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Nanomécanique et dynamique des polymères par microscopie de force en contact intermittent

Abstract : This report presents a study of polymers nanoscale properties using Atomic Force Microscopy in amplitude and frequency modulation modes. It starts by the determination of the physical origins of contrast in AFM images of triblock copolymer surfaces. This contrast is shown to be solely due to nanometric variations of viscoelastic properties (i.e. no topographic contribution is found in it). In a next step the local physical constants of the two nano-phases of the copolymer are evaluated thanks to an analytical and numerical modelling of the nonlinear dissipative interaction between oscillator and polymer sample. Then, a turning point experimental result shows that, in amplitude modulation mode with a sufficiently high quality factor Q, a soft material can appear as a hard one, so that its undeformed structure can be probed. Practically, this means that local mechanical properties or topography of sufficiently soft samples can be selectively accessed by varying Q. The last part is a study of the scale dependent viscoelasticity of a melt of entangled polymer chains, an hevea rubber sample, with the frequency modulation mode and a very high Q factor: when tip-polymer indentation and interaction time reach threshold values, a sharp increase of the drive power needed to maintain a constant oscillation amplitude is measured. It is shown to be due to a transition from a fast relaxation process of the polymer (<10-8 s Rouse-like motion at weak indentations) to a much slower one (>10-5 s disentanglement process as the size of the indented object goes beyond the entanglement length). This transition corresponds to a few angstroms variation of indentation depth.
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Contributor : Fabien Dubourg <>
Submitted on : Monday, October 25, 2004 - 11:30:51 AM
Last modification on : Monday, January 22, 2018 - 11:02:02 AM

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Fabien Dubourg. Nanomécanique et dynamique des polymères par microscopie de force en contact intermittent. Dynamique des Fluides [physics.flu-dyn]. Université Sciences et Technologies - Bordeaux I, 2002. Français. ⟨tel-00007198⟩

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