Synthesis of two-dimensional WS2/nickel nanocomposites via electroforming for high-performance micro/nano mould tools

Abstract

To reduce the adhesion and friction between polymer and mould surfaces during polymeric micro/nano structures replication, we have used tungsten disulfide (WS2) nanosheets to fabricate high-performance nickel/WS2 nanocomposite mould using electroforming. However, the aggregation of WS2 nanosheets in the electroforming solution is a critical issue that influences the mechanical and tribological properties of the mould. In this study, we first propose a new strategy of combining anionic surfactant sodium dodecyl sulfate (SDS) and cationic surfactant cetyltrimethylammonium bromide (CTAB) to achieve uniform dispersion and incorporation of WS2 nanosheets in the electroformed nickel mould. Our results indicate that appropriately designing the structure of CTAB-SDS complex can achieve a stable WS2 dispersion, contributing to the uniform co-deposition of WS2 nanosheets into nickel mould. The combination of high concentration of CTAB and SDS (1.0 g/L CTAB and 1.0 g/L SDS) significantly improved the dispersibility and incorporation of WS2 into the nickel matrix, compared to individual SDS or CTAB. Consequently, the maximum hardness enhanced by 350% from 284 HV for pure nickel to 1280 HV for nickel/WS2 nanocomposite mould, along with the coefficient of friction (COF) against the polymethyl methacrylate (PMMA) pin reducing from 0.75 to 0.31. It is also found that CTAB promotes particle encapsulation while SDS improves the particle dispersion but cannot control the particle incorporation. The surface wettability of nickel/WS2 mould altered to hydrophobicity from hydrophilicity of nickel mould, where the adhesion-induced wear caused by polymer pin significantly reduced. Moreover, the surface roughness did not change much with the incorporation of WS2 into the mould, which is acceptable for mould applications. Finally, the nickel/WS2 nanocomposite mould was successfully fabricated via electroforming and its self-lubricating properties was validated by micro hot embossing PMMA microfluidic chips with good surface quality.