Project Objectives

SSLiP has four headline objectives handled by five work packages (WP) across a three-stage of reporting. These objectives while challenging are plausible: The developments proposed in SSLiP are founded in experimental and theoretical advances from the last decade within the fields of granular physics, 2D material synthesis and control including active tribochemical surface re-generation, cutting-edge colloidal visualization, and nano/micromechanical testing. Together, these will realize network building blocks with necessary tribological properties. The team and infrastructure assembled are world-class leaders selected to have the skills and experience required to tackle these objectives

Objective 1: Superlubric network structural elements

SSLiP structural elements must provide robust superlubricious exterior function as well as internal load bearing strength during sliding. To achieve our goals, we employ two approaches. The first involves surface patterning of diamond-like carbon (DLC) and silicon wafer to create micro asperities, functionalized with 2D materials like graphene and MoS2 using mechanical shearing (penciling) or deposition methods such as CVD or liquid phase exfoliation (Left SEM image, 5 micron pitch DLC grits). The second approach entails synthesizing core-shell tribocolloids with core colloids of varying materials, coated with 2D materials using wet chemical coating, CVD, or thermal conversion processes to optimize hardness and thermal conductivity, safeguarding the colloids from damage (right SEM image; Pyrolithic carbon coated 5 micron SiO2 spheres).

Objective 2: Single contact superlubricity

TCD will use a 3D-nanoindentation system (left image) to characterize the contacts made with SSLiP mesoscale structural elements and tribochemistry (WP3). This unique system will explore tribochemical regeneration the regime of high pressure (10 MPa to GPa) and reciprocating sliding speeds (um/s to cm/s) under ambient and liquid (glycerol etc.) conditions provided by ECL. Supporting experiments, NTNU will perform molecular dynamics (MD) simulations of single-contacts drawing on extensive theoretical experience with nanotribology. In addition, microscopic understanding of the tribochemical processes, leading to materials rejuvenation, will be modelled with first-principles methods by TCD. Thermodynamical information, namely the enthalpy of reaction along the possible different reaction paths and the associated reaction barriers, will be extracted from density functional theory (DFT) calculations.

Objective 3: The superlubricious contact network

The core of SSLiP is designing mesoscale structural elements, combining tribocolloids and surface tribomesostructures to ensure superlubricity persistence in macroscopic sliding interfaces. The network supports normal load and undergoes restructuring during sliding, creating an exceptional shear zone. Understanding how superlubricious tribocolloids interact and behave collectively in multi-contact interfaces is vital. Direct visualization of the network will be conducted in rheology experiments at UvA, while simulations at PoliMi and NTNU will explore the influence of various parameters and compare results to experiments. These simulations will be linked to single-contact scale simulations. Additionally, ECL will investigate the self-healing tribochemistry of the contact network.

Objective 4: Macroscale superlubricant system

SSLiP will deliver a demonstrator for replicating wear and friction conditions across various scales and loads relevant to industrial applications. Combining macro- and meso-scale models with large-scale molecular dynamics using machine-learning force fields will yield the ideal materials parameters. This comprehensive multi-scale approach will provide a powerful designing tool for tribo-colloidal systems.