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    Laser-Induced fluorinated graphene for superhydrophobic surfaces with anisotropic wetting and switchable adhesion

    Year: 2022

    Journal: Appl. Surf. Sci., Volume 574, FEB 1

    Authors: Nam, Ki-Ho; Abdulhafez, Moataz; Tomaraei, Golnaz Najaf; Bedewy, Mostafa

    Organizations: National Science Foundation (NSF) [2028580]; Pitt Momentum Seed grant; Department of Industrial Engineering at the University of Pittsburgh; Directorate For Engineering; Div Of Civil, Mechanical, & Manufact Inn [2028580] Funding Source: National Science Foundation

    Keywords: Laser-induced graphene; Nanocarbons; Micropatterning; Fluorinated polyimide; Heteroatom self-doping; Anisotropic wettability; Superhydrophobic surface; Parahydrophobicity; Droplet adhesion

    We present a facile direct-write approach for patterning fluorine-doped nanocarbons directly on molecularly engineered polymers for superhydrophobic and parahydrophobic surfaces. We first synthesized two different polymer films, non-fluorinated and fluorinated polyimides (PIs), by two-step procedure to create poly(amic acid) precursors, followed by thermal curing. Morphology and chemical composition were controlled by adjusting the programmed scan line pitch from 101.6 to 508 mu m during lasing to achieve superhydrophobicity with a water contact angle (CA) up to 156 degrees in the direction perpendicular to carbonized lines. Droplets exhibited strong adhesion on our porous graphene micropatterns even when held at vertical and inverted orientations, indicating a Cassie impregnating state of wetting. Parahydrophobic F-LINC with line pitch of 355.6 mu m exhibits high dynamic CAs along both perpendicular (theta(A perpendicular to) = 165 degrees, theta(R perpendicular to) = 127 degrees) and parallel directions (theta(A parallel to) = 147 degrees, theta(R parallel to) = 87 degrees) as well as highly anisotropic CA hysteresis (Delta theta(perpendicular to) = 38 degrees, Delta theta(parallel to) = 60 degrees). Moreover, we demonstrate strain-induced switchable adhesion by leveraging substrate curvature control. Further, we show that our micropatterned polymer films can be used for transferring droplets without any loss or contamination. Hence, our approach offers new insights into designing interfaces for droplet manipulation, pick-and-place applications, and localized control of reactions.
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