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Abstract: The self-assembly of two nonionic surfactants, pentaethylene glycolmonododecyl ether C12E5 and n-dodecyl-{\ss}-maltoside {\ss}-C12G2, in thepresence of a purpose-synthesized silica sol of uniform particle size diameter16 nm has been studied by adsorption measurements, dynamic light scatteringand small-angle neutron scattering SANS using a H2O-D2O mixture matching thesilica, in order to highlight the structure of the surfactant aggregates. ForC12E5 strong aggregative adsorption onto the silica beads, with a high plateauvalue of the adsorption isotherm above the CMC was found. SANS measurementswere made at a series of loadings, from zero surfactant up to maximum surfacecoverage. It is found that the spherical core-shell model nicely reproduces theSANS data up to and including the local maximum at q = 0.42 nm-1 but not in thePorod region of high q, indicating that the surface area of the adsorbedsurfactant is underestimated by the model of a uniform adsorbed layer. Asatisfactory representation of the entire scattering profiles is obtained withthe model of micelle-decorated silica beads, indicating that C12E5 is adsorbedas spherical micellar aggregates. This behaviour is attributed to the highsurface curvature of the silica which prevents an effective packing of thehydrophobic chains of the amphiphile in a bilayer configuration. For themaltoside surfactant {\ss}-C12G2 very weak adsorption on the silica beads wasfound. The SANS profile indicates that this surfactant forms oblate ellipsoidalmicelles in the silica dispersion, as in the absence of the silica beads.



Author: Dersy Lugo, Julian Oberdisse LCVN, Matthias Karg, Ralf Schweins ILL, Gerhard Findenegg

Source: https://arxiv.org/







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