Adhesion Of Rough Surface With Specified Statistical Parameters

Adhesion has a very significant impact on micro and nano-electromechanical systems, scanning probe microscopy, nano-manipulation, nano tribology, nano-wear, and some other related fields. It is a big problem in micro/nano engineering to accurately predict adhesion and control it that we can avoid the adverse adhesion, use the good adhesion effectively.The real surface is not ideal smooth, and its surface micro-/nano-structures are of critical importance due to their adhesive performances. For in-depth understanding of the intrinsic interdependences in a more quantitative manner, fabrications of three-dimensional (3D) surface structures with precisely controlled statistical parameters are highly demanded.Toward the purpose of understanding the adhesion of surfaces with precisely controlled statistical parameters, roughness surfaces were designed, fabricated and reproduced and their surface adhesion properties were characterized and analyzied. The following investigations have been performed:1. Design of3D specimens with controllable roughness parameters. Engineering surfaces manufactured by an abrasive process like grinding may have higher correlation lengths. In order to improve the design accuracy, especially for the surfaces with higher correlation lengths, and raise the algorithm efficiency, genetic algorithms were introduced into the non-linear conjugate gradient method. The procedures employ either the NCGM or FFT method. The results show that both the FFT methods can adequately produce surfaces at small correlation distances, while at higher correlation distances the NCGM yields better results.2. Fabrication and reproduction of the3D specimens. A set of3D roughness structures with different height distributions and autocorrelation lengths were fabricated by focused ion beam milling on a silicon substrate.The influence of grayscale level in fabrication was investigated.With the increase of the grayscale, the surfaces are smoother. The measured results and the designed templates were compared quantitatively. Results demonstrated that they are generally in close agreements the relative deviations of maily paramters are below10%. The fabricated surfaces with grayscale level of64are most satisfactory as determined from the visual image quality.Then, the rough patterns were reproduced efficiently on polydimethylsiloxane by using direct polymer casting. The mass reproductions of the artifacts can support further roughness-relevant functional performances. The agreements between template and replica were evaluated and compared by an atomic force microscopy. The typical parameters are in well accordance, such as Sq, the relative deviations are within the range from-6.4%to1.7%.It is found that the spectra match well in the low spatial frequency range for each set of template and replica. The3D surface roughness parameters and power spectral density of both the surfaces were analysized. The work can support for the subsequent experiments and quantitative analysis.3. Characterization of the adhesion properties of the3D rough specimens. After accurate calibration of the AFM cantilever spring constant, adhesion measurements using force-distance curves were performed on the roughness specimens. Two probes were adopted, including a common probe and a colloidal probe. Then, finite element analysis was used to elucidate the adhesive properties between a colloidal sphere and a rough surface. Simulation results show that the contact area increases gradually with the increase of the correlation length. The experimental and simulation results will be helpful to build a good foundation for exploring the relation between the roughness parameters and the adhesion, predicting of the adhesion force.