Abstract
Two commodity polymers, polystyrene (PS) and high-density polyethylene (HDPE), were irradiated by high-energy He ion beams at low fluence to examine the wettability changes at different fluences. The water contact angles of the PS and HDPE surfaces were reduced from 78.3° to 46.7° and 81.5° to 58.5°, respectively, upon increasing the fluence from 0 to 1 × 1013 He2+/cm2 for irradiation durations ≤4 min. Surface analyses were performed to investigate these wettability changes. Surface texture evaluations via scanning electron and atomic force microscopies indicated non-remarkable changes by irradiation. However, the chemical structures of the irradiated polymer surfaces were notable. The high-energy He ions induced nuclear transmutation of C to N, leading to C–N bond formation in the polymer chains. Further, C–O and C=O bonds were formed during irradiation in air because of polymer oxidation. Finally, amide and ester groups were generated by irradiation. These polar groups improved hydrophilicity by increasing surface energies. Experiments with other polymers can further elucidate the correlation between polymer structure and surface wettability changes due to high-energy low-fluence He ion irradiation. This method can realize simple and effective utilization of commercial cyclotrons to tailor polymer surfaces without compromising surface texture and mechanical integrity.
Highlights
Engineering the surface wettability of solids has been intensively studied to improve the adhesion of coating/printing/painting, lower friction between different surfaces, and achieve functional surfaces that exhibit self-cleaning/anti-icing/anti-fingerprint properties
The as-prepared polymer samples were irradiated by a He ion ( called alpha (α) particle) beam with energy 20 MeV and current 50 nA using the MC-50 Cyclotron installed at the Korea Institute of Radiological and Medical Sciences (KIRAMS)
The average contact angle (CA) of pristine PS and high-density polyethylene (HDPE) was 78.3◦ and 81.5◦, respectively, which significantly decreased to 46.7◦ and 58.5◦ at 1 × 1013 He2+ /cm2
Summary
Engineering the surface wettability of solids has been intensively studied to improve the adhesion of coating/printing/painting, lower friction between different surfaces, and achieve functional surfaces that exhibit self-cleaning/anti-icing/anti-fingerprint properties. Self-assembled monolayers (e.g., sol-gel method and phase separation) are typical chemical routes used to functionalize or oxidize solid surfaces by introducing hydrophilic groups (surface chemistry) [1,2,3,4]. These routes can affect the surface texture by etching the surface. These chemical routes are effective for engineering surface wettability; they usually require precise and controlled conditions for time-consuming reactions. Low-energy particle (mostly ions) bombardment is usually accompanied by these methods, which effectively alters the surface properties; there is a compromise in the mechanical strength because of the etching of the solid
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