Role of Preload in Adhesion of Rough Surfaces

Adhesion between glass and bromobutyl and polydimethylsiloxane elastomers is investigated. We show that viscoelastic energy dissipation close to the opening (or closing) crack tip, and surface roughness, strongly affect the work of adhesion. We observe strong adhesion hysteresis and we show, in contrast to the Johnson-Kendall-Roberts theory prediction for elastic solids, that this results in a pull-off force, and effective work of adhesion to be dependent on the maximum loading force.

Figure 1

The experimental set up for measuring adhesion.

Figure 2

A rigid ball pulled away from a viscoelastic solid. A part of the energy needed to remove the ball is derived from the viscoelastic energy dissipation inside the rubber close to the opening crack tip (red dashed region).

Figure 3

(a) Schematic picture of the macroscopic contact area during loading, and (b) during unloading when strong adhesion hysteresis occurs so that $w(v)\gg \mathrm{\Delta }\gamma$. The black regions indicate asperity contact regions. Because of the adhesive interaction, complete contact occurs within the black regions. During pull off in the case of strong adhesion hysteresis, the size of the asperity contact regions remains unchanged (in spite of the reduction in the contact pressure) except close to the macroscopic (apparent) opening crack tip (dashed circle), where the asperity contact regions are broken by the propagation of microscopic opening cracks at each asperity contact region.

Figure 4

(a) The interaction force between the bromobutyl rubber and the glass ball for two different loading situations (thin and thick solid lines), as a function of time. The glass ball approach and retraction velocity $v_z=\pm 25\mu \mathrm{m}/\mathrm{s}$. (b) Filled squares: the pull-off force $F_{\text{pull}\text{−}\text{off}}$, as a function of the maximum loading force $F_m$, for bromobutyl rubber (read squares) and for PDMS (green squares). The open red squares is the pull-off force $F_{\text{pull}\text{−}\text{off}}$ divided by $F_m^{1/3}$ for bromobutyl rubber, as a function of $F_m$. For a glass ball with diameter $2R=4\mathrm{cm}$.