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Polymer Adhesion : Applying New Tools to Old Questions

Chelsea S. Davis National Institute of Standards and Technology,Gaithersburg, USA

In rubber manufacturing, two layers of uncrosslinked rubber are brought into contact and required to adhere to one another very rapidly. The scientific details governing the formation and adhesive strength of these short contacts are not well understood. Several studies have sought to characterize the cohesion of uncrosslinked viscoelastic polymers as a function of contact time. Our current study seeks to more reliably quantify this dependence of adhesion on contact time by utilizing a custom-built testing apparatus which allows us to have unprecedented control over all aspects of a contact adhesion test (approach and retraction velocities, maximum contact pressure, and contact time). This device is able to implement contact times over several orders of magnitude ranging from 0.03s to 100s. We have investigated the contact time effects of three unique contact scenarios : elastomer-silica, styrene-butadiene rubber (SBR) – silica, and SBR-SBR. With these three samples, we can decouple the effects of intermolecular forces, wetting/contact area, and chain interpenetration respectively.

In fundamental composite theory, the nature of the interface is often the key parameter which determines the strength of the resulting composite structure. While it is possible to observe interfacial failure and characterize the areal coverage of the matrix on the surface of the reinforcement phase in conventional composite materials, directly quantifying interfacial strength and contact area in a nanocomposite becomes far more difficult. A novel solution developed at NIST has been to utilize Förster resonance energy transfer (FRET) imaging[1,2] by preferentially labeling the interface within a nanocomposite system, allowing direct imaging of the interface with an optical microscope.[3] Zammarano et al. have shown that the incorporation of a FRET dye pair onto the surface of a cellulosic nanoreinforcement phase (dye 1) and within a polymer matrix (dye 2) allows visualization of the nanoscopic interphase region as the two dyes transfer energy on the same scale as the interphase depth (1 nm-100 nm).[3,4]

Building upon this FRET-based interfacial characterization technique, our goal is to develop a globally nondestructive measurement system that allows the quantitative characterization of key interfacial properties. As a first proof of concept, we will utilize FRET to observe nanoscopic interfacial fracture through the use of a classic double cantilever beam crack opening experiment.

Topic Area : Interface characterization, Measurement techniques, Fluorescence microscopy, contact mechanics, Adhesion

[1] T. Förster, Ann. Phys. 1948, 248.

[2] E. a Jares-Erijman, T. M. Jovin, Nat. Biotechnol. 2003, 21, 1387.

[3] M. Zammarano, P. H. Maupin, L.-P. Sung, J. W. Gilman, E. D. McCarthy, Y. S. Kim, D. M. Fox, ACS Nano 2011, 5, 3391.

[4] C. Berney, G. Danuser, Biophys. J. 2003, 84, 3992.