Mechanical Properties of Thin Polymer Films Within Contacts

Abstract

This chapter addresses the problem of the mechanical properties of thin polymer films geometrically confined within contacts between elastic substrates. Analytical contact mechanics solutions for coated substrates are used to derive, within the limits of confined contacts situations, an approximate oedometric solution for the indentation of a thin film lying on a more rigid substrate. From a discussion of this approximate model, it is shown that lateral contact methods are an interesting alternative to indentation experiments for the measurement of the visco-elastic properties of polymer films in their glass transition range or rubbery state. As an example, the hydrostatic pressure dependence of the viscoelastic properties of confined polymer films is analyzed in the light of lateral contact stiffness measurements. The effects of hydrostatic pressure on the onset of plastic flow within confined polymer coatings are also discussed.

Cyclic nonlinear behavior of a glassy polymer using a contact method

“…Mechanical properties of polymers being sensitive to hydrostatic pressure, 35 one could therefore tentatively attribute the long term changes in G * app to the decreasing contact pressure. Within the linear viscoelastic regime, strong effects of the contact pressure on the shear modulus were already reported by Chateauminois et al 32 in the glass transition zone using the same thin film contact geometry. To estimate the pressure sensitivity of the apparent shear modulus, measurements of G app were carried out as a function of contact pressure under conditions where kinetics effects are no longer involved.…”

“…Care has been taken to align the lateral loading axis with respect to the contact point to avoid the application of a torque to the lens. indentation behavior of the acrylate film under consideration, 32 this contact pressure was found to correspond to the boundary between the elastic and plastic indentation behavior for the considered film thickness and lens radius. It can be noted that this mean contact pressure at the onset of yield is much larger than the compression yield stress measured using bulk cylindrical specimens of the same acrylate (i.e., 37 MPa at 10 −2 s −1 and 25 • C).…”

“…Such a difference obviously arises from the differing loading geometry but it could also incorporate some hydrostatic pressure effects. As detailed in reference, 32 variations in the indentation yield stress of the studied acrylate film when the contact conditions are changed can be accounted for by the well known sensitivity of the yield properties of polymer to hydrostatic pressure. 33 During lateral contact experiments, a sinusoidal displacement with an amplitude ranging from 0.3 to 6 m is applied to the contact.…”

“…It is also noteworthy that, while our contact device was unable to detect any very significant pressure induced change in the linear storage modulus G at room temperature within the range 40-100 MPa, a measurable pressure dependence is observed in the large strain regime. If one recalls that the pressure dependence of the modulus of glassy polymers is drastically enhanced in the glass transition zone, 32,35 this difference in the presssure dependency of the shear behavior between the linear and nonlinear regimes could thus be interpreted as evidence of a depressed glass transition temperature in the loaded and deformed state. This hypothesis is further supported by the linear viscoelastic measurements reported in the next section.…”

Filtering out slow-scan drifts in atomic force microscopy images

“…In some cases, a quantitative comparison of images is desirable, for instance in order to follow the development of surface patterns [4] or wear features [5] to investigate the local deformation of a strained specimen [6][7][8][9] or to follow a crack propagation [10][11][12]. Filtering, flattening, etc.…”