Layer by layer assembled functionalized graphene oxide-based polymer brushes for superlubricity on steel–steel tribocontact. Issue 29 (12th July 2021)

• Record Type: Journal Article
• Authors: Samanta, Suprakash; Sahoo, Rashmi R.
• Is Part Of: Soft matter. Volume 17:Issue 29(2021)
• Page Start: 7014
• Page End: 7031
• Publication Date: 2021-07-12
• Subjects: Soft condensed matter -- Periodicals; 530.413
• DOI: 10.1039/d1sm00690h
• Languages: English
• ISSNs: 1744-683X

Abstract

Abstract : Tribological behavior of graphene-based polymer brushes (Gr-PB) in lube oil is investigated. Gr-PB reduce COF and the wear of steel–steel tribocontact in variable pressure conditions aided by the formation of robust tribofilm in sliding interface. Abstract : This study demonstrates a simple and multistep approach for a covalent functionalization of chemically-prepared graphene oxide (GO) using branched polyethylenimine (PEI) through nucleophilic addition reaction to prepare GO-PEI. Further layer-by-layer (LBL) assembly on functionalized GO-PEI with anionic polyelectrolyte, poly(acrylic acid sodium salt) (PAA) and poly(sodium 4-styrenesulfonate) (PSS) have been undertaken to fabricate polymer brushes (PB). The physicochemical structures of GO, GO-PEI and LBL assembled PB [GO-PEI-PAA and GO-PEI-PSS] have been explored using standard spectral and morphological analysis. The macrotribological results demonstrated that GO-PEI-PAA/GO-PEI-PSS (0.5 wt%) as paraffin oil dispersible additives significantly decreased the coefficient of friction (COF) and wear at different contact pressures of steel–steel tribopairs. The influence of contact pressure and load-bearing ability of the polymer-grafted GO as nanolubricants have been examined carefully. The COF of PB particles provided a reduction of 85% (low pressure, ∼0.9 MPa) and 66.65% (high pressure, ∼1.35 GPa) compared to lube paraffin oil and exhibited a lower specific wear rate (2.26 × 10 −8 mm 3 N −1 m −1 ) at macrotribological pin/ball-on-disc trials, revealing superior lubricity. The PB containing nanolubricants also exhibited high load-bearing ability (till ∼1000 N load, P m ∼6.1 GPa) with considerably lower COF and wear, which were investigated using a four-ball tribotester. Among the functionalized polymeric GO particles, PSS polyelectrolyte containing GO-PEI-PSS showed better COF and wear reduction ability with extremely high load-bearing capacity due to the strong interfacial adhesion properties of PSS to generate strong protective synergetic lubricating tribofilm into the rubbing interfaces, which is comprehensively investigated by post-tribological analysis.