Controlling the dynamics of a bidimensional gel above and below its percolation transition.
The morphology and the microscopic internal dynamics of a bidimensional gel formed by spontaneous aggregation of gold nanoparticles confined at the water surface are investigated by a suite of techniques, including grazing-incidence x-ray photon correlation spectroscopy (GI-XPCS). The range of concentrations studied spans across the percolation transition for the formation of the gel. The dynamical features observed by GI-XPCS are interpreted in view of the results of microscopic imaging; an intrinsic link between the mechanical modulus and internal dynamics is demonstrated for all the concentrations. Our work presents an example of a transition from a stretched to a compressed correlation function actively controlled by quasistatically varying the relevant thermodynamic variable. Moreover, by applying a model proposed some time ago by Duri and Cipelletti [Europhys. Lett. 76, 972 (2006)] we are able to build a master curve for the shape parameter, whose scaling factor allows us to quantify a "long-time displacement length." This characteristic length is shown to converge, as the concentration is increased, to the "short-time localization length" determined by pseudo-Debye-Waller analysis of the initial contrast. Finally, the intrinsic dynamics of the system is then compared with that induced by means of a delicate mechanical perturbation applied to the interface.
Department of Physics and Earth Sciences, University of Parma, Viale Usberti 7/A, I-43124 Parma, Italy.
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Orsi
European Synchrotron Radiation Facility, Boîte Postale 220, F-38043 Grenoble, France.
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Ruta
European Synchrotron Radiation Facility, Boîte Postale 220, F-38043 Grenoble, France.
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Chushkin
Department of Chemistry and Industrial Chemistry, University of Pisa, Via Risorgimento 35, I-56126 Pisa, Italy.
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Pucci
Department of Chemistry and Industrial Chemistry, University of Pisa, Via Risorgimento 35, I-56126 Pisa, Italy.
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Ruggeri
IMEM-CNR Institute, Parma Science Park, I-43124 Parma, Italy.
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Baldi
Department of Physics and Earth Sciences, University of Parma, Viale Usberti 7/A, I-43124 Parma, Italy.
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Rimoldi
Department of Physics and Earth Sciences, University of Parma, Viale Usberti 7/A, I-43124 Parma, Italy.
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Cristofolini