Molecular mechanics and performance of crosslinked amorphous polymer adhesives

Abstract

Amorphous polymers are among the most common materials used in adhesives, and a clear understanding of the effects of molecular scale features on macroscopic responses is necessary to design new, better performing adhesives. While many features have been investigated, including effects of molecular weight, inclusion of filler materials, and some effects of crosslinking, much of the understanding of the adhesive response remains empirical. Specifically, choosing the appropriate combination of polymer properties that optimize the work required to debond is still a challenge and the interplay between mechanical and chemical properties of polymers at interfaces is largely unknown. Here, we perform molecular dynamics simulations on a simple coarse-grained polymer model to directly investigate the role of crosslinking in determining the adhesive response of amorphous polymers at the molecular level. We find that crosslinking has a dramatic effect on the mechanical properties even at relatively low crosslink densities, and that crosslinking alone can be effective for optimizing the adhesive response of amorphous polymer adhesives. We observe a clear transition from cohesive to adhesive failure as the crosslink density is increased which coincides with the optimal toughening in the films. Furthermore, we find that our model captures the key molecular scale deformation mechanisms that control the adhesive response. For low crosslink densities, increased crosslinking improves the adhesive response by inhibiting chain sliding and allowing the structures to achieve large deformations, but as the crosslink density is increased further, the adhesive response is diminished due to reduced overall deformability. Our results provide simple but important insights into how crosslinking in amorphous polymer adhesives can be used to tune the mechanical response and ultimately to optimize adhesive performance for various applications.

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References

  1. 1.

    N.M. Pugno, S.W. Cranford, and M.J. Buehler: Synergetic material and structure optimization yields robust spider web anchorages. Small 9(16), 2747 (2013).

    CAS  Article  Google Scholar 

  2. 2.

    S.W. Cranford, A. Tarakanova, N.M. Pugno, and M.J. Buehler: Nonlinear material behaviour of spider silk yields robust webs. Nature 482 (7383), 72 (2012).

    CAS  Article  Google Scholar 

  3. 3.

    D.E. Barlow, G.H. Dickinson, B. Orihuela, J.L. Kulp, D. Rittschof, and K.J. Wahl: Characterization of the adhesive plaque of the barnacle Balanus amphitrite: Amyloid-like nanofibrils are a major component. Langmuir 26 (9), 6549 (2010).

    CAS  Article  Google Scholar 

  4. 4.

    M.J. Buehler, H.M. Yao, H.J. Gao, and B.H. Ji: Cracking and adhesion at small scales: Atomistic and continuum studies of flaw tolerant nanostructures. Modell. Simul. Mater. Sci. Eng. 14 (5), 799 (2006).

    Article  Google Scholar 

  5. 5.

    V. Sahni, T.A. Blackledge, and A. Dhinojwala: A review on spider silk adhesion. J. Adhes. 87 (6), 595 (2011).

    CAS  Article  Google Scholar 

  6. 6.

    Z. Qin and M.J. Buehler: Molecular mechanics of mussel adhesion proteins. J. Mech. Phys. Solids 62 (1), 19 (2014).

    CAS  Article  Google Scholar 

  7. 7.

    T.P.J. Knowles and M.J. Buehler: Nanomechanics of functional and pathological amyloid materials. Nat. Nanotechnol. 6 (8), 469 (2011).

    CAS  Article  Google Scholar 

  8. 8.

    Z. Qin and M.J. Buehler: Impact tolerance in mussel thread networks by heterogeneous material distribution. Nat. Commun. 4, 2187 (2013).

    Article  Google Scholar 

  9. 9.

    M.J. Buehler: Tu(r)ning weakness to strength. Nano Today 5 (5), 379 (2010).

    CAS  Article  Google Scholar 

  10. 10.

    C. Creton: Pressure-sensitive adhesives: An introductory course. MRS Bull. 28 (6), 434 (2003).

    CAS  Article  Google Scholar 

  11. 11.

    M.A. Krenceski and J.F. Johnson: Shear, tack, and peel of polyisobutylene — Effect of molecular-weight and molecular-weight distribution. Polym. Eng. Sci. 29 (1), 36 (1989).

    CAS  Article  Google Scholar 

  12. 12.

    I. Khan and B.T. Poh: Natural rubber-based pressure-sensitive adhesives: A review. J. Polym. Environ. 19 (3), 793 (2011).

    CAS  Article  Google Scholar 

  13. 13.

    C. Gay and L. Leibler: On stickiness. Phys. Today 52 (11), 48 (1999).

    Article  Google Scholar 

  14. 14.

    A. Zosel: Adhesive failure and deformation-behavior of polymers. J. Adhes. 30 (1–4), 135 (1989).

    CAS  Article  Google Scholar 

  15. 15.

    C.A. Dahlquist: Pressure-sensitive adhesives. In Treatise on Adhesion and Adhesives; R.L. Patrick ed.; Marcel Dekker: New York, 1969; p. 219.

    Google Scholar 

  16. 16.

    A.N. Gent and J. Schultz: Effect of wetting liquids on strength of adhesion of viscoelastic materials. J. Adhes. 3 (4), 281 (1972).

    CAS  Article  Google Scholar 

  17. 17.

    B.T. Poh, Y.F. Giam, and F.P.A. Yeong: Tack and shear strength of adhesives prepared from styrene-butadiene rubber (SBR) using gum rosin and petro resin as tackifiers. J. Adhes. 86 (8), 844 (2010).

    CAS  Article  Google Scholar 

  18. 18.

    B.T. Poh and A.T. Yong: Effect of molecular weight of epoxidized natural rubber on shear strength of adhesives. J. Appl. Polym. Sci. 114 (6), 3976 (2009).

    CAS  Article  Google Scholar 

  19. 19.

    B.T. Poh and A.T. Yong: Effect of molecular weight of rubber on tack and peel strength of SMR L-based pressure-sensitive adhesives using gum rosin and petroresin as tackifiers. J. Macromol. Sci. A 46 (1), 97 (2009).

    CAS  Article  Google Scholar 

  20. 20.

    B.T. Poh and A.T. Yong: Dependence of peel adhesion on molecular weight of epoxidized natural rubber. J. Adhes. 85 (7), 435 (2009).

    CAS  Article  Google Scholar 

  21. 21.

    B.T. Poh, P.G. Lee, and S.C. Chuah: Adhesion property of epoxidized natural rubber (ENR)-based adhesives containing calcium carbonate. Express Polym. Lett. 2 (6), 398 (2008).

    CAS  Article  Google Scholar 

  22. 22.

    H. Lakrout, C. Creton, D.C. Ahn, and K.R. Shull: Influence of molecular features on the tackiness of acrylic polymer melts. Macromolecules 34 (21), 7448 (2001).

    CAS  Article  Google Scholar 

  23. 23.

    M. Sherriff, R.W. Knibbs, and P.G. Langley: Mechanism for action of tackifying resins in pressure-sensitive adhesives. J. Appl. Polym. Sci. 17 (11), 3423 (1973).

    CAS  Article  Google Scholar 

  24. 24.

    S.D. Tobing and A. Klein: Molecular parameters and their relation to the adhesive performance of emulsion acrylic pressure-sensitive adhesives. II. Effect of crosslinking. J. Appl. Polym. Sci. 79 (14), 2558 (2001).

    CAS  Article  Google Scholar 

  25. 25.

    A. Zosel: Effect of cross-linking on tack and peel strength of polymers. J. Adhes. 34 (1–4), 201 (1991).

    CAS  Article  Google Scholar 

  26. 26.

    R. Auhl, R. Everaers, G.S. Grest, K. Kremer, and S.J. Plimpton: Equilibration of long chain polymer melts in computer simulations. J. Chem. Phys. 119 (24), 12718 (2003).

    CAS  Article  Google Scholar 

  27. 27.

    K. Kremer and G.S. Grest: Dynamics of entangled linear polymer melts — A molecular-dynamics simulation. J. Chem. Phys. 92 (8), 5057 (1990).

    CAS  Article  Google Scholar 

  28. 28.

    S.W. Sides, G.S. Grest, M.J. Stevens, and S.J. Plimpton: Effect of end-tethered polymers on surface adhesion of glassy polymers. J. Polym. Sci. Pol. Phys. 42 (2), 199 (2004).

    CAS  Article  Google Scholar 

  29. 29.

    S.W. Sides, G.S. Grest, and M.J.K. Stevens: Large-scale simulation of adhesion dynamics for end-grafted polymers. Macromolecules 35 (2), 566 (2002).

    CAS  Article  Google Scholar 

  30. 30.

    M.J. Stevens: Manipulating connectivity to control fracture in network polymer adhesives. Macromolecules 34 (5), 1411 (2001).

    CAS  Article  Google Scholar 

  31. 31.

    M.J. Stevens: Interfacial fracture between highly cross-linked polymer networks and a solid surface: Effect of interfacial bond density. Macromolecules 34 (8), 2710 (2001).

    CAS  Article  Google Scholar 

  32. 32.

    M. Tsige, C.D. Lorenz, and M.J. Stevens: Role of network connectivity on the mechanical properties of highly cross-linked polymers. Macromolecules 37 (22), 8466 (2004).

    CAS  Article  Google Scholar 

  33. 33.

    M. Tsige and M.J. Stevens: Effect of cross-linker functionality on the adhesion of highly cross-linked polymer networks: A molecular dynamics study of epoxies. Macromolecules 37 (2), 630 (2004).

    CAS  Article  Google Scholar 

  34. 34.

    W.J. Xia and S. Keten: Coupled effects of substrate adhesion and intermolecular forces on polymer thin film glass-transition behavior. Langmuir 29 (41), 12730 (2013).

    CAS  Article  Google Scholar 

  35. 35.

    W.J. Xia, S. Mishra, and S. Keten: Substrate vs. free surface: Competing effects on the glass transition of polymer thin films. Polymer 54 (21), 5942 (2013).

    CAS  Article  Google Scholar 

  36. 36.

    S. Plimpton: Fast parallel algorithms for short-range molecular-dynamics. J. Comput. Phys. 117 (1), 1 (1995).

    CAS  Article  Google Scholar 

  37. 37.

    W. Humphrey, A. Dalke, and K. Schulten: VMD: Visual molecular dynamics. J. Mol. Graph. 14 (1), 33 (1996).

    CAS  Article  Google Scholar 

  38. 38.

    G. Marsagli: Choosing a point from surface of a sphere. Ann. Math. Stat. 43 (2), 645 (1972).

    Article  Google Scholar 

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ACKNOWLEDGMENTS

We acknowledge support from Henkel Corporation. We acknowledge fruitful discussions with M. Hamm, C. Paul, and P. Palasz.

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Correspondence to Markus J. Buehler.

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Solar, M., Qin, Z. & Buehler, M.J. Molecular mechanics and performance of crosslinked amorphous polymer adhesives. Journal of Materials Research 29, 1077–1085 (2014). https://doi.org/10.1557/jmr.2014.82

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