Observation And Research Of Colloidal Particles Deposition During The Confined Droplet Evaporation Process

Under the microgravity environment, Fluid will exhibit special physical characteristics which different from ground environment. Space microgravity experiments have special experimental environment and scarcity of experimental opportunity, so before space science experiments, there are a lot of careful ground experiments to ensure foolproof Space Experiment. Recoverable satellite is an important means to achieve the experimental space science experiments. Chinese SJ-10 recoverable satellites will be launched in 2015. Colloidal material box is one of the payload, the scientific objectives of it is researching colloidal self-assembly and phase transition behavior when colloidal droplet evaporation process under microgravity in space. In this paper, some foundation ground researches are prepared as auxiliary matching explore for Colloidal material box.In this study, a confined hydrophilic region substrate is made, which can confined droplet in the hydrophilic region, which making droplet evaporation different from on the uniform hydrophilic or hydrophobic substrate. During evaporation, the contact radius is fixed and the contact angle changed from the super-hydrophilic angle to super-hydrophobic angle.Secondly, two analog devices are designed to simulating Space no buoyancy convection. Through finite element analysis flow field distribution inside the device to determine whether get simulated target. The main principle of analog devices is using temperature control means to suppress internal air buoyancy convection.Further, an experiment was done in the analog devices to determine the colloid droplet evaporation time. The main purpose is to determine the effective time of the evaporation space microgravity experiments and to provide a basis for the space experimental procedure of colloidal evaporation time.In the end, we research colloidal droplet evaporation physical process and the resulting deposition pattern on a confined round area by using an in situ optical observation system. This experiment is one of the ground experiments of space colloidal evaporation experiments which resulting will compare with the space experiment. In the particles deposition process, the main driven flow is different. The final deposition pattern was controlled by three flow behavior. In the early stage, the main flow is Marangoni flow, which drives the particles cluster float at the droplet surfaces, part of them accumulated at the boundary. As the evaporation proceeding, when the apparent contact angle decreased(<60°), the evaporation flux becomes singular near the contact line, Capillary flow towards the contact inside the drop as compensation to the solvent loss of the drop boundary, which drives the particles in the droplet rapidly accumulating at the contact-line. In the last evaporation stage, the thickness of the film in the hydrophilic area became very thin, and there is only one layer of particles in the this thin film, the thin liquid film instability triggers the particles in the middle area rapid aggregate and then forms a kind of network pattern, due to the distance between the particles decrease, Capillary force between particles also take part in this aggregate process.