In this study, we show that magnetic particle spectroscopy can be used to monitor the formation of coffee rings in ferrofluid droplets in real time. We attribute this to the change in magnetization response of the magnetic nanoparticles as they form a dense coffee ring deposit due to increased interparticle dipolar interactions.
Kämäräinen T.*, Heinlein M., Luthardt L., Wolf A., Mandel K.*
Magnetic particle spectroscopy analysis of the coffee ring effect in sessile ferrofluid droplets
In: Journal of Colloid and Interface Science (2026), just accepted