Determination of the viscoelastic interfacial properties between silica and SNR-based materials via a semi-empirical approach

• The rubber–silica interface is simulated by rubber indented by a silica tip.
• The experimental data are analyzed using a semi-analytical contact model.
• The values of the localized equivalent creep compliances are determined by eliminating the influence of adhesion between the contact surfaces.
• The values of work of adhesion between the contact surfaces are obtained.

The properties of the surface and rubber–filler interface of a rubber-based material may be different from those of the bulk. The time-dependent relaxation modulus and creep compliance function of surface can be obtained through an indentation test involving the influences of both localized creep and surface adhesion. This paper reports an approach to obtain localized surface and interfacial properties for synthetic natural rubber (SNR) films by means of a newly developed semi-empirical method. The rubber–silica interface is simulated by rubber indented by a silica tip. The SNR films with several different crosslink densities were prepared utilizing the solution casting method. Indentation tests were performed following a step loading-holding and a ramp loading-holding–unloading procedure. Fused silica balls of 500 μm radius were used as tips in the experiments. The indentation time, penetration depth, and applied load data were recorded during each test. The localized creep compliance and work of adhesion between the tip material and the rubber surface were obtained, using the semi-empirical method, from the experimental data. The results show an inverse relationship between the crosslinking density of the SNR and the creep compliance. The same trend is also found in the work of adhesion, which is defined based on the Dugdale cohesive zone model for describing the interface between the silica tip and the SNR sample surface.