Temporally and spatially resolved characterisation of pores in paper with high-resolution fluorescence microscopy

• Applicant: Privatdozent Dr. Tobias Meckel
• Subject Area: Synthesis and Properties of Functional Materials
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 405440040

The interaction of (aqueous) liquids with paper plays a central role in the production, investigation, modification, functionalization and application of paper. This interaction can be divided into different processes, such as (i) wetting and swelling of cellulose fibers, (ii) capillary transport within, on or between fibers, or (iii) accessibility of pores on or between fibers for dissolved or suspended substances of different size, charge or hydrophilicity. The quantitative investigation and description of such individual processes, which always occur simultaneously as soon as the paper comes into contact with liquids, are indispensable to arrive at an understanding of the complex microfluidic properties of paper. Only through this understanding will it be possible to provide paper with tailored properties in a rational and controlled manner. The aim is to detect and quantify the influence of various paper parameters, such as fiber type or chemical functionalization, on the behavior of liquids and the substances dissolved or suspended in them with high spatial and temporal resolution within the paper matrix. An additional focus will be the influence of non-cellulosic polysaccharides. For this purpose, the already established range of methods of fluorescence microscopy will be used, which is particularly suitable for quantitatively recording dynamic processes that take place on very different length and time scales in all three spatial dimensions. In particular, resonance and spinning disk confocal microscopy have proven to be very suitable for this purpose. Astigmatism Particle Tracking Velocimetry (APTV) will also be used to investigate flow profiles. On the other hand, special attention will be paid to high-resolution microscopy, such as STED and STORM, since it has become apparent that the highest possible resolution of the local distributions of crystalline and amorphous regions of cellulose, as well as the distribution of non-cellulosic polysaccharides, is of crucial importance when it comes, for example, to understanding fluid transport or which structure chemical modifications assume on the fiber surface. Last but not least, the project continues to provide important data to enable simulations of paper by capturing dynamic processes with high spatio-temporal resolution to be the basis for swelling, imbibition, and flow simulations. But also a detailed image of the static 3D structure remains fundamental for the creation of a "digital twin".In both topics - dynamics and high resolution - Deep Learning methods are applied for image enhancement, in particular for denoising, allowing extensive improvements in frame rates and resolution.

• DFG Programme: Research Grants