Photoinduced phase separation and morphology control in amphiphilic dimer melts

We study the phase separation kinetics of a generic amphiphilic dimer melt system using dissipative particle dynamics simulations. Each dimer consists of two incompatible amphiphilic molecule units, A- and B-type, which are connected by a photosensitive covalent bond at their terminal ends. After quenching below the critical temperature, we analyze the model system under alternate light-on and light-off cycles. The photosensitive bond cleaves into two active radicals in the light-on cycle, triggering phase separation. In the light-off state, the radicals reform the covalent bond, which returns the system to a mixed state. This competitive interplay between mixing and demixing drives the formation of a multiscale morphology. This controlled morphological variation has applications in hydrophobic agents, melanin-based material synthesis, and emulsion stabilization. We quantify key structural properties, including the correlation function, structure factor, fractal dimension, interfacial tension, and characteristic length scales. The system exhibits mass fractal characteristics during the off-cycles. The morphologies develop within the bulk, as shown by a static primary peak and an emerging secondary peak in the structure factor. The length scale follows a power-law growth that crosses over from an initial viscous hydrodynamic regime with growth exponent, ϕ≃1, to an inertial hydrodynamic regime, ϕ≃2/3.