The interfacial microstructure of PBs has been investigated extensively using experiments, simulations, and theories in the last decades. However, the high-throughput measurements of interfacial microstructure are difficult and inefficient for experimental methods (e.g., atomic force microscopy ). Currently, simulations and theories have become increasingly irreplaceable for microstructure evaluation and molecular design. Despite the success and accuracy of Monte Carlo (MC) and molecular dynamics (MD) simulations, it remains challenging due to the computational cost. For example, the charged PBs require special methods to compute the long-range Coulomb interactions, which needs long runtimes to guarantee the data reliability in the MC/MD simulations. Differently, the theoretical approach provides a low-cost alternative for the systematical study of PBs by controlling a series of key parameters such as grafting density, chain length, block features, etc. Specifically, Alexander and de Gennes 18 pioneeringly proposed a simple scaling theory based on a step-function density distribution to analyze the thermodynamic properties of PBs. Later, self-consistent field theory was adopted to study PBs, and presented a parabolic density distribution under specific conditions. In recent years, Lian et al. captured the parabolic-like density distribution of PBs with the help of lattice density functional theory (DFT).