Nanotribology (atomic-scale friction)
Friction is a phenomenon encountered in everyday life, where two surfaces come into contact and move with respect to each other. Together with adhesion, wear and other interfacial interaction also known as tribology, friction has been a major theme of interest for hundreds of years, both from practical and fundamental perspectives. We use Atomic Force Microscopy (AFM) that can monitor friction in the single-asperity level with a technique termed Friction Force microscopy (FFM), to detect details down to the sub-molecular scale. This is achieved through the interaction between a sharp AFM cantilever tip and a surface, where lateral forces are measured during the relative motion between them. We use this information to study fundamental contact behavior during nanoscale friction in liquid and ambient surroundings.
Single molecule force spectroscopy
In recent years single molecule force spectroscopy techniques have evolved considerably, becoming an important approach in addition to traditional bulk methods. While ensemble bulk measurements study the averaged properties of a system, single molecule measurements illuminate the tails of these properties’ distributions. A single macromolecule (such as polyproteins) can be held and manipulated with an AFM apparatus, which has the ability to detect subtle details at sub-nanometer resolution, and explore a its mechanical response and dynamical behavior (such as unfolding, collapsing and refolding) by measuring a wide spectrum of forces ranging from a few to thousands of pico-Newtons. The single protein recorded force traces disclose its mechanistic features, such as reaction rates, diffusion coefficients, unfolding/refolding dynamics, free-energy landscapes available to perform work and conformational transition.
We employ nanoindentation and contact-adhesion measurements using AFM to study the nano- and meso-scale mechanical properties of surfaces, and the contact interaction between materials. Capturing atomic-scale interactions is important for fundamental research and technological applications. These interactions are manifested through adhesion work, which can be evaluated by direct measurement of adhesion (pull-off) forces. Besides the knowledge on the adhesive interaction between surfaces, such measurements can provide information on the elastic (Young modulus) and viscoelastic nature (nanoindentation). We apply this technique to study the interaction and mechanical properties of both hard (solids) and soft (hydrogels and biofilms).