MicroMegascope based dynamic surface force apparatus

Abstract

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.

Nanorheology of Interfacial Water during Ice Gliding

“…S11 and Ref. [29]; (ii) ionic liquids were investigated using this protocole in a previous study, see Ref. [29] and, beyond the rheology, also evidenced molecular layering at the interface, confirming the sensitivity of the setup; (iii) the two modes (stroke-probe) methodology was successfully implemented to study the interfacial properties of liquids exhibiting complex (shear-thickening) rheology, beyond that of newtonian fluids, see Ref.…”

“…The lateral stroke of the sphere then shears the ice with an amplitude a T ∼ 1 − 30 µm and velocity U = 2πa T f T , typically up to 0.1 m.s −1 . A Phase-Lock-Loop (PLL) maintains the system at the resonance by tuning the excitation frequency f T and the tangential friction force F F is simply measured by tracking the excitation force F em T necessary to keep the oscillation amplitude a T constant while sliding according to [29]. Simultaneously, we take advantage of the higher order eigenmodes of the tuning fork: as sketched in Fig.…”

“…We investigate simultaneously the friction of a millimetric slider on ice, and the corresponding interfacial mechanical properties of the meltwater film at the nanoscale. To this end, we harvest the possibilities offered by a newly introduced force measurement apparatus [28,29], to realize here a "stroke-probe" tribometer with nanoscopic sensitivity. This apparatus allows us to close the gap between nano-and macro-scale tribometry [31], which is a prerequisite for the investigation of the ice interface under sliding.…”

Nanotribology of Ionic Liquids: Transition to Yielding Response in Nanometric Confinement with Metallic Surfaces

“…As in standard frequency modulation AFM [21] a conservative interaction leads to a shift of the oscillator resonance frequency f 0 → f 0 þ δf and a dissipative force implies an extra damping which broadens the resonance Q 0 → Q 0 − δQ. Despite the size of the force probe, this experimental setup was already shown to display the force sensitivity required for atomic force microscopy [21] and even detection of subnanometric layering of RTILs confined between a (insulating) mica surface and glass bead [22]. A voltage difference of ΔV ≈ 25 mV is furthermore applied between the gold surface and the gold-coated sphere [ Fig.…”

“…Furthermore, metallic surfaces are ubiquitous in applications of RTILs, e.g., for lubrication, where RTILs are expected to be excellent boundary lubricants [18,19], as well as in electrochemistry [20]. In the present work, we use a newly introduced force measurement methodology, based on a macroscopic tuning fork [21,22] and here combined with electric measurements, in order to probe the equilibrium and out-of-equilibrium frictional properties of RTILs confined between extended metallic surfaces. This instrument allows us to probe both the rheology of the confined materials, as well as its tribological properties under shear.…”