This dissertation presents theory and methods to predict, measure, and steer the film height in soft elastohydrodynamic lubrication. It specifically focuses on the application of roll-to-plate nanoimprinting, addressing the challenges of current roller-based imprint systems to achieve uniform film heights on large-area, non-flat substrates. The research is structured in three parts, which directly correspond to the goals of film height prediction, film height measurement, and film height steering. In the first part, numerical models are developed and experimentally validated to describe the soft elastohydrodynamic lubrication in roll-to-plate nanoimprinting. The second part presents a refined analytical model and the experimental validation of the ratiometric fluorescence film height measurement method. Lastly, the third part proposes a novel concept to steer the film height in soft elastohydrodynamic lubrication, inspired by inverse lubrication theory. Overall, the developed theory and methods on film height prediction, measurement, and steering form a solid basis for future research and facilitate practical implementation to further improve the film height uniformity in soft elastohydrodynamic lubrication processes.
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This work presents the development of a numerical model for the elastohydrodynamic lubrication of roll-to-plate nanoimprinting with flexible stamps. Roll-to-plate nanoimprinting is a manufacturing method to replicate micro- and nanotextures on large-area substrates with ultraviolet-curable resins. The roller is equipped with a relatively soft elastomeric layer, which elastically deforms during the imprint process. The elastic deformation is described by linear elasticity theory. It is coupled to the pressure build-up in the liquid resin film, which is described by lubrication theory. The flexible stamp, which is treated as a tensioned web, is pre-tensioned around the roller. The elastic deformation of the tensioned web is described by the large-deflection bending of thin plates equations, considering its non-negligible bending stiffness. A Fischer–Burmeister complementarity condition captures the contact mechanics between the tensioned web and the roller. The governing equations combine in a coupled elastohydrodynamic lubrication model, which is fully described by a set of non-dimensional numbers. These are used in a parameter study to investigate the effect on the pressure and film height distributions. It is shown that the bending stiffness of the tensioned web results in an additional hydrodynamic pressure peak and corresponding minimum in the film height, near the inlet of the roller contact. An increase of the bending stiffness corresponds to a decrease in film height. The numerical results are compared with benchmarks from literature and experimentally validated with layer height measurements from flat layer imprints. Good agreement is found between the numerical and experimental results. ... Read more

Roll-to-plate nanoimprinting with flexible stamps is a fabrication method to pattern large-area substrates with micro- and nanotextures. The imprint consists of the preferred texture on top of a residual layer, of which the thickness and uniformity is critical for many applications. In this work, a numerical model is developed to predict the residual layer thickness (RLT) as a function of the imprint parameters. The model is based on elastohydrodynamic lubrication (EHL) theory, which combines lubrication theory for the pressure build-up in the resin film, with linear elasticity theory for the elastic deformation of the roller material. The model is extended with inextensible cylindrical shell theory to capture the effect of the flexible stamp, which is treated as a tensioned web. The results show that an increase in the tension of the web increases the effective stiffness of the roller, resulting in a reduction in the RLT. The numerical results are validated with layer height measurements from flat layer imprints. It is shown that the simulated minimum layer height corresponds very well with the experimental results for a wide range of resin viscosities, imprint velocities, and imprint loads ... Read more