Simple and Reliable Method to Incorporate the Janus Property onto Arbitrary Porous Substrates

Economical
fabrication of waterproof/breathable substrates has
many potential applications such as clothing or improved medical dressing.
In this work, a facile and reproducible fabrication method was developed
to render the Janus property to arbitrary porous substrates. First,
a hydrophobic surface was obtained by depositing a fluoropolymer,
poly­(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate)
(PHFDMA), on various porous substrates such as polyester fabric, nylon
mesh, and filter paper. With a one-step vapor-phase deposition process,
termed as initiated chemical vapor deposition (iCVD), a conformal
coating of hydrophobic PHFDMA polymer film was achieved on both faces
of the porous substrate. Since the hydrophobic perfluoroalkyl functionality
is tethered on PHFDMA via hydrolyzable ester functionality, the hydrophobic
functionality on PHFDMA was readily released by hydrolysis reaction.
Here, by simply floating the PHFDMA-coated substrates on KOH­(aq) solution,
only the face of the PHFDMA-coated substrate in contact with the KOH­(aq)
solution became hydrophilic by the conversion of the fluoroalkyl ester
group in the PHFDMA to hydrophilic carboxylic acid functionality.
The hydrophilized face was able to easily absorb water, showing a
contact angle of less than 37°. However, the top side of the
PHFDMA-coated substrate was unaffected by the exposure to KOH­(aq)
solution and remained hydrophobic. Moreover, the carboxylated surface
was further functionalized with aminated polystyrene beads. The porous
Janus substrates fabricated using this method can be applied to various
kinds of clothing such as pants and shirts, something that the lamination
process for Gore-tex has not allowed.