Europhys. Lett., 59 (3), pp. 370–376 (2002) EUROPHYSICS LETTERS 1 August 2002 Bubbles creeping in a viscous liquid along a slightly inclined plane P. Aussillous and D. Qu´ er´ e Laboratoire de Physique de la Mati` ere Condens´ ee, URA 792 du CNRS Coll` ege de France - 75231 Paris Cedex 05, France (received 1 February 2002; accepted in final form 13 May 2002) PACS. 47.15.Gf – Low-Reynolds-number (creeping) flows. PACS. 68.15.+e – Liquid thin films. PACS. 83.50.Lh – Slip boundary effects (interfacial and free surface flows). Abstract. – We describe the upwards movement of an air bubble creeping along a slightly inclined plane immersed in a viscous liquid which totally wets the solid. After characterizing the shape of the static bubble under a horizontal plane, we tilt the plane and study the resulting motion. The bubble reaches a steady velocity, which is described as a function of the bubble size, the liquid viscosity and the tilting angle. We interpret our results by considering the viscous dissipation in the so-called dynamic meniscus, which is the zone where a lubricating film forms. Introduction. – We consider a tank filled with a viscous liquid, in which a bubble is introduced. If the upper boundary of the tank is tilted, the bubble creeps along this boundary once it has reached it (fig. 1). In the (common) situation where the liquid totally wets the solid, a thin lubricating film of thickness e forms between the bubble and the solid. We denote by V the bubble velocity and by α the tilting angle of the solid. The bubble moves at a constant velocity and an interesting practical problem is to under- stand the source of dissipation. First, we study the shape of a bubble under a horizontal plane immersed in a fluid. Then, we present measurements of creeping velocities, as a function of the bubble size, the nature of the liquid and the solid slope. Our experiment consists in placing in a tank of oil an air bubble of controlled size (we note R 0 the initial radius) below a planar solid. This solid is a transparent polymer (PMMA) sheet, with millimetric graduations engraved on the top surface. Then, the solid is slightly tilted. We measure the position x of the front meniscus as a function of time, from which we deduce the bubble velocity (V =dx/dt). Each run is typically 10 cm long, and the velocity is found to be constant all along the run. The experimental error on the measurement of V is of the order of 1%. The liquid is a viscous silicone oil (viscosity η = 970 mPa s, density ρ = 970 kg/m 3 ) of low surface tension (γ = 20 mN/m). The oil completely wets the solid, so that the bubble is in a situation of non-wetting. This is confirmed by a direct observation. Side views of the bubble show that it joins the solid tangentially: the “contact angle” of the bubble on the solid is 180 ◦ (see fig. 1). Furthermore, all the bubbles (even the smallest ones, c  EDP Sciences