Diffusion mechanisms of Janus nanoparticles in cross-linked polymer networks

Janus nanoparticles (JNPs), which typically possess two distinct surfaces with differing physicochemical properties, exhibit more complex diffusion behavior than homogeneous nanoparticles due to their inherent asymmetry and anisotropy. A detailed understanding of their diffusion mechanisms is crucial for the rational design of functional nanomaterials such as nanocarriers for drug delivery and nanomachines. In this study, we employed coarse-grained molecular dynamics (CGMD) simulations to investigate the diffusion mechanisms of JNPs within polymer cross-linked networks of varying stiffness. Our simulations reveal that the mean square displacement (MSD) of all JNPs displays a characteristic crossover from short-time ballistic diffusion to long-time normal diffusion. The translational diffusion rates of JNPs decrease with increasing network stiffness. Furthermore, greater asymmetry in the interaction strengths between the two sides of the JNPs and the network enhances anisotropic diffusion. Dynamical heterogeneity of JNPs is further quantified using non-Gaussian parameters and van Hove correlation functions, which reveal various diffusion behaviors of the two JNP sides. Rotational diffusion is suppressed as the disparity in interactions between the two JNP sides and the network increases, while network stiffness regulates rotation depending on interaction strength. Our findings provide valuable insights into the dynamics of nanoparticles at the microscopic scale, offering theoretical guidance for the design of advanced nanomaterials.