Adhesion of Soft Materials to Rough Surfaces: Experimental Studies, Statistical Analysis and Modelling

Abstract

Adhesion between rough surfaces is an active field of research where both experimental studies and theoretical modelling are used. However, it is rather difficult to conduct precise experimental evaluations of adhesive properties of the so-called anti-adhesive materials. Hence, it was suggested earlier by Purtov et al. (2013) to prepare epoxy resin replicas of surfaces having different topography and conduct depth-sensing indentation of the samples using a micro-force tester with a spherical smooth probe made of the compliant polydimethylsiloxane polymer in order to compare values of the force of adhesion to the surfaces. Surprising experimental observations were obtained in which a surface having very small roughness showed the greater value of the force of adhesion than the value for a replica of smooth surface. A plausible explanation of the data was given suggesting that these rough surfaces had full adhesive contact and their true contact area is greater than the area for a smooth surface, while the surfaces with higher values of roughness do not have full contact. Here, the experimental results of surface topography measurements and the statistical analysis of the data are presented. Several modern tests of normality used showed that the height distribution of the surfaces under investigation is normal (Gaussian) and hence the classic statistical models of adhesive contact between rough surfaces may formally be used. Employing one of the Galanov (2011) models of adhesive contact between rough surfaces, the plausible explanation of the experimental observations has been confirmed and theoretically justified.

Adhesive Strength of Contacts of Rough Spheres

“…They used the Lennard-Jones potential for calculating van der Waals forces between elements (Medina and Dini, 2014). Recently an indentation test of spheres with microforce tester showed that the highest pull-off force was found not on the smooth sample but that with micro roughness (Pepelyshev et al, 2018). It was argued that the increase of the contact area is the main cause for the increase pull-off force.…”

Roughness of Deposited Carbon-Based Coatings and Its Statistical Characteristics at Nano and Microscales

“…Indeed, as it follows from Tables 1, 2, the R rms measured by AFM was below 1.5 nm for the biased a-C sample and below 10.5 nm for the non-biased a-C sample. As it has been recently shown for such small roughness (Pepelyshev et al 2018), a soft counterpart surface may create a full contact. Hence, in such problems only the microscale roughness will govern the contact.…”

“…The main methods for testing for normality are the following tests: Kolmogorov-Smirnov (KS), Lilliefors (LF), Shapiro-Wilk (SW), Anderson-Darling (AD), Cramervon Mises (CVM), the Pearson, and Shapiro-Francia (SF). These tests were already used for checking normality of grinding surfaces (Borodich et al, 2016) and surfaces of replicas of polishing paper samples (Pepelyshev et al, 2018). Here we will present the tests for the sake of completeness.…”

“…Thus, if it is established that the surface roughness is Gaussian, then one can use the classic models of contact. Very recently, we tested the hypothesis of normality using mathematically rigorous approach (Borodich et al, 2016;Pepelyshev et al, 2018) on grinded surfaces. We showed that the asperities of grinding surfaces are not normal at both nano and microscales whilst intact surfaces of replicas of polishing papers are normal.…”

Depth-Sensing Indentation as a Micro- and Nanomechanical Approach to Characterisation of Mechanical Properties of Soft, Biological, and Biomimetic Materials

“…We also need to underline the importance of surface roughness and consideration of related changes in real contact area that can affect adhesion. Experiments of Purtov et al [15] and modelling of the experiments by Pepelyshev et al [16], employing Galanov's model of adhesion between rough surfaces [17], showed that consideration of real contact area is a very important factor in adhesive contact problems. This statement is also nicely confirmed by the analysis of nanoscale static friction by Polyakov et al [18], and various works that demonstrate the influence of roughness on the value of adhesive pull-off force (e.g., [19][20][21]).…”