Abstract
Taking advantage of the strong charge interactions between negatively charged graphene oxide (GO) sheets and positively charged poly(diallyldimethylammonium chloride) (PDDA), self-assembled multilayer films of (GO/PDDA)n were created on hydroxylated silicon substrates by alternating electrostatic adsorption of GO and PDDA. The formation and structure of the films were analyzed by means of water contact angle measurement, thickness measurement, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). Meanwhile, tribological behaviors in micro- and macro- scale were investigated by AFM and a ball-on-plate tribometer, respectively. The results showed that (GO/PDDA)n multilayer films exhibited excellent friction-reducing and anti-wear abilities in both micro- and macro-scale, which was ascribed to the special structure in (GO/PDDA)n multilayer films, namely, a well-stacked GO–GO layered structure and an elastic 3D crystal stack in whole. Such a film structure is suitable for design molecular lubricants for MEMS and other microdevices.
Highlights
The advances in micro-nano manufacturing technology have promoted the rapid development of microelectronic mechanical systems (MEMS) and micro/nanodevices
We focus on the tribological behaviors of (GO/ poly(diallyldimethylammonium chloride) (PDDA))n multilayers in micro- and macro-scales
Negatively charged graphene oxide (GO) layer was modified by electrostatic adsorption of positively charged PDDA
Summary
The advances in micro-nano manufacturing technology have promoted the rapid development of microelectronic mechanical systems (MEMS) and micro/nanodevices. Low friction, and high chemical stability, graphene is expected to reduce the adhesion, friction, and wear problems of MEMS as a solid lubricant (Lee et al, 2008; Popov et al, 2013; Berman et al, 2014). 2D GO nanosheets with negative charge and PDDA with positive charge were employed to construct mechanically stable (GO/PDDA)n multilayer films by a layer-by-layer (LBL) self-assembly method. The combination of elastically strong PDDA and mechanically strong 2D GO nanosheets is expected to boost high loading capacity and anti-wear life, aiming at developing thin-film lubricants suitable for MEMS and micro/nanodevices. GO SAM covered Si wafers were kept in the PDDA water solution (1.5 wt%) for 1 h, followed by washing with ultrapure water and drying in N2 gas. All tests were made under ambient conditions of 20°C and 40%–50% relative humidity
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