Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 30: Poster: Micro and Nanofluidics

CPP 30.16: Poster

Wednesday, March 24, 2010, 17:30–19:00, Poster C

Slip length of thin polymer films on substrates with different hydrophobic layers — •Mischa Klos, Matthias Lessel, and Karin Jacobs — Saarland University, Experimental Physics, D-66123 Saarbrücken

The typical volume-to-surface fraction in fluid channels of modern microfluidics is getting smaller and smaller, so the solid/liquid interface becomes more and more important. In classic hydrodynamics, the velocity of a liquid at a channel wall is zero. Yet, a non-zero velocity at the interface could greatly enhance the throughput. This phenomenon is known as 'slippage' with the slip length characterizing its strength. For polymer melts, slippage can be achieved by a hydrophobic coating on, e.g., a Si wafer. The slip length can be inferred from the profile of the liquid front during dewetting of the film. We show the impact of different hydrophobic coatings on silicon substrates on the slip length. As coatings we use an amorphous Teflon (AF1600) layer and silanes with different chain lengths. The Teflon induces nearly no slip whereas the silanes (Octadecyltrichlorosilane (OTS), Dodecyltrichlorosilane (DTS)) provoke slip lengths in the range of micrometers (OTS) to tens of micrometers (DTS). The open question is why a difference between 12 (DTS) and 18 (OTS) carbon atoms on the backbone of the silane molecule can be responsible for the different slip lengths. To answer this question we investigate the dewetting on Hexadecyltrichlorosilane (HTS) with 16 carbon atoms on the back bone.