Bonding of a viscoelastic periodic rough surface to a rigid layer

A theoretical analysis is performed for the study of the bonding of a viscoelastic rough surface to a rigid substrate. The mechanics of contact and adhesion are studied with the Dugdale–Barenblatt model for surface interaction. Exact solutions are obtained for arbitrary surface profiles and loading histories. Detailed solutions are given for a power‐law viscoelastic material. This solution is used to determine the time for the self‐bonding of surfaces (solid sintering under zero load). The time to self‐bonding is shown to be extremely sensitive to the aspect ratio of the asperities. A closed form expression is derived for the time needed to achieve full contact when the surfaces are compressed with a load that increases linearly with time. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 545–561, 2002; DOI 10.1002/polb.10113     

Molecular and nanoscale factors governing pressure‐sensitive adhesion strength of viscoelastic polymers

Pressure‐sensitive adhesives (PSAs) are finding increasing applications in various areas of industry and medicine. PSAs are a special class of viscoelastic polymers that form strong adhesive joints with substrates of varying chemical nature under application of light external bonding pressures (1–10 Pa) over short periods of time (1–5 s). To be a PSA, a polymer should possess both high fluidity under applied bonding pressure, to form good adhesive contact, and high cohesive strength and elasticity, which are necessary for resistance to debonding stresses and for dissipation of mechanical energy at the stage of adhesive bond failure under detaching force. For rational design of novel PSAs, molecular insight into mechanisms of their adhesive behavior is necessary. As shown in this review, strength of PSA adhesive joints is controlled by a combination of diffusion, viscoelastic, and relaxation mechanisms. At the molecular level, strong adhesion is the result of a narrow balance between two generally conflicting properties: high cohesive strength and large free volume. These conflicting properties are difficult to combine in a single polymer material. Individually, high cohesive interaction energy and large free volume are necessary but insufficient prerequisites for PSA strength. Evident correlations are observed between the adhesive bond strengths of different PSAs, and their relaxation behaviors are described by longer relaxation times. Innovative PSAs with tailored properties can be produced by physical mixing of nonadhesive long‐ and short‐chain linear parent polymers, with groups at the two ends of the short chains complementary to the functional groups in the recurring units of the long chains. Although chemical composition and molecular structure of such innovative adhesives are unrelated to those of conventional PSAs, their mechanical properties and adhesive behaviors obey the same general laws, such as the Dahlquist's criterion of tack. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

The mechanics of contact and adhesion of periodically rough surfaces

An analytical model based on the Johnson–Kendall–Roberts (JKR) theory of adhesion was used to study the contact mechanics and adhesion of periodically rough surfaces. The relation of the applied load to the contact area and the work of adhesion W was found in closed form for arbitrary surface profiles. Our analysis showed that when the parameter [where α* is a numerical constant of order one, β is the aspect ratio of a typical surface profile (or asperity), and ρ is the number of asperities per unit length], the surfaces will jump into contact with each other with no applied load, and the contact area will continue to expand until the two surfaces are in full contact. The theory was then extended to the non‐JKR regime in which the region where the surface forces act is no longer confined to a small region near the contact zone. Exact solution was also obtained for this case. An exact analysis of the effect of entrapped air on the mechanics of adhesion and contact was also enacted. The results showed that interaction between asperities should be taken into consideration in contact‐mechanics models of adhesion or friction. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 1195–1214, 2001