Abstract
Paper-based microfluidic devices are widely used in point-of-care testing applications. Imbibition study of paper porous media is important for fluid controlling, and then significant to the applications of paper-based microfluidic devices. Here we propose an analytical approach based on the infinitesimal control volume method to study the imbibition of Newtonian fluids in commonly used paper-like materials. Three common paper shapes (rectangular paper strips, fan-shaped and circular paper sheets) are investigated with three modeling methods (corresponding to equivalent tiny pores with circle, square and regular triangle cross section respectively). A model is derived for liquid imbibition in rectangular paper strips, and the control equations for liquid imbibition in fan-shaped and circular paper sheets are also derived. The model is verified by imbibition experiments done using the mixed cellulose ester filter paper and pure water. The relation of imbibition distance and time is similar to that of the Lucas−Washburn (L−W) model. In addition, a new porosity measurement method based on the imbibition in circular paper sheets is proposed and verified. Finally, the flow rates are investigated. This study can provide guidance for the design of different shapes of paper, and for better applications of paper-based microfluidic devices.
Highlights
Figure paper sheets and circular paper sheets. (b) Schematic of the infinitesimal control volume. (c) A large paper sheets and circular paper sheets. (b) Schematic of the infinitesimal control volume. (c) A large number of small circles, squares or regular triangles on the cross section of the infinitesimal control number of small circles, squares or regular triangles on the cross section of the infinitesimal control volume, which corresponds to three modeling methods. n and N1 are the number of small circle volume, corresponds to three modeling methods. n and N1 are the number of small circle layers inwhich the thickness and width direction respectively
We found that the flow rates of the three modeling methfor same paper shape havehave the same form,form, and and the results are listed in Table
We propose an analytical approach based on the infinitesimal control volume method to study the imbibition of Newtonian fluid in paper-like materials
Summary
Paper has many advantages, such as a low cost, portability, compatibility with most biochemical reactions and high flexibility [1,2,3,4,5,6,7]; it can be combined with automation technologies to form programmable paper-based microfluidic devices for better control of fluidic sample transport, mixing and reaction, to realize multiple biomarker detection, disease diagnosis, etc. [8,9,10,11,12,13,14,15]. Paper has many advantages, such as a low cost, portability, compatibility with most biochemical reactions and high flexibility [1,2,3,4,5,6,7]; it can be combined with automation technologies to form programmable paper-based microfluidic devices for better control of fluidic sample transport, mixing and reaction, to realize multiple biomarker detection, disease diagnosis, etc. Paper-based microfluidic devices have become a useful point-of-care testing (POCT) tool, there are some deficiencies, such as low sensitivity, poor reliability, and low reproducibility. One important reason is the unclear underlying mechanism of liquid flow, imbibition, in paper porous media. Imbibition study is significant for the preparation of highly sensitive, multifunctional and stable paper-based microfluidic devices. Mathematical models have been developed to understand liquid imbibition behavior
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