Experiments and modeling on an air-water interface populated by biological molecules

Abstract : This thesis addresses flow-induced packing of amphiphilic bio-molecules along an air-water interface. Pentadecanoic acid (PDA) is selected as model system. Experiments are based on a shear flow provided in an annular channel whose floor is put in rotation. The liquid surface is covered by a Langmuir layer of PDA submitted to a bulk-driven shear at the liquid surface and to a 2-D shear along it, as well. Phase transition from liquid-expanded (LE) to liquid-condensed (LC) phases is observed under Brewster angle microscopy (BAM) and investigated based on area fraction distribution of the LC phase after permanent regime is established. The distribution of condensed phase demonstrates a radially-inwards packing along the liquid surface induced by centrifugation of the subphase. For a growing level of centrifugation, the Langmuir film experiences a strong morphological transition at meso scale, driven by a balance between surface shear and line tension. For a highly-densified PDA film, LC domains are stratifying. If sub-phase rotation is large enough (Re as large as 1000), bulk shearing is responsible for LC domains break-up in agreement with literature. An analytical modelling is proposed at a small Reynolds number with a new integral formulation which enables estimation of the Boussinesq number as well as the measurement of viscous stratification.
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Submitted on : Monday, November 2, 2009 - 5:59:14 PM
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Yu-Lin Huang. Experiments and modeling on an air-water interface populated by biological molecules. Fluid Dynamics [physics.flu-dyn]. Université Joseph-Fourier - Grenoble I, 2009. English. ⟨tel-00429430⟩

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