Using the peel test to measure the work of adhesion in a confined elastic film

Diagram of a cantilever plate experiment. A thin elastomeric film is bonded to a rigid substrate and a flexible glass plate is peeled away from it by inserting a spacer of height ∆ between the plate and the film. The distance a between the spacer and the edge of the crack can be used to quantify the bonding strength of the adhesive.

The authors present theoretical and experimental work in an effort to characterize the strength of adhesion forces between a thin elastomeric film bonded to a rigid surface and a flexible plate. The peel test is used to measure the adhesive forces: a spacer of known height is slipped between the flexible plate and the rigid surface, such that a crack forms between the adhesive and the flexible plate. The height of the spacer ($\Delta$) and the length of the crack (a) are used with other parameters to quantify the strength of the adhesive force, as a stronger adhesive should correspond to a shorter crack. The authors examine the limits of perfect adhesion and of perfect slippage in this analysis.

General Information

Keywords: surface force, peel test, adhesion

Authors: Animangsu Ghatak, L. Mahadevan, and Manoj K. Chaudhury.

Date: June 19, 2004.

Department of Chemical Engineering, Lehigh University, Bethlehem, Pennsylvania 18015

Division of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138

Langmuir 21, 1277-81. [1]

Summary

The authors first develop a theoretical framework for analyzing the adhesion strength of a thin elastomer film in terms of the length of the crack that is formed by a spacer in the peel test. Arguments are made based on boundary conditions in terms of incompressibility as well as continuity and smoothness of the displacement vector field of the coverslip, or flexible glass plate. The result of the theoretical analysis is:

$\frac{\Delta D^{1/2} k^2}{\gamma^{1/2}} = ({\frac{W}{12 \gamma}})^{1/2} f_1 (ak)$

where $\gamma$ is the surface energy of the films, W is the work of adhesion, D is the bending stiffness, $f_1$ is a complicated function that comes out of the theory with imposed boundary conditions, and k is a characteristic length scale of the deformable plate.