Face masks will be used to prevent pandemic recurrence and outbreaks of mutant SARS-CoV-2 strains until mass immunity is confirmed. The polypropylene (PP) filter is a representative disposable mask material that traps virus-containing bioaerosols, preventing secondary transmission. In this study, a copper thin film (20 nm) was deposited via vacuum coating on a spunbond PP filter surrounding a KF94 face mask to provide additional protection and lower the risk of secondary transmission. Film adhesion was improved using oxygen ion beam pretreatment, resulting in cuprous oxide formation on the PP fiber without structural deformation. The copper-coated mask exhibited filtration efficiencies of 95.1 ± 1.32% and 91.6 ± 0.83% for NaCl and paraffin oil particles, respectively. SARS-CoV-2 inactivation was evaluated by transferring virus-containing media onto the copper-coated PP filters and subsequently adding Vero cells. Infection was verified using real-time polymerase chain reaction and immunochemical staining. Vero cells added after contact with the copper-coated mask did not express the RNA-dependent RNA polymerase and envelope genes of SARS-CoV-2. The SARS-CoV-2 nucleocapsid immunofluorescence results indicated a reduction in the amount of virus of more than 75%. Therefore, copper-coated antiviral PP filters could be key materials in personal protective equipment, as well as in air-conditioning systems.

The spatial distribution of binding states in the depth direction of a soft polydimethylsiloxane (PDMS) material was investigated in the hard skin layer formed by Ar ion-beam irradiation. The hard skin layer, typically considered silica-like and homogeneous, was heterogeneous, comprising a topmost layer and an intermediate layer. Impinging Ar ions transferred energy to the PDMS medium by collisional energy transfer, which was maximised at the surface and decreased gradually as the ions penetrated the PDMS. The decreasing energy transfer rate from the surface created a heterogeneous hard skin layer. X-ray photoelectron spectroscopic depth profiling showed the existence of the topmost and intermediate layers. In the topmost layer, scission and cross-linking occurred simultaneously; Si–O bonds showed the dissociated state of SiOx (x = 1.25–1.5). Under the topmost layer, the intermediate layer showed mostly cross-linking, with Si–O bonds showing silica-like binding states of SiOx (x = 1.75–2). The spatial distribution of carbon-related bonds such as C–Si and sp3 C–C also showed heterogeneity, yielding a gradient of bond distribution. A theoretical analysis of the collisional energy transfer rate and displacement per atom showed consistency with the XPS depth profiling results.

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This work reports the self-organization of dimple nanostructures on a polyethylene naphthalate (PEN) surface where an Ar ion beam was irradiated at an ion energy of 600 eV. The peak-to-peak roughness and diameter of dimple nanostructures were 29.1~53.4 nm and 63.4~77.6 nm, respectively. The electron energy loss spectrum at the peaks and troughs of dimples showed similar C=C, C=O, and O=CH bonding statuses. In addition, wide-angle X-ray scattering showed that Ar ion beam irradiation did not induce crystallization of the PEN surface. That meant that the self-organization on the PEN surface could be due to the ion-induced surface instability of the amorphous layer and not due to the partial crystallinity differences of the peaks and valleys. A nonlinear continuum model described surface instability due to Ar ion-induced sputtering. The Kuramoto–Sivashinsky model reproduced the dimple morphologies numerically, which was similar to the experimentally observed dimple patterns. This preliminary validation showed the possibility that the continuum equation used for metal and semiconductor surfaces could be applied to polymer surfaces where ion beam sputtering occurred.