Engineering microfluidic papers: determination of fibre source and paper sheet properties and their influence on capillary-driven fluid flow

In the present study, the surface chemistry of fibres from different sources (groundwood, cotton linters, eucalyptus sulphate and a mixture of pine sulphate and spruce sulphate) was initially assessed via inverse gas chromatography. Significant differences were revealed among the four fibre types, especially between groundwood and the other three with regard to the surface energy and to the specific component of the work of adhesion of different polar probes. Moreover, the freeness value and the specific surface area of the diverse fractionated and unfractionated fibrous materials were investigated. In addition, the porosity and the pore size distribution of lab engineered paper sheets produced with the previously mentioned fibre sources were studied while modifying the fibre length and grammage. Novel approaches to modulate and control fluid transport in the lab-engineered paper substrates were introduced by using different fibre sources with the same freeness value, by fractionating the fibres before fabricating the paper substrates, and by changing the orientation of the fibres. The experimental results for our lab-engineered paper substrates and commercially available filter paper were compared with each other. Our findings suggest a considerable improvement in liquid transport velocity of tailor-made microfluidic paper based analytical devices with lab-engineered paper substrates. By altering the mentioned fibre and paper values, we managed to reduce or raise the capillary rise, which eventually allows us to modulate and control fluid flow in a more accurate and desirable way. Finally, changes in the fluid transport for paper substrates laid on materials with different water contact angles were tested. The obtained information thereby provides an alternative method to increase or decrease the capillary rise.