Progress on the layer-by-layer assembly of multilayered polymer composites: Strategy, structural control and applications

The environment-material interface plays a key role in determining the performance of a material in a variety of applications such as separating gas molecules or solutes, harnessing photons or electrons, and responding to biomolecules or organisms. Layer-by-layer assembly (LbL) technologies provide a means of controlling the surface and interface of a material, resulting in a composite in which the interface and the bulk of the material can be designed and controlled to a large extent independently. In addition, some exciting and novel applications have been widely studied for LbL assembly, such as vibration damping composites, shape memory materials, advanced dielectric composites, and radiation protection composites. In this paper, we review the development history and state-of-the-art of LbL assembly, and highlight the limitations of traditional LbL assembly in polymer solutions. As the forced assembly technology is simple, fast, and widely used for polymer substrates, it has attracted extensive attention and shows potential for application. Moreover, with the emergence of a new strategy and mechanism of LbL assembly (e.g., assembly with polymer crystallization) and the expansion of application fields, a comprehensive review focusing on the progress of LbL assembly in recent years is still lacking, which is the motivation for this review. Topics such as morphological characterization and control methods, the resulting multilayered interfaces, and their outstanding properties are discussed. A general but comprehensive review covering all aspects of the LbL assembly from mechanism to application has been carried out.