Academic Awards 2025 booklet

83 Towards NMR Imaging of Ink Penetration in Paper Modern printing relies on two essential components: paper and ink. To enhance print quality and sustainability, a deeper understanding of how liquids and particles interact with paper is required. Prior to my project, no technique could simultaneously achieve the high spatial and temporal resolution required to study ink penetration in real time. With the fastest NMR imaging ever recorded, my thesis marked a significant breakthrough. This advancement enabled real-time monitoring of ink penetration like never before (see Figure 1). The method combines a GARField NMR setup with a modified pulse sequence, enabling visualization of liquid movement, particle transport, and complex paper deformations. By incorporating iron-oxide into nanoparticles, making them NMR-visible (Figure 2), particles could be tracked and illustrated how concentration influences penetration speed and depth. The study identifies three main regimes in ink penetration: capillary uptake, swelling, and air removal (see Figure 3) and shows how treatments like hydrophobization and compression influence absorption. The unseen time resolution of our technique generated critical data about particles, liquids, and paper deformation, enabling strategies to reduce ink usage, enhance the performance of recycled paper, and support eco-friendly printing. Furthermore, the technique shows potential beyond printing, including water filtration, wearable electronics, and other emerging technologies. Figure 1: Schematic representation of the measurement setup (left) and a typical particle penetration profile (right). Shown are the curved magnetic poles of the GARField NMR, the RF-coil, the syringe and droplet sensor. The sample consists of a droplet, nylon membrane (brown), double sided tape (light grey) and glass plate (dark grey). The liquid within the droplet and membrane is shown in blue and particles are shown with brown circles. The corresponding liquid front l(t) and particle front p(t) are marked with orange and blue line respectively. The same markings are used within the 1D signal profiles. Figure 2: Scanning Transmission Electron Microscopy image of the iron-oxide nanoparticles containing 7.5 wt% iron-oxide. The iron-oxide within the particles can be seen as white spots.