Investigation of the Effect of the Tortuous Pore Structure on Water Diffusion through a Polymer Film Using Lattice Boltzmann Simulations

Understanding how the pore structure influences the masstransport through a porous material is important in several applications, notthe least in the design of polymer film coatings intended to control drug release.In this study, a polymer film made of ethyl cellulose and hydroxypropylcellulose was investigated. The 3D structure of the films was first experimentallycharacterized using confocal laser scanning microscopy data and thenmathematically reconstructed for the whole film thickness. Lattice Boltzmannsimulations were performed to compute the effective diffusion coefficientof water in the film and the results were compared to experimental data.The local porosities and pore sizes were also analyzed to determine how theproperties of the internal film structure affect the water effective diffusioncoefficient. The results show that the top part of the film has lower porosity,lower pore size, and lower connectivity, which results in a much lower effectivediffusion coefficient in this part, largely determining the diffusion ratethrough the entire film. Furthermore, the local effective diffusion coefficients were not proportional to the local film porosity,indicating that the results cannot be explained by a single tortuosity factor. In summary, the proposed methodology of combiningmicroscopy data, mass transport simulations, and pore space analysis can give valuable insights on how the film structure affectsthe mass transport through the film