The mechanics of adhesion have been investigated both theoretically and experimentally, using model adhesive joints consisting of a crosslinked amorphous rubber bonded to a variety of rigid polymeric substrates.
An adhesive failure energy, θ, is defined which is characteristic of the bond but independent of test-piece geometry. Both theory and experiment show that θ has the form, θ=θ0f(R) where θ0 is the “intrinsic adhesive failure energy” which depends only on the physical and chemical nature of the adhesive-substrate interface, and f is a function of R, the “reduced” rate of failure propagation obtained from rate and temperature data using the WLF equation.
θ0 is the work of bond fracture across the interface and, for clean interfacial failure, is equal to the thermodynamic work of adhesion wA. Where failure is not purely interfacial, θ0 can be expressed as θ0=iI+r0+sF where i, r, and s are respectively the area fractions of interfacial, cohesive-in-rubber and cohesive-in-substrate failure, and I, θ0, and F are the intrinsic failure energies for the interface, rubber, and substrate, respectively.
It is believed that this work is the first to demonstrate explicitly and quantitatively the separate contributions of interfacial properties and bulk rheological behavior to the strength of adhesive joints.
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