the solvent evaporation method in an aqueous medium with the dispersed phase of a solution of IAC-4 and H₂pdca-PDMS in dichloromethane (DCM). The JP formation and its mechanism were investigated by electron microscopy, in situ optical microscopy, and theoretical analysis. The results showed that the Janus structures form through gradual segregation between the two components in the droplets induced by the evaporation of DCM, which follows the ternary phase diagrams calculated according to Flory-Huggins theory. In the following stage, the gradual coalescence of small domains in droplets is controlled by dynamic factors. After being deposited on a substrate, the JPs exhibit unidirectional adhesion with the H₂pdca-PDMS parts spreading on the substrate, while the IAC-4 parts orientate away from the substrate. The mussel-like adhesion is caused by the interfacial interaction of H₂pdca-PDMS with the hard surfaces (i.e., glass and silicon substrates) and its strong ability to spread and wet the surfaces to increase the contact area with the surfaces. Upon irradiation with linearly and circularly polarized laser beams at 488 nm, respectively, a series of unique surface morphologies are observed because of the photoinduced deformation of the IAC-4 parts along the electric vibration direction of the polarized light and the cooperative deformation of the H₂pdca-PDMS parts of the JPs. The cooperative deformation reveals the strong interfacial interaction and cohesiveness between the IAC-4 and the H₂pdca-PDMS phases in JPs. No peeling-off from the substrate is observed after the large-scale deformation, which also indicates the strong adhesion of the JPs on the substrate surfaces. This study not only demonstrates the mussel-like adhesion and unique cooperative deformation behavior but also supplies new insights into the interfacial interaction in JPs as well as that with hard surfaces, thus opening a new avenue for surface modification and functionalization.