The internal flow in an evaporating human blood plasma drop

Hypothesis: The internal flow in an evaporating blood plasma sessile drop is different from that in a water drop. The presence of plasma protein molecules, which are adsorbed on the plasma-air interface, suppresses the Marangoni flow on the interface and makes natural convection visible. The coexistence of natural convection and capillary flow is responsible for the characteristic peripheral convex dried pattern of the plasma drop. Experiments: (1) To observe the real-time internal flow in an evaporating plasma drop. (2) To investigate the mechanism of natural convection in the evaporating plasma drop. (3) To study the suppression of Marangoni flow caused by different plasma proteins. (4) To investigate the synergy of natural convection and capillary flow in material transport in the evaporating plasma drop. Finding: (1) Natural convection in the evaporating plasma drop is observed and supported by numerical simulations. (2) The suppression of Marangoni convection by the plasma proteins is the original cause for its internal flow to be different from that in a water drop. (3) Different plasma proteins have different suppression efficiencies to the Marangoni convection. (4) Interaction between the capillary flow and natural convection determines the material transport mechanism of the evaporating plasma drop and its desiccation pattern.