Confining Liquids on Silicon Surfaces to Lubricate MEMS

Abstract

Liquid lubrication may provide a solution to the problem of high friction and wear in micro-electromechanical systems. Although the effectiveness of this approach has been demonstrated in laboratory-based friction tests, practical constraints prevent it from being applied in commercial devices. The main problem is how to position the lubricant on a silicon surface in order to limit spreading and evaporation. This paper describes two techniques to address this issue. First, low concentrations of additives are used to promote autophobic behaviour. Tests' results show that certain concentrations of both multiply alkylated cyclopentane and amine additives are effective in halting the spread of hexadecane on silicon, and, in the latter case, cause the hexadecane drop to subsequently retract. The second approach involves applying a micro-contact printing technique previously used on gold surfaces. Here, silicon surfaces are coated with octadecyltrichlorosilane mono-layers that are then selectively removed, using oxygen plasma, to leave regions of contrasting surface energy. Results from spin tests show that surfaces treated in this way can anchor 1 ll drops of hexadecane and water when forces of up to 22 and 230 lN, respectively, are applied.

Effects of beverage carbonation on lubrication mechanisms and mouthfeel

“… FSurface_Adhesion is the traction exerted by the sliding PDMS surface on the contact line. This is a complex function as the contact angle varies around the bubbles' circumference but can be estimated, according to [33,37,38] from FSurface Adhesion ≈ 2lγ(cos θr -cos θa) where l is the diameter of the bubble, γ is the surface tension and θa and θr are the advancing and receding contact angles respectively. For the bubble geometry in Figure 7, this force is ~ 40 µN and, due to the sliding motion, it always acts in the positive/downstream direction (see Supporting Information 2.4).…”

Molecular Interactions between Ionic Liquid Lubricants and Silica Surfaces: An MD Simulation Study

“…In particular, ILs appear to be adequate lubricants of micro/nano-electromechanical systems (MEMS/NEMS) involving moving parts. Lubrication of these miniaturized devices has been the focus of intense research work in the last two decades − because their large surface-to-volume ratios demand lubricants of high performance to avoid serious adhesion and friction problems. Various families of ILs based on the cations imidazolium, phosphonium, ammonium, pyrrolidinium, pyridinium, and guanidinium have been tested, both as neat lubricants or additives, in the lubrication of the silicon contacts, which mimic the behavior of MEMS and NEMS. − The most successful anions were those containing sulfur-based functional groups. , …”