Abstract
Poly-p-xylylene films have been utilized as protective and barrier layers for gases and solvents on electronic and implantable devices. Here we report a new approach to create highly permeable and selective nanofiltration membranes coated with microporous poly-p-xylylene nanofilms fabricated through a dry chemical vapor deposition process by using [2.2]paracyclophanes derivatives on ultrafiltration membranes. The introduction of crosslinking points into rigid poly-p-xylylenes enhanced microporosity and mechanical strength due to insufficient packing and depression of structural relaxation among polymer chains in three-dimensional networks. Crosslinked nanofilms with thicknesses down to 50 nm showed outstanding permeability for water and alcohols at a pressure difference of 0.5 MPa and exhibited higher rejection ratios for water-soluble organic dyes than non-crosslinked nanofilms. Poly-p-xylylene nanofilms also showed an excellent blocking property for non-polar organic solvent permeation through specific interaction of hydrophilic pores with organic solvents.
Highlights
All-carbon-structural and high-molecular-weight poly-p-xylylenes (Parylene), in which benzene rings are connected by ethylene linkers, have been widely used as protective coatings of printed circuits and medical devices, barrier layers of metal surfaces to prevent corrosion, and lubricants[17]
Process, two p-xylylene monomers are formed by vacuum vapor pyrolysis of [2.2]paracyclophane above 550 °C, and the reactive monomers polymerize into pure poly-p-xylylenes on the surface of targets at room temperature in a vacuum ambient
The membranes coated with crosslinked nanofilms 6 and 7 showed higher water permeance values than non-crosslinked 3 and 4, indicating the enhancement of microporosity created by the inefficient packing of polymer chains within the crosslinked nanofilms
Summary
Takeshi Shii[1], Masaru Hatori[1], Kazuma Yokota[1], Yoshiyuki Hattori1 & Mutsumi Kimura[1,2]. Conformal coating of various devices with poly-p-xylylene films exhibits outstanding barrier properties for gasses, water, and organic solvents owing to dense packing of rigid polymer chains. The molecular weight cut-off (MWCO) for 3 and 4 were 1500 g/mol, determined from the rejection measurements of polyethylene glycols with different molecular weights (Fig. S10) From these results, poly-p-xylylene nanofilms 3 and 4 work as selective layers that have a molecular size cutoff in accordance with their free volume size. The membranes coated with crosslinked nanofilms 6 and 7 showed higher water permeance values than non-crosslinked 3 and 4, indicating the enhancement of microporosity created by the inefficient packing of polymer chains within the crosslinked nanofilms. The nanofilm 7 can separate water from the mixtures of alkanes and water in the presence of surfactants (Fig. 4)
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