Preparation And Tribological Properties Of Silane Mixed Self-assembled Monolayers

With the showed advantages in solving micro friction and wear of MEMS andNEMS, the SAMs technique has become one of the most focused areas. Among silaneSAMs, in which form silicon substrate by organosilane molecular silane, has been themost promising surface modification of materials. In this work, the preparation andtribological properties of silane mixed self-assembled monolayers has beenexperimentally studied.Direct to the shortage existing in the construction and cohesive strength of silanesingle SAMs, APS-WD-10mixed SAMs were prepared through stepwise method I,stepwise method II and eoadsorption method, based on the preparation of silane singleSAMs. The assemble process of mixed SAMs through three alternate methods werecharacterized by X-ray photoelectron spectroscopy (XPS) and atomic forcemicroscopy (AFM), the assembly mechanism was analyzed and the comparison of theresults showed that the eoadsorption method has more advantages in mixed SAMspreparation.Mixed SAMs could react with hydroxylated silicon substrate without the aid ofexternal conditions by thermodynamic calculation. By the integral transformation andMaxwell relations, the surface tension and surface energy were derived, which furtherproved that the reaction was spontaneous. By analyzing the stereospecific blockadehenomenon in the mixed dsorption process of APS atoms and WD-10atoms, theWD-10atoms could insert to the APS atoms, which formed perfect APS-WD-10mixed SAMs.The simulated system of APS-WD-10mixed SAMs was built on the condition ofCOMPASS force field using molecular dynamics simulation software MaterialsStudios, the system’s energy and construction in the assembly process were studyed,the result showed that the result showed that the assembly process was spontaneous.The friction and wear behaviors of mixed SAMs under macro condition wereexperimentally studied using UMT. The friction coefficient of APS-WD-10mixedSAMs were discussed at different load and sliding speed, the result showed that themixed SAMs had superior tribological characteristics, such as low friction coefficientand long destroyed monolayers time.The friction and wear behaviors of mixed SAMs under micro condition wereexperimentally studied using AFM. The surface adhesion and friction force of mixed SAMs were discussed at different load and sliding speed, which showed that thesurface adhesion and friction force of mixed SAMs increased as load and slidingspeed increased, but the amplitude was less than both of single SAMs obviously.