Since the pioneering work by Whiteside <i>et al</i>. in 2007, and others, paper-based microfluidic devices have been increasingly studied owing to their great potential in various fields of application, such as point-of-care diagnostics, environmental monitoring and food quality testing. The interest in using paper as a substrate for such devices is based on the unique porous structure of paper, enabling liquid transport without any external pumping system. Through selective surface modification as e.g. hydrophobization by wax coating, a directed analyte fluid flow towards specific detector systems is possible. While the fluid flow behavior on a macroscopic scale is well investigated and can be described by various numerical models, a more detailed understanding of the fluid flow characteristics on a microscopic scale is crucial for further improvement of these paper-based analytical devices. The dominating effects governing fluid flow can be divided into wetting, swelling, diffusion, evaporation and, last but not least, capillary transport. The latter can be modulated by intrinsic paper parameters such as fiber type, fiber pretreatments or fines content as well as extrinsic parameters such as coatings. Most importantly, such dynamic water-fiber interactions are not accounted for with simple Lucas-Washburn or Darcy kinetics. Hence, it would be desirable to investigate the influence of the above mentioned effects on the dynamics of fluid flow separately from each other.<br/>In our present project, a self-developed spinning device is used to quantify the capillary forces of different paper materials by generating a force equilibrium between the capillary forces driving the fluid flow and the centrifugal forces originating from the spinning device. By analyzing the fluid flow distance until the equilibrium state between these two forces is established, conclusions about the paper intrinsic properties can be drawn. Here, a longer distance points to higher capillary pressure, which allows assumptions about the pore geometry at known fluid properties. These measurements suggest that it is in principle possible to separate capillary imbibition from fiber wetting and swelling, respectively.

Towards understanding capillary driven transport in paper: Quasi-stationary investigations using a spinning device

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.