title: Paper-based microfluidics: fabrication technique and dynamics of capillary-driven surface flow.
abstract: Paper-based devices provide an alternative technology for simple, low-cost, portable, and disposable diagnostic tools for many applications, including clinical diagnosis, food quality control, and environmental monitoring. In this study we report a two-step fabrication process for creating two-dimensional microfluidic channels to move liquids on a hydrophobized paper surface. A highly hydrophobic surface was created on paper by TiO2 nanoparticle coating using a high-speed, roll-to-roll liquid flame spray technique. The hydrophilic pattern was then generated by UV irradiation through a photomask utilizing the photocatalytic property of TiO2. The flow dynamics of five model liquids with differing surface tensions 48-72 mN·m(-1) and viscosities 1-15 mN·m(-2) was studied. The results show that the liquid front (l) in a channel advances in time (t) according to the power law l=Zt0.5 (Z is an empirical constant which depend on the liquid properties and channel dimensions). The flow dynamics of the liquids with low viscosity show a dependence on the channel width and the droplet volume, while the flow of liquids with high viscosity is mainly controlled by the viscous forces.
authors.affiliation: Laboratory of Paper Coating and Converting and Center for Functional Materials, Abo Akademi University , Porthaninkatu 3, 20500 Åbo/Turku, Finland.
authors.forename: Joel
authors.initials: J
authors.lastname: Songok
authors.forename: Mikko
authors.initials: M
authors.lastname: Tuominen
authors.forename: Hannu
authors.initials: H
authors.lastname: Teisala
authors.forename: Janne
authors.initials: J
authors.lastname: Haapanen
authors.forename: Jyrki
authors.initials: J
authors.lastname: Mäkelä
authors.forename: Jurkka
authors.initials: J
authors.lastname: Kuusipalo
authors.forename: Martti
authors.initials: M
authors.lastname: Toivakka
mesh_terms: D002384:Catalysis; D057927:Hydrophobic and Hydrophilic Interactions; D053768:Metal Nanoparticles / Q000737:chemistry; D044085:Microfluidics; D010209:Paper; D013500:Surface Tension; D014025:Titanium / Q000737:chemistry; D014466:Ultraviolet Rays; D014783:Viscosity
chemical_list: C009495:titanium dioxide; D014025:Titanium
keywords: capillary flow; paper-based microfluidics; surface wettability control; two-dimensional lateral flow