Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session Q4: Polymer Surface Instabilities |
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Sponsoring Units: DPOLY GSNP Chair: Alfred Crosby, University of Massachusetts Amherst Room: 306/307 |
Wednesday, March 18, 2009 11:15AM - 11:51AM |
Q4.00001: Elastic instabilities in rubber Invited Speaker: Materials that undergo large elastic deformations can exhibit novel instabilities. Several examples are described: development of an aneurysm on inflating a rubber tube; non-uniform stretching on inflating a spherical balloon; formation of internal cracks in rubber blocks at a critical level of triaxial tension or when supersaturated with a dissolved gas; surface wrinkling of a block at a critical amount of compression; debonding or fracture of constrained films on swelling, and formation of ``knots'' on twisting stretched cylindrical rods. These various deformations are analyzed in terms of a simple strain energy function, using Rivlin's theory of large elastic deformations, and the results are compared with experimental measurements of the onset of unstable states. Such comparisons provide new tests of Rivlin's theory and, at least in principle, critical tests of proposed strain energy functions for rubber. Moreover the onset of highly non-uniform deformations has serious implications for the fatigue life and fracture resistance of rubber components. \\[4pt] References: \\[0pt] R. S. Rivlin, Philos. Trans. Roy. Soc. Lond. Ser. A241 (1948) 379--397. \\[0pt] A. Mallock, Proc. Roy. Soc. Lond. 49 (1890--1891) 458--463. \\[0pt] M. A. Biot, ``Mechanics of Incremental Deformations'', Wiley, New York, 1965. \\[0pt] A. N. Gent and P. B. Lindley, Proc. Roy. Soc. Lond. A 249 (1958) 195--205. \\[0pt] A. N. Gent, W. J. Hung and M. F. Tse, Rubb. Chem. Technol. 74 (2001) 89--99. \\[0pt] A. N. Gent, Internatl. J. Non-Linear Mech. 40 (2005) 165--175. [Preview Abstract] |
Wednesday, March 18, 2009 11:51AM - 12:27PM |
Q4.00002: Creasing instability of solvent-swelled polymer films Invited Speaker: A thin layer of polymer bound to a rigid substrate develops compressive stresses when it is swelled by solvent, due to the constraint against lateral expansion imposed by the substrate. For sufficiently large stresses, the surface becomes unstable to a buckling mode in which tightly-folded ``creases'' form on the surface to relieve compressive stress. While this instability has been known in practice for more than a century, it remains poorly characterized and incompletely understood. I will describe experiments on model systems of surface-attached hydrogels to characterize the onset and growth mechanisms of creases, as well as methods that allow control of crease formation in both space and time. In addition to the implications that this instability has for any type of polymeric coating undergoing swelling, it also provides an opportunity to create surfaces with switchable topography and chemistry. [Preview Abstract] |
Wednesday, March 18, 2009 12:27PM - 1:03PM |
Q4.00003: The macroscopic delamination of thin films from elastic substrates Invited Speaker: The wrinkling and delamination of stiff thin films adhered to a polymer substrate have important applications in ``flexible electronics.'' The resulting periodic structures, when used for circuitry, have remarkable mechanical properties since stretching or twisting of the substrate is mostly accommodated through bending of the film, which minimizes fatigue or fracture. To date, applications in this context have used patterning of the substrate-film adhesion energy to produce a controlled array of delamination ``blisters.'' However, even in the absence of such patterning, blisters have a characteristic size. We use macroscopic experiments to study what sets the dimensions of these blisters in terms of the material properties, which we explain using a combination of scaling and analytical methods. This points to a novel method for determining the interfacial toughness. Finally, we suggest a number of design guidelines for the thin films used in flexible electronic applications. [Preview Abstract] |
Wednesday, March 18, 2009 1:03PM - 1:39PM |
Q4.00004: Elastic Instability and Pattern Formation in Confined Soft Elastomeric Films Invited Speaker: When a rigid flat object or a flexible plate is removed from a thin soft film, instability patterns appear at the interface in the form of bubbles or fingers. The wavelengths of these instabilities are independent of all material and geometrical properties of the system except the thickness of the film. These observations contrast the classical Saffman-Taylor type instability in which the instability pattern depends on the viscous and surface tension forces in addition to the thickness of the liquid film. In the case of elastic instability of the kind described here, the wavelength depends on the material properties of the films only when soft films of different elastic properties are separated from each other. In the later case, a co-operative instability mode develops, which is a non-linear function of the thicknesses and the elastic moduli of both the films. In contrast to the wavelengths of these instabilities, their amplitudes are strong functions of several material and geometric properties of the system. These problems can be analyzed using regular perturbation technique to obtain the excess deformations of the film over and above the base quantities. Furthermore, by estimating the excess energy of the system, it can be shown that instability develops when the films are critically confined. This point can be illustrated by pre-stretching the film or simply by adjusting the contact width between the film and the plate. The instabilities that develop at the interface are critical to understanding adhesion and friction of soft thin films as they act like nucleated interfacial cracks. We performed a simple experiment, in which a flat rigid glass prism is sheared off a soft elastomeric film. At a given tangential force, the prism starts to slide on the elastomeric film accompanied with the formation of bubbles at the interface due to elastic instability. These bubbles, the lateral dimensions of which are comparable to the thickness of the film, move across the interface with speeds 1000 times faster than the overall sliding speed of the prism. The process continues till the critical condition for fracture is reached. These studies may shed some light on the fast dynamics of shear crack propagation in other systems. [Preview Abstract] |
Wednesday, March 18, 2009 1:39PM - 2:15PM |
Q4.00005: Micro-Origami: Elastic Instability of Polymer Films Invited Speaker: Upon compression, thin (rigid) elastic membranes supported on a soft elastic solid spontaneously deviate from their flat geometry by forming regular wrinkles. How can we control the wavelength and the symmetry of the wrinkle patterns? What is the influence of defects? Why should we observe focalisation of deformation in folds for large strains? During my talk, I will review our approaches to tackle these questions. [Preview Abstract] |
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