AIRCOAT
bioinspired air layer
Biomimetics: when science is
inspired by nature
The bioinspired technology mimics the floating water fern ‘Salvinia molesta’, which forms a permanent air layer when submerged in water and is able to maintain a stable air layer under pressure. That is the Salvinia Plant effect.
This ability is particularly important for drag-reducing ship coatings. This means that no additional air or energy has to be supplied and the air layer also remains effective when the ship is moving.
AIRCOAT project uses experimental and theoretical approaches to examine the contribution of this pinning effect for air-layer stability in different environments.
How does the Salvinia Plant
effect work?
Salvinia plant structure is composed of different hydrophobic pillars (repelling water) with hydrophilic tips (attracting water) at their ends, pinning the air–water interface. The special surface structure and properties of the coating establish and retain an air layer. That’s why the surface of Salvinia leaves is considered to be a biological model for technological air-retaining surfaces.
By applying the capillary adhesion technique, the adhesion forces of individual hairs to the water surface is determined to be about 20 μN per hair. Using confocal microscopy and fluorescence labelling, it is found that the leaves maintain a stable air layer under a pressure of up to 65 mbar.
Combining both results, overall pinning forces are obtained, accounting for only about 1% of the total air-retaining force. It is suggested that the restoring force of the entrapped air layer is responsible for the remaining 99%.
Air spring effect
This model of the entrapped air acting is verified as a pneumatic spring (“air-spring”) by an experiment – lead by Karlsruhe Institut Für Technologie (KIT) – short circuiting the air layer, which results in immediate air loss. Thus, the plant enhances its air-layer stability against pressure fluctuations by a factor of 100 by utilizing the entrapped air volume as an elastic spring.
KIT concluded that the air layer on the leaf requires a force to be expanded or compressed, serving as a spring that significantly reduces the movement of the air/water interface for a given pressure.
The shape of the resulting expanded air cushion is determined by the interaction of surface tension and the flexibility of the hairs. Only when a critical volume of the air layer is exceeded, the first contact points are lost, because the outward facing air/water interface pulls too strongly (>20 μN) on the pinning sites at the end of the hairs.
Bioinspired technology:
air layer laminate composition
The final AIRCOAT laminate is composed of four layers:
protection layer, AIRCOAT structure layer, adhesive layer,
paper protection.
Protection layer
The external layer (green layer) on the top of the AIRCOAT structure is here to avoid any distortion of the structure during the shipping, manipulation and application of the laminate. This layer is supposed to be removed once the laminate is applied on the hull.
AIRCOAT pillars structure
AIRCOAT structure is the most important layer and is in direct contact with the water. This is the surface structure made of pillars that establishes and retains the air. No additional air or energy has to be supplied. The air layer also remains effective when the ship is not moving.
This layer is made up of different sections, giving more flexibility and thus making the maintenance of the hull coating easier and limiting the expansion of any eventual air leak. Each square of the AIRCOAT layer reproduces the borders of Salvinia leaves, ensuring the effectiveness of the air cushion.
Adhesive layer:
high tack & high bound
AIRCOAT laminate is made for a long term marine application thanks to the high tack and high bound feature. It can be applied manually by applying pressure the layer with a squeegee. The protection layer is here to avoid any damage during the application.
Protection layer
The external layer (green layer) on the top of the AIRCOAT structure is here to avoid any distortion of the structure during the shipping, manipulation and application of the laminate. This layer is supposed to be removed once the laminate is applied on the hull.
AIRCOAT pillars structure
AIRCOAT structure is the most important layer and is in direct contact with the water. This is the surface structure made of pillars that establishes and retains the air. No additional air or energy has to be supplied. The air layer also remains effective when the ship is not moving.
This layer is made up of different sections, giving more flexibility and thus making the maintenance of the hull coating easier and limiting the expansion of any eventual air leak. Each square of the AIRCOAT layer reproduces the borders of Salvinia leaves, ensuring the effectiveness of the air cushion.
Adhesive layer:
a simple application
AIRCOAT laminate is very easy to apply, like a standard sticker. It can be applied manually by applying pressure the layer with a squeegee. The green protection layer is here to avoid any damage during the application.