About the project
The overall strength of granular materials and porous rocks is often associated with processes that take place in fluid-filled contacts between individual solid grains. To recognize these processes and to be able to modify them, we need analytical methods that investigate the relevant interfaces at a nanoscale. In this experimental project, we study the interfaces with the Surface Forces Apparatus (SFA).
SFA measures surface forces acting at nanoscale surface separations between two macroscopic surfaces (a contact radius diameter is approximately 100 µm). An in-situ sensing SFA modification developed by the Applied Interface Physics group at the Vienna University of Technology allows monitoring of the measured forces in real-time, owing to the addition of strain gage-based force-measuring sensors. That expands the applications of the SFA and enables force measurements without bringing the surfaces out of contact. Owing to the use of the white light interferometry technique coupled to the SFA, we can also simultaneously visualize recrystallization, dissolution, and growth of the two confining surfaces.
Objectives
The overarching goal of this project is to recognize which processes make the interfaces weak, and how to convert the weak interfaces into strong ones. Although we see destructive effects of weak interfaces at a macroscopic scale (earthquakes, rock compaction and subsidence, and general material failure), the very mechanisms governing the interfacial strength are frequently operating at much smaller scales (10-9 m). The SFA technique lets us probe various nanoscale processes occurring between two confined solid surfaces and assess what impacts the interfacial strength the most.
Outcomes
In the first year of this project, we focused on the very composition of confined solid-solid interfaces filled with electrolytes or organic solutions. We showed that the biding of soluble organic molecules could be modulated by the addition of inorganic ions, which have a different affinity to both adsorb onto the solid confining walls and to form complexes with the functional groups of the organics. Using the electrochemical SFA (EC-SFA), we further studied the transport of organic and inorganic ions into and out of a nano-sized confined gap. With the EC-SFA, we can rapidly change the surface charge of one of the confining surfaces and visualize how the ions are transported. In this work, we observed a number of interesting metastable charge regulation pathways emerging before the charge equilibrium is achieved in a nano-sized gap between two solid surfaces.
Read more updates from the project here!
Financing
The Research Council of Norway, FRIPRO Mobility Grant
Cooperation
- The Njord Center, University of Oslo, Norway
- Vienna University of Techonology, Vienna, Austria
