The cover image is a graphical design based on a SEM image of stable aggregated particles via heteroaggregation. The core cationic particle is surrounded by anionic particles in a shell layer and the driving force is mainly electrostatic interaction. This stable aggregated particle is negatively charged due to the sulfonated copolymer present in the anionic particles in the shell layer. As presented by Su Jeong Han, Eric S. Daniels, E. David Sudol, Victoria L. Dimonie, and Andrew Klein on page 3601, each particle is prepared by conventional emulsion polymerization and heteroaggregation is carried out by mixing cationic and anionic latex.

As presented by Siu Ning Leung, Muhammad Omer Khan, Ellen Chan, Hani E. Naguib, Francis Dawson, Vincent Adinkrah, and Laszlo Lakatos-Hayward on page 3293, the scanning electron microscopy (SEM) image illustrates the uses of secondary filler (e.g., carbon fiber) to create a thermally conductive network among the primary filler (e.g., hexagonal boron nitride platelets). The high aspect ratio of the secondary filler enhances the development of a thermally conductive network in the polymer-matrix composites.