Fine Tuning the Adhesive Properties of a Soft Nanostructured Adhesive with Rheological Measurements

Abstract The major objective of this article is to present recent advances in the methodology to fine tune the adhesive performance of a PSA. In addition to the so-called Dahlquist criterion requiring a low modulus, we propose two additional rheological predictors of the adhesive properties. The first one is derived from the description of the detachment of a linear elastic layer from a rigid substrate. We made an approximate extension of this analysis to the viscoelastic regime and showed that the transition from interfacial cracks to cavitation and fibrillation can be quantitatively predicted from the easily measurable ratio tan(δ)/G′(ω). If a fibrillar structure is formed, the nonlinear large strain properties become important. We showed that the ability of the fibrils to be stretched before final debonding can be predicted from the analysis of simple tensile tests. The softening, which occurs at intermediate strains, and, more importantly, the hardening which occurs at large strains, can be used to predict the mode of failure and the energy of adhesion. The use of this methodology to tune the PSA structure for a specific application has been illustrated for the special case of wb-PSA made of core-shell particles, and improved adhesive properties on polyethylene surfaces have been obtained. Keywords: Adhesion predictorsLinear viscoelastic propertiesMicrostructure-property relationshipNonlinear elasticityPSA ACKNOWLEDGMENTS The authors would like to thank all the collaborators of the "Designed Nanoscale Heterogeneities for Controlling Waterborne Pressure-Sensitive-Adhesive Performance" (NsHAPe) project funded by the European Commission Sixth Framework Program (Contract No. NMP3-CT-2004-505442). We would like specifically to thank C. Lei from the University of Surrey for the AFM image of Figure 9. Notes 1Shell and core T gs are calculated using the Fox equation. 2The final T g of the adhesive film is measured by differential scanning calorimetry at a heating rate of 10°C/min. 3Value not reported here since it is Cytec proprietary information. 1 T gs are calculated using the Fox equation. a Cohesive transfer, i.e., most of the adhesive remains on the adherend and is transferred from the backing. b Cohesive failure, i.e., adhesive remains on the steel and on the backing.