NMR imaging of liquid distributions inside coated paper during synchronized imbibition and swelling

Liquid imbibition into coated paper is different from paper without a coating due to the flow resistance induced by the low permeability of the coating layer. It was concluded that liquid uptake and paper swelling are synchronized, and occurs locally at the tip of the liquid front. This is significantly different from liquid imbibition in uncoated paper, where liquid penetrates quickly and later swelling occurs more homogeneously throughout the paper. Moreover, it has been shown that both the imbibition and swelling speed are determined by viscosity. Consequently, Darcy's law for unsaturated flow still holds in this complex layered medium. This knowledge gets us a step closer to controlling liquid-media interactions in many different applications.