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| - Equilibrium and Dynamic Adsorption of C12E5 at theAir−Water Surface Investigated Using Ellipsometry andTensiometry
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| - We have investigated the equilibrium and dynamic adsorption of n-dodecyl pentaoxyethylene glycolether (C12E5) at the air−water surface using both ellipsometry and tensiometry. Two simple models forthe monolayer structure were used to derive the equilibrium adsorption isotherm from ellipsometric dataand tested for their validity by comparison with neutron reflection and tension data. A monolayer modelcomprising a lower layer containing the ethoxy headgroups plus water and an upper layer containing thedodecyl tail groups was found to yield an isotherm consistent with all the data. The slow adsorptionkinetics (minutes to hours) was monitored using both ellipsometry and dynamic tension. Dynamic tensioncurves reconstructed from the ellipsometric data using the equilibrium adsorption isotherm were inagreement with measured dynamic tensions. The adsorption rate for a C12E5 monomer concentrationcorresponding to adsorption equal to 75% of the maximum adsorption was found to be diffusion controlled.Lower concentrations of C12E5 showed adsorption rates faster than diffusion-controlled adsorption, probablydue to convection.
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