Berlin 2012 – scientific programme

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O: Fachverband Oberflächenphysik

O 58: Poster Session III (Solid/liquid interfaces; Metals; Semiconductors; Oxides and insulators)

O 58.2: Poster

Wednesday, March 28, 2012, 18:15–21:45, Poster B

Measuring hydrodynamic force on soft materials — •Farzaneh Kaveh, Michael Kappl, and Hans-Jürgen Butt — Max-Planck Institute for Polymer Research, Mainz, Germany.

Hydrodynamic drainage occurs when two surfaces approach each other in liquid. When the distance between the surfaces becomes small, the confined liquid in the gap is squeezed out. At high approaching velocity, the shear rate is high, causing a hydrodynamic force. Recent measurements have shown that at such a high shear rate, the no slip boundary condition may break down, even in the case of complete wetting. Hydrodynamic force at the nanometre scale has been measured on hard substrates and on bubbles in other works [1]. We aim to measure hydrodynamic force on soft substrates and apply a model which has been developed for deformable interfaces [2]. The goal is to understand the influence of soft substrates on hydrodynamic boundary condition at different velocities. The measurements are carried out by atomic force microscopy (AFM) using fresh cured polydimethylsiloxane (PDMS) as a soft substrate and 10 µm borosilicate glass spheres attached to a tip-less cantilever (colloidal probe technique). We record forces at approaching velocities of 0.5-120 µm/s. At low velocities, i.e., low shear rates no slip will occur. At high approaching velocities, slip may occur and should be visible in the hydrodynamic force.

[1] Bonaccurso E., Butt H.-J., Craig V.S., Phys. Rev. Lett. 90, 144501 (2003).

[2] Carnie S.L., Chan D.Y.C., Lewis C., Manica R., Dagastine R.R., Langmuir 21 (7), 2912 (2005).