Fluid flow modulation in porous materials and especially in paper is highly relevant for many applications from delivery, lab-on-chip devices to sensors and membranes. Microfluidic paper-based devices, as introduced by Whitesides in 2007, are low-cost, disposable and thus sustainable. But the role of the fiber nanoporosity on transport is often neglected and it is hard to control and maintain during the preparation process.<br/>The presented study provides deeper insights into the role of the fiber surface and nanoporosity on the capillary fluid flow by comparing water uptake of dense or mesoporous silica coated cotton linters paper. This fluid stop is observed macroscopically as well as microscopically following fluid flow into the paper fiber structure by resolution fluorescence microscopy. Specifically, we are able to stop fluid flow by adjusting fiber density and the mesporosity of the silica fiber coating while using all hydrophilic materials. Secondly, our study introduces a method to functionalize silica-coated paper of different fiber mesoporosity in a way that capillary fluid flow can be gated on and off by external redox stimuli. To this end we functionalize hybrid silica-paper sheets with redox-responsive polymers allowing reversible, dynamic gating of fluid flow, demonstrating the potential of length scale specific, dynamic, and external transport control. This behavior has been extended to other fibers like eucalyptus allowing to derive systematic understanding into the cross correlation of fiber mesoporosity and wetting on fluid transport in paper.

Fluid flow in paper-derived silica-polymer hybrids

255th National Meeting (2018)

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