| Adhesion plays a signicant role in micro-or nanoelectromechanical systems (MEMS/NEMS), scanning probe microscope (SPM) measurements, nanomanipulation, nanotribology, nanowear and some other related fields. Due to the very large surface-to-volume ratio, adhesion is one of the major factors that limit the widespread use of MEMS/NEMS, and thus attracts much attention in the community.Adhesion hysteresis is defined as the difference between the work needed to separate two surfaces and that originally gained on bringing them together. Adhesion hysteresis is a common phenomenon in most surface/interface interactions. The first part of this thesis focuses on studying the effects of surface roughness on adhesion hysteresis while the second part does thermodynamic analysis of liquid bridge in AFM, trying to find out the effect of different factors on adhesion hysteresis.Firstly, we assume the surface asperity height distribution is Gaussian. Numerical simulations based on Fuller's model show that adhesion hysteresis depend upon a single dimensionless parameter, adhesion parameter, which represents the statistical average of a competition between the compressive forces exerted by the higher asperities which are trying to separate the surfaces and the adhesion forces between the lower asperities which are trying to hold the surfaces together. Using the Fuller and Tabor analysis, the loading and unloading path was obtained. It is found that adhesion hysteresis is determined by the adhesion parameter, the ration between the dispersion of asperity heights and the elastic extension which an asperity can sustain before it breaks contact with the other surface.Lastly, We use thermodynamics to determine capillary adhesion laws in an extreme cases—constant volume for a general geometrical model (a spheres contacted with a flat substrate, AFM model). Our most important result is that with the drawing of the sphere from the flat substrate, the tempreture of the liquid bridge will be decreased. |
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