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.
This is a preview of subscription content, access via your institution.
Buy single article
Instant access to the full article PDF.
Tax calculation will be finalised during checkout.
Subscribe to journal
Immediate online access to all issues from 2019. Subscription will auto renew annually.
Tax calculation will be finalised during checkout.
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).
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).
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).
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).
V. Sahni, T.A. Blackledge, and A. Dhinojwala: A review on spider silk adhesion. J. Adhes. 87 (6), 595 (2011).
Z. Qin and M.J. Buehler: Molecular mechanics of mussel adhesion proteins. J. Mech. Phys. Solids 62 (1), 19 (2014).
T.P.J. Knowles and M.J. Buehler: Nanomechanics of functional and pathological amyloid materials. Nat. Nanotechnol. 6 (8), 469 (2011).
Z. Qin and M.J. Buehler: Impact tolerance in mussel thread networks by heterogeneous material distribution. Nat. Commun. 4, 2187 (2013).
M.J. Buehler: Tu(r)ning weakness to strength. Nano Today 5 (5), 379 (2010).
C. Creton: Pressure-sensitive adhesives: An introductory course. MRS Bull. 28 (6), 434 (2003).
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).
I. Khan and B.T. Poh: Natural rubber-based pressure-sensitive adhesives: A review. J. Polym. Environ. 19 (3), 793 (2011).
C. Gay and L. Leibler: On stickiness. Phys. Today 52 (11), 48 (1999).
A. Zosel: Adhesive failure and deformation-behavior of polymers. J. Adhes. 30 (1–4), 135 (1989).
C.A. Dahlquist: Pressure-sensitive adhesives. In Treatise on Adhesion and Adhesives; R.L. Patrick ed.; Marcel Dekker: New York, 1969; p. 219.
A.N. Gent and J. Schultz: Effect of wetting liquids on strength of adhesion of viscoelastic materials. J. Adhes. 3 (4), 281 (1972).
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).
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).
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).
B.T. Poh and A.T. Yong: Dependence of peel adhesion on molecular weight of epoxidized natural rubber. J. Adhes. 85 (7), 435 (2009).
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).
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).
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).
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).
A. Zosel: Effect of cross-linking on tack and peel strength of polymers. J. Adhes. 34 (1–4), 201 (1991).
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).
K. Kremer and G.S. Grest: Dynamics of entangled linear polymer melts — A molecular-dynamics simulation. J. Chem. Phys. 92 (8), 5057 (1990).
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).
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).
M.J. Stevens: Manipulating connectivity to control fracture in network polymer adhesives. Macromolecules 34 (5), 1411 (2001).
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).
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).
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).
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).
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).
S. Plimpton: Fast parallel algorithms for short-range molecular-dynamics. J. Comput. Phys. 117 (1), 1 (1995).
W. Humphrey, A. Dalke, and K. Schulten: VMD: Visual molecular dynamics. J. Mol. Graph. 14 (1), 33 (1996).
G. Marsagli: Choosing a point from surface of a sphere. Ann. Math. Stat. 43 (2), 645 (1972).
We acknowledge support from Henkel Corporation. We acknowledge fruitful discussions with M. Hamm, C. Paul, and P. Palasz.
About this article
Cite this article
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