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کلوئیدها و سطوح الف: جنبه های فیزیکوشیمیایی و مهندسی
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  • on the relation between hierarchical morphology and mechanical properties of a colloidal 2d gel system

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    • تاریخ ارائه: 1392/07/24
    • تاریخ انتشار در تی پی بین: 1392/07/24
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     we study a bidimensional gel system formed by a langmuir film of gold nanoparticles. its morphology is thoroughly characterized by afm, sem, and ellipsometric imaging techniques and shows a complex structure with features on a hierarchy of different sizes following a levy distribution. the mechanical response arising after the gel point is investigated by interfacial shear rheometry. the film is found to be mainly elastic, with the mechanical moduli scaling as a power law of the reduced concentration, in the same way as the fluctuation time which was measured in a recent x-ray photon correlation spectroscopy experiment. the frequency dependence of the moduli is well described in the framework of the soft glass rheology model (sgr) [sollich et al. phys rev lett 78, 2020 (1997)]. in this theory a power law distribution of relaxation times is postulated, whose exponent is experimentally determined for the present case. such a distribution may reflect – in the dynamics – the hierarchical nature of the morphology of the film evidenced by microscopy. a mastercurve can be built, extending time–temperature to a time–concentration superposition principle as in [cicuta et al. phys rev lett 90, 116103(2003)]. this allows to describe the mechanical response over a frequency range slightly larger than that experimentally accessible. besides the sgr component, a viscous term is always present, whose origin is investigated also taking into account samples with different preparation histories.

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