IDENTIFICATION OF PHYSICO-CHEMICAL KEY FACTORS
OF SURFACE CONTAMINATION
SUMMARY
The objective of the CNRS and ESPCI team was to identify the key physico-chemical factors of surface contamination. To this aim, 3 distinct methods have been deployed: (i) Viscosity measurements of the bumblebee hemolymph over time on different substrates and for different temperatures through microrheology; (ii) observation of the wetting properties of different substrates and measurement of the adhesion of sessile coagulated drops on those substrates and (iii) model experiment of the motion of an insect sliding on a film of hemolymph under wind conditions.
CONCEPT
Standard rheological measurements of hemolymph have been determined with microrheology. The impact of the drop environment, the nature of the substrate or the temperature on hemolymph coagulation can be explored with this technique.
Wetting properties of the different coatings produced by CIDETEC (WP5) were assessed through measurements of advancing and receding contact angles of water while adhesion energy of hemolymph on those coating has been studied via a scraping test.
In order to capture the physical ingredients involved in the motion of a particle adhering to a viscous film under wind conditions, we designed a simplified model experiment. In this academic configuration, a sphere (of a certain radius and density) is deposited on a horizontal plate coated with a layer of silicone oil (of a certain thickness and viscosity). The sphere is displaced on the viscous layer thanks to a wind tunnel.
TECHNICAL ADVANTAGE
The advantages of the microrheology technique are:
Measuring contact angles is the common method to study the wetting properties of a substrate. This method is rapid, easily reproductible and the theory behind it is well established, allowing for a good interpretation of the measurements. On its side, the scrapping test requires a small quantity of hemolymph, is easily reproductible and avoids scrubbing the surface as it may damage the coating to analyze.
The model experiment of the motion of an insect sliding on a film of hemolymph under wind conditions aimed at capturing the physical ingredients involved in the motion of the body insect after impact adhering to the solid substrate through viscous hemolymph. The model is reminiscent of a previous study of a sphere rolling down an inclined lubricated surface [Bico 2009] already applied and validated by the scientific community.
INPUT IN STELLAR
The analysis performed by CNRS and ESPCI allows the identification of physico-chemical factors of surface contamination. The influence of the interface between different CIDETEC coatings and coagulating hemolymph have been explored through microrheology. In addition, CIDETEC coatings have been characterized by standard wetting measurements.