Study of Elastic Modulus and Yield Strength of Polymer Thin Films Using Atomic Force Microscopy

Abstract

Nanometer-scale elastic moduli and yield strengths of polycarbonate (PC) and polystyrene (PS) thin films were measured with atomic force microscopy (AFM) indentation measurements. By analysis of the AFM indentation force curves with the method by Oliver and Pharr, Young's moduli of PC and PS thin films could be obtained as 2.2 ( 0.1 and 2.6 ( 0.1 GPa, respectively, which agree well with the literature values. By fitting Johnson's conical spherical cavity model to the measured plastic zone sizes, we obtained yield strengths of 141.2 MPa for PC thin films and 178.7 MPa for PS thin films, which are ∼2 times the values expected from the literature. We propose that it is due to the AFM indentation being asymmetric, which was not accounted for in Johnson's model. A correction factor, , of ∼0.72 was introduced to rescale the plastic zone size, whereupon good agreement between theory and experiment was achieved.

Nanomechanical properties of solvent cast polystyrene and poly(methyl methacrylate) polymer blends and self-assembled block copolymers

“…Apart from the influence of the rigid substrate, there are other phenomena that influence indentation experiments performed with an AFM. 10,19 Polymer thin film's glass transition temperature may increase or decrease with respect to bulk values depending on the film thickness and the interaction with the supporting substrate. 20 A (softer) liquid-like layer is probably present at the polymer-air interface, 21 even if its influence could be neglected due to the compression exerted by the tip during indentation.…”

“…9 It is known that when the indentation depth exceeds 20% of the thickness of the probed film, effects of the substrate underneath should be considered. 10 Second, we have probed the mechanical properties of randomly oriented poly(styrene-b-methylmethacrylate) (PS-b-PMMA) thin films. Thin films of PS-b-PMMA can self-assemble into ordered periodic structures at the molecular scale (5 to 50 nm), forming a rich variety of nanophase-separated structures such as lamellae or pillars.…”

Prism coupling technique investigation of elasto-optical properties of thin polymer films

“…8 Another method is the parallel plate capacitor method, where metal layers are deposited onto polymer surfaces, which could modify the mechanical properties of the film. 9 Other approaches include use of nanoindentor, 10 atomic force microscopy, 11 and precision capacitance dilatometry. 12 While all of these methods measure the out-of-plane mechanical properties of the polymer films, they do not measure optical properties simultaneously.…”

Study on elastic modulus of individual ferritin

“…With this method Schaer-Zammaretti and Ubbink [16] compared the surface stiffness of different bacteria. Moreover, FV mapping has also been extensively used in materials science [17,18] . For example, Shulha et al [19] quantitatively investigated the compression elastic properties of two kinds of dendritic molecules G3 and G4.…”