Macroscale Light-Controlled Lubrication Enabled by Introducing Diarylethene Molecules in a Nanoconfinement

Abstract

Reversible friction regulation is of long-standing great interest in the fields of both industry and scientific research, so some materials and theories have been developed aiming to solve this problem. Light-sensitive materials are promising because of the easy controllable switching of the properties and structures. Here, a reversible light-controlled macrolubrication was realized by regulating the performance of nanoscale light-sensitive molecules adsorbed on contact surfaces. In this work, symmetric diarylethene and asymmetric diarylethene had been designed and synthesized as functional materials. The friction forces were found to be obviously increased upon exposure to ultraviolet light and decayed to the initial value under visible light. In addition, the friction coefficient changed alternately with ultraviolet and visible illumination. According to the results of experiments and simulation of material properties, the behavior was suggested to be attributed to the difference in shear stiffness of the nanoscale diarylethene molecule adsorption layer triggered by two wavelength lights. This work not only provides a new lubrication regulation technology but also develops intelligent engineering materials.

Photorheological fluids of azobenzene polymers for lubrication regulation

“…5(d). The COF change ranges were 20%-100% in other works of light-induced friction [5,55,56]. Further studies of light-controlled friction fatigue tests showed that the friction regulations underwent reversible transformation under UV and NIR light, as shown in Fig.…”

“…The viscosity of fluids is closely tied to industrial production and daily life, such as in navigation [1,2], pipe flows [3], mechanical lubricants [4][5][6][7][8][9][10][11], water conservancy, and biorheology [12,13]. In particular, with the development of intelligent fluids such as electrorheological fluids [14,15], magnetorheological fluids [16][17][18][19][20], pH-sensitive fluids [21], photorheological fluids [22][23][24], and other stimuli-responsive fluids [25,26], these intelligent fluids are attracting extensive attention as smart fluid dampers for vehicle [27,28], oil and gas pipeline transportation [29], in wafer surface polishing [30,31], and friction regulation [5,[32][33][34][35][36]. However, some intelligent fluids have disadvantages, such as in electrochemical corrosion in electrorheological fluids.…”

Light-Controlled Friction by Carboxylic Azobenzene Molecular Self-Assembly Layers

“…There have been some studies on the tribological properties of the self-assembled organic molecule layers ( Nalluri et al, 2011 ; Shi et al, 2018 ), while the studies on the tribological properties of the photo-regulated molecular layers have been reported rarely ( Pace et al, 2007 ; Tang et al, 2020 ). For the self-assembly layers of the NN4A and NN2A molecules, we had investigated the tribological lateral forces using AFM at room temperature.…”

“…In general, external field regulation is the way that people usually choose, such as light stimulation, electric field, heat, chemicals, etc. ( Zhang et al, 2012 ; Yokoyama et al, 2014 ; Cai et al, 2017 ; Cao et al, 2018 ; Meng et al, 2020 ; Tang et al, 2020 ). Among all possibilities, light is probably utilized to realize intelligent control of photochromic self-assembly due to its remote control, non-invasive, and cleaning properties.…”

Phototribology: Control of Friction by Light

“…Indeed, photorheology is a cutting-edge field where active control of viscosity can be achieved by light . Recently, active control of lubrication by UV–visible illumination of a ball-on-disc tribological system has been reported . Also, the direction of the motion of 3,3′-dimethylazobenzene crystals on a glass surface could be actively controlled by the position of the light sources .…”