Transport and assembling microparticles via Marangoni flows in heating and cooling modes

The processes of the particles transfer in liquid media and the creation of structures of required configurations on substrates are of great importance in such areas as materials science, coatings, optoelectronics and biomedical researches. To control of the transfer of large ensembles of particles and dynamically transform of the particle aggregates the precise and flexible methods are strongly required. In this work, we propose a method for manipulation of microparticles in volatile liquid layers hundreds of microns thick that relies on the control of Marangoni flows by changing a sign of the temperature gradient in the liquid by the local action of the heat source and/or the heat sink. We have clearly demonstrated the applicability of the method to perform of wide range of manipulations with the particle ensembles: particles assembling in the circular patterns on a substrate when heating is applied, transfer of particles away from a heat sink when the substrate is cooled, and creation of ring-like patterns by changing the temperature gradient sign during particle assembling process. We have also studied the influence of the liquid layer thickness on the particle transfer and the size of the resulting pattern. It was found out that when heating the final pattern area on substrate decreases with the layer thickness, while the time of the pattern formation increases with the layer thickness. In the cooling mode, the final cleaned area decreases with the number of particles but the dependence on the layer thickness is ambiguous. The characteristic time decreases with an increase in the number of particles and slightly increases with the layer thickness. It was also revealed that the increase in the layer thickness makes it possible to create the multilayer dense circular assemblies of particles. The proposed method is simple for implementation, flexible and can be applied for manipulation with particles of any physicochemical properties and shapes. The method is applicable for controlling both a single microparticle and a large group of particles.