A buckling-based metrology for measuring the elastic moduli of polymeric thin films

Abstract

As technology continues towards smaller, thinner and lighter devices, more stringent demands are placed on thin polymer films as diffusion barriers, dielectric coatings, electronic packaging and so on. Therefore, there is a growing need for testing platforms to rapidly determine the mechanical properties of thin polymer films and coatings. We introduce here an elegant, efficient measurement method that yields the elastic moduli of nanoscale polymer films in a rapid and quantitative manner without the need for expensive equipment or material-specific modelling. The technique exploits a buckling instability that occurs in bilayers consisting of a stiff, thin film coated onto a relatively soft, thick substrate. Using the spacing of these highly periodic wrinkles, we calculate the film's elastic modulus by applying well-established buckling mechanics. We successfully apply this new measurement platform to several systems displaying a wide range of thicknessess (nanometre to micrometre) and moduli (MPa to GPa).

Bending Induced Self-Organized Switchable Gratings on Polymeric Substrates

“…In the curse of these studies it was also found that groove spacing was independent on the bending magnitude initially applied to the foil to produce the surface cracking. This behavior contrasts with the reported behavior of wrinkled PDMS surfaces where wrinkling-related diffraction effects are tightly dependent on the thickness of the stiff films coating the PDMS and on the magnitude of the experienced strain [5][6][7]26,27 . Other studies about cracking of thin films on compliant substrates also reveal that the average inter-crack distance is always inversely proportional to the strain [11][12][13][14] .…”

The role of substrate pre-stretch in post-wrinkling bifurcations

“…This degree of variability is apparently due to slight differences in the position of the sample relative to the UV light source during oxidation. Using the approach of Stafford and co-workers [49] , the effective thicknesses of the silicate layers are estimated for each sample with no substrate prestretch as h f = 3 -8 µm, with shear moduli of µ f = 620 kPa -3.8 MPa, corresponding to modulus mismatch values (µ f /µ s ) of 50 -300. These large ranges in effective film thickness and modulus are the result of variations between different samples.…”

“…MPa as determined by fitting the dependence of the wrinkle amplitude and wavelength on film strain for samples with no substrate pre-stretch via the classical buckling equations as described by Stafford and others [12,16] . For any given sample, the respective uncertainties in these quantities were less than 0.6 µm and 50 kPa; the large ranges determined for different samples therefore presumably reflect slight differences in sample position within the UV/O 3 cleaner.…”

A review on the role of interface in mechanical, thermal, and electrical properties of polymer composites

“…Therefore, the dispersion, interfacial adhesion, geometric dimensions, etc., play key roles in mechanical property enhancement [76,[129][130][131]. The mechanical properties can be evaluated by either conventional methods such as dynamic mechanical analysis (DMA) [27,132]; tensile, compression, and shear tests [25,[133][134][135]; or the new methods such as copper grid technique [136,137] and strain-induced elastic buckling instability for mechanical measurements [138][139][140]. Since stiffness is not significantly affected by the degree of interfacial bonding in polymer composites [141,142], it is not reviewed here.…”