In addition to the hexagonally ordered clusters of levitating micro-droplets, a cluster with a chain structure can exist. The first systematic observation of this new phenomenon is reported in our paper:
A. A. Fedorets et al. “Self-arranged levitating droplet clusters: a reversible transition from hexagonal to chain structure” Langmuir https://doi.org/10.1021/acs.langmuir.9b03135

Water microdroplets condense over locally heated water-vapor interfaces and levitate in an ascending vapor-air flow forming self-assembled ordered monolayer clusters. The droplets do not coalesce due to complex aerodynamic interactions between them. The droplet cluster formation is governed by the condensation/evaporation balance and by coupling of heat flux and vapor flow with aerodynamic forces. Here we report the observations of a reversible structural transition from the ordered hexagonal-structure cluster to the chain-like structure and provide an explanation of its mechanism and conditions under which the transition occurs. The phenomenon provides new insights on the fundamental physical and chemical processes with microdroplets including their role in reaction catalysis in nature and their potential for aerosol and microfluidic applications.