Design of a flexure for surface forces apparatus

We report the design of a variation of a double cantilever flexure system used for the measurement of displacement and force in surface force apparatus (SFA). The new force sensor is called dual double cantilever. The simple cantilever flexure suffers rotation, sideways deflection, and thermal expansion at the free end when loaded normally and asymmetrically. In the double cantilever these errors are minimized to a second order. In the dual double cantilever flexure the stiffness is enhanced 16 times as that of a single cantilever flexure but the rotation, sideways deflection, and thermal expansion at the free end are brought to many orders below the instrument resolutions. The new design enables the measurement of deflection by optical and capacitive sensing methods. The stiffness and the strain of the aluminum alloy [AUG1(2024)] flexure were estimated [dimensions, length (l=50.5 mm), breadth (b=10.5 mm), and thickness (t=1.2 mm)] by finite element method and were also validated experimentally. The finite element method was also used to create a map for the selection of a flexure geometry relevant to the properties of material under investigation by a SFA or a nanoindenter

Measurement of stiffness and damping constant of self-assembled monolayers

We design and fabricate an apparatus which uses two dual double cantilever flexures to probe mechanical properties of self-assembled monolayers (SAM) under compression. The cantilevers were designed to give stiffness of the same order as the SAM. One of the cantilevers carrying the probe is vibrated sinusoidally at subresonance frequency and subnanometric amplitude while the dynamic response of the other carrying the SAM is recorded in the contact mode to yield data which could be deconvoluted to give stiffness and damping constant of the SAM under compression using a model of viscoelasticity. We validate the apparatus as well as the method of deconvolution by indenting bulk polytetrafluoroethylene and estimate mechanical properties of SAMs of different chain length and head group. The approach adopted here is able to distinguish in terms of mechanical properties a bulk polymer from a SAM and also between two SAMs of similar but subtly different structure