Dry versus Wet Particle Assembly: Toward Solvent-Free Fabrication.

For over three decades, the continuous demand for miniaturized devices has prompted scientists to explore the fundamental principles of colloidal or particle (10 nm to 10 μm) assembly to construct large ordered structures. So far, most of the assembly has been performed in wet conditions, i.e., in a solution. Over the past decade, solvent-free (or dry) assembly methods have gained more attention, offering a more sustainable alternative. In this perspective, we highlight the promising aspects of the dry assembly method, which is not only easy to use, rapidly performed, and clean but also abandons the use of solvents while ensuring that the quality of the created particle assembly matches or exceeds that of wet particle assemblies. However, challenges remain for ordered multilayers, binary layers, and nonspherical particle assemblies due to strong surface forces and limited control. Learning from strategies used in wet assembly and gaining a deeper fundamental understanding of surface interactions at the micro- and nanoscale could help bridge these gaps. In this perspective, the challenges and opportunities of dry particle assembly are thoroughly explored, providing a roadmap for advancing the solvent-free assembly field and contributing to a more sustainable world.