Abstract
The fabrication and properties of “fluoroalkylated paper” (“RF paper”) by vapor‐phase silanization of paper with fluoroalkyl trichlorosilanes is reported. RF paper is both hydrophobic and oleophobic: it repels water (θappH2O>140°), organic liquids with surface tensions as low as 28 mN m‐1, aqueous solutions containing ionic and non‐ionic surfactants, and complex liquids such as blood (which contains salts, surfactants, and biological material such as cells, proteins, and lipids). The propensity of the paper to resist wetting by liquids with a wide range of surface tensions correlates with the length and degree of fluorination of the organosilane (with a few exceptions in the case of methyl trichlorosilane‐treated paper), and with the roughness of the paper. RF paper maintains the high permeability to gases and mechanical flexibility of the untreated paper, and can be folded into functional shapes (e.g., microtiter plates and liquid‐filled gas sensors). When impregnated with a perfluorinated oil, RF paper forms a “slippery” surface (paper slippery liquid‐infused porous surface, or “paper SLIPS“) capable of repelling liquids with surface tensions as low as 15 mN m‐1. The foldability of the paper SLIPS allows the fabrication of channels and flow switches to guide the transport of liquid droplets.
Highlights
The design of devices that handle liquids, or control the transport of gases, would benefit from new materials, and from repurposing currently available materials to have new properties and functions
Water-repellent materials based on expanded polytetrafluoroethylene and other polymers have been useful in a wide range of applications, from high performance fabrics and membrane filters to fuel cells,[1] surgical implants[2,3,4,5] and lung-assist devices.[6, 7]
We show that a rapid, one-step reaction with a fluoroalkyl trichlorosilane in the gas phase transforms cellulose paper into RF paper, an omniphobic material that is not wetted by water and organic liquids with surface tension as low as 28 mN/m
Summary
The design of devices that handle liquids, or control the transport of gases, would benefit from new materials, and from repurposing currently available materials to have new properties and functions. Paper is a useful substrate in applications that require low cost, flexibility, disposability, porosity, and adaptability to large-scale manufacturing.[8,9,10,11] In recent years, it has become increasingly popular as a material for the construction of “high-tech” devices in consumer electronics, [12,13,14] chemical and physical microelectromechanical systems (MEMS) sensors,[8, 15,16,17] user interfaces,[18] electronic displays,[19] cell-based assays[20] and microfluidic devices.[10, 21] The tendency of paper to absorb solvents (including water), limits its adoption as a substrate in liquid-handling applications in which wicking is not desirable, or in which moisture and humidity can cause deleterious effects (especially changes in mechanical and electrical properties). We characterized the wetting behavior of the RF paper, and used it to fabricate functional paper-based devices: microtiter plates able to contain polar and non-polar solvents, and gas sensors, both constructed using the principles of origami.[42]
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