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High Resolution Image Download MS PowerPoint Slide The recent discovery of a soft, elastomeric surface on polymer glasses is transforming our understanding of tribology, adhesion, and other interactions at material interfaces. Herein, we developed an approach to investigate the linear elasticity of the rubbery surface of glassy polymers by observing and modeling the deformation of these films in response to interfacial wetting forces. This method utilizes the surface tension of an immiscible liquid droplet to induce a well-defined deformation on the film surface, known as a wetting ridge. We establish a quantitative relationship between the height and width of the wetting ridge and the thickness and modulus of the rubbery surface layer. Measurements for polystyrene (PS), poly(4-methylstyrene) (P4MS), and poly( tert -butylstyrene) (PtBS) revealed that the surface-layer thickness is typically below 10 nm and is greater for PtBS than for PS and P4MS. Furthermore, the obtained surface elastic modulus was of the same order of magnitude as the rubbery plateau modulus of the bulk polymers but was consistently higher than the bulk values, indicating a stiffening of the rubbery response at the polymer-glass surface.
Zhang et al. (Fri,) studied this question.