Liquid lubrication may provide a solution to\nthe problem of high friction and wear in micro-electromechanical\nsystems. Although the effectiveness of this\napproach has been demonstrated in laboratory-based friction\ntests, practical constraints prevent it from being applied\nin commercial devices. The main problem is how to\nposition the lubricant on a silicon surface in order to limit\nspreading and evaporation. This paper describes two\ntechniques to address this issue. First, low concentrations\nof additives are used to promote autophobic behaviour.\nTests� results show that certain concentrations of both\nmultiply alkylated cyclopentane and amine additives are\neffective in halting the spread of hexadecane on silicon,\nand, in the latter case, cause the hexadecane drop to subsequently\nretract. The second approach involves applying a\nmicro-contact printing technique previously used on gold\nsurfaces. Here, silicon surfaces are coated with octadecyltrichlorosilane\nmono-layers that are then selectively removed,\nusing oxygen plasma, to leave regions of\ncontrasting surface energy. Results from spin tests show\nthat surfaces treated in this way can anchor 1 ll drops of\nhexadecane and water when forces of up to 22 and 230 lN,\nrespectively, are applied.
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