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Figure 2 | SpringerPlus

Figure 2

From: Stability of the volume of air trapped on the abdomen of the water spider Argyroneta aquatica

Figure 2

Structure of the layer of hair covering the abdomen of the spider Argyroneta aquatica (schematic drawing). a: Vertical cut across three horizontally oriented neighbouring hairs on the abdomen (ab) of the spider. The hairs are part of a layer of the feathered hair with a hydrophobic surface trapping under water (w) a volume of air (a) on the surface of the abdomen. The feathered structure of the hair is presented in Figure 2 b by short “bristles” (short straight lines originating from the surface of the long hair covering the abdomen). To be specific, it is assumed that the solid structures have a hydrophobic surface. The tips of the bristles are in contact with water. The locations at which three phases (air - water - bristle) are in contact are marked by black dots (i.e. points of three-phase-contact). The air/water surface connecting two points of three-phase-contact is curved. The origin of the radius of curvature is located within the aqueous phase. b: Side view on the air (a)/water (w) surface of two short sections of the same or of two different long hairs (h) with a hydrophobic surface. Each section of the surface carries a bristle (br). Two points of three-.phase-contact are marked by small black dots which are a distance (2 r) apart. R e is the radius of curvature of the air/water surface connecting two points of three-phase-contact. The straight line marked by the symbol t is the tangent to the curved air/water surface at one of the points of three-phase-contact. The contact angle θe is measured across the liquid phase (by definition). The drawings refer to an arbitrary value of θe > 90°. The contact angle θe ' is given by: θe ' = 180° − θe.

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