18 research outputs found
MicroMegascope
Atomic Force Microscopy (AFM) allows to reconstruct the topography of surface
with a resolution in the nanometer range. The exceptional resolution attainable
with the AFM makes this instrument a key tool in nanoscience and technology.
The core of the set-up relies on the detection of the mechanical properties of
a micro-oscillator when approached to a sample to image. Despite the fact that
AFM is nowadays a very common instrument for research and development
applications, thanks to the exceptional performances and the relative
simplicity to use it, the fabrication of the micrometric scale mechanical
oscillator is still a very complicated and expensive task requiring a dedicated
platform. Being able to perform atomic force microscopy with a macroscopic
oscillator would make the instrument more versatile and accessible for an even
larger spectrum of applications and audiences. We present for the first time
atomic force imaging with a centimetric oscillator. We show how it is possible
to perform topographical images with nanometric resolution with a grams tuning
fork. The images presented here are obtained with an aluminum tuning fork of
centimeter size as sensor on which an accelerometer is glued on one prong to
measure the oscillation of the resonator. In addition to the stunning
sensitivity, by imaging both in air and in liquid, we show the high versatility
of such oscillator. The set up proposed here can be extended to numerous
experiments where the probe needs to be heavy and/or very complex as well as
the environment
Multi-Sensorial Interface for 3D Teleoperation at Micro and Nanoscale
International audienceThis paper presents the design of a new tool for 3D manipulations at micro and nanoscale based on the coupling between a high performance haptic system (the ERGOS system) and two Atomic Force Microscope (AFM) probes mounted on quartz tuning fork resonators, acting as a nano tweezers. This unique combination provides new characteristics and possibilities for the localization and manipulation of (sub)micronic objects in 3 dimensions. The nano robot is controlled through a dual sensorial interface including 3D haptic and visual rendering, it is capable of performing a number of real-time tasks on different samples in order to analyse their dynamic effects when interacting with the AFM tips. The goal is then to be able to compare mechanical properties of different matters (stiffness of soft or hard matter) and to handle submicronic objects in 3 dimensions
Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces
International audienceRoom-temperature ionic liquids (RTILs) are molten salts which exhibit unique physical and chemical properties, commonly harnessed for lubrication and energy applications. The pure ionic nature of RTIL leads to strong electrostatic interactions among the liquid, furthermore exalted in the presence of interfaces and confinement. In this work, we use a tuning-fork-based dynamic surface force tribometer, which allows probing both the rheological and the tribological properties of RTIL films confined between a millimetric sphere and a surface, over a wide range of confinements. When the RTIL is confined between metallic surfaces, we see evidence of an abrupt change of its rheological properties below a threshold confinement. This is reminiscent of a recently reported confinement-induced capillary freezing, here observed with a wide contact area. In parallel, we probe the tribological response of the film under imposed nanometric shear deformation and unveil a yielding behavior of the interfacial solid phase below this threshold confinement. This is characterized by a transition from an elastic to a plastic regime, exhibiting striking similarities with the response of glassy materials. This transition to yielding of the RTIL in metallic confinement leads overall to a reduction in friction and offers a self-healing protection of the surfaces avoiding direct contact, with obvious applications in tribology
Pairwise frictional profile between particles determines discontinuous shear thickening transition in non-colloidal suspensions
International audienceThe process by which sheared suspensions go through a dramatic change in viscosity is known as discontinuous shear thickening. Although well-characterized on the macroscale, the microscopic mechanisms at play in this transition are still poorly understood. Here, by developing new experimental procedures based on quartz-tuning fork atomic force microscopy, we measure the pairwise frictional profile between approaching pairs of polyvinyl chloride and cornstarch particles in solvent. We report a clear transition from a low-friction regime, where pairs of particles support a finite normal load, while interacting purely hydrodynamically, to a high-friction regime characterized by hard repulsive contact between the particles and sliding friction. Critically, we show that the normal stress needed to enter the frictional regime at nanoscale matches the critical stress at which shear thickening occurs for macroscopic suspensions. Our experiments bridge nano and macroscales and provide long needed demonstration of the role of frictional forces in discontinuous shear thickenin
MicroMegascope based dynamic Surface Force Apparatus
Surface Force Apparatus (SFA) allows to accurately resolve the interfacial properties of fluids confined between extended surfaces. The accuracy of the SFA makes it an ubiquitous tool for the nanoscale mechanical characterization of soft matter systems. The SFA traditionally measures force-distance profiles through interferometry with subnanometric distance precision. However, these techniques often require a dedicated and technically demanding experimental setup, and there remains a need for versatile and simple force-distance measurement tools. Here we present a MicroMegascope based dynamic Surface Force Apparatus capable of accurate measurement of the dynamic force profile of a liquid confined between a millimetric sphere and a planar substrate. Normal and shear mechanical impedance is measured within the classical Frequency Modulation framework. We measure rheological and frictional properties from micrometric to molecular confinement. We also highlight the resolution of small interfacial features such as ionic liquid layering. This apparatus shows promise as a versatile force-distance measurement device for exotic surfaces or extreme environments