New Perspective of Mitigating the Coffee-Ring Effect: Interfacial Assembly

The evaporation of particle-laden droplets on a substrate usually results in ring-like deposits due to particle migration to the contact lines. This ubiquitous phenomenon, known as the coffee-ring effect (CRE), was initially observed in drying coffee droplets and later in many colloidal systems. The CRE has been intensively investigated during the past two decades to unveil the complexity related to its flow patterns, evaporation physics, and deposition structures after solvent evaporation. However, the contribution of colloidal particle assembly and interactions at the air-liquid interface of sessile droplets to the particle deposition requires more attention. The objective of this Review Article is to highlight the recent advances in mitigating or totally suppressing the CRE by means of interfacial assembly via manipulating the multibody interactions, for example, particle-particle, particle-substrate, particle-flow, and particle-interface interactions. Well-ordered monolayer deposition of the colloidal particles, driven by interfacial assembly, has been demonstrated by several research groups. This unique perspective of suppressing the CRE and creating well-ordered monolayer structures by assembling colloidal particles at the air-liquid interface creates a new paradigm in generating coatings and functional devices through liquid processing. General rules and guidelines are established to provide broader prospects of engineering desirable structures of colloidal particle deposition and assembly.