key: cord-347390-xz5a99cr authors: Ray, Saikat Sinha; Park, You-In; Park, Hosik; Nam, Seung-Eun; Kim, In-Chul; Kwon, Young-Nam title: Surface innovation to enhance anti-droplet and hydrophobic behavior of breathable compressed-polyurethane masks date: 2020-08-07 journal: Environ Technol Innov DOI: 10.1016/j.eti.2020.101093 sha: doc_id: 347390 cord_uid: xz5a99cr With the emergence of the coronavirus disease (COVID-19), it is essential that face masks demonstrating significant anti-droplet and hydrophobic characteristics are developed and distributed. In this study, a commercial compressed-polyurethane (C-PU) mask was modified by applying a hydrophobic and anti-droplet coating using a silica sol, which was formed by the hydrolysis of tetraethoxysilane (TEOS) under alkaline conditions and hydrolyzed hexadecyltrimethoxysilane (HDTMS) to achieve hydrophobization. The modified mask (C-PU/Si/HDTMS) demonstrated good water repellency resulting in high water contact angle (132°) and low sliding angle (17°). Unmodified and modified masks were characterized using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). A drainage test confirmed the strong interaction between the mask surface and coating. Moreover, the coating had negligible effect on the average pore size of the C-PU mask, which retained its high breathability after modification. The application of this coating is a facile approach to impart anti-droplet, hydrophobic, and self-cleaning characteristics to C-PU masks. This mask is based on porous filter technology which controls the pores to form the ideal 74 density and size for trapping pollen sized particles. In addition to that, it can be reused even 75 after 2-3 washes. Above all, it is highly cheap and commercially available that delivers 76 overwhelming air permeability. Nonetheless, due to high water absorbency as a result of the 77 hydrophilicity of the masks diminishes their water-repelling properties but may be solved by a 78 coating that imparts hydrophobic as well as anti-droplet features. In this study, a simple 79 fabrication approach was demonstrated wherein tetraethyl orthosilicate (TEOS) is hydrolyzed 80 in a H2O/ethanol solution mixture to form silane sol and hexadecyltrimethoxysilane (HDTMS) 81 is hydrolyzed in ethanol solution to form an alkylsilanol. Until now, fluorinated based material 82 or coating has been used as one of the effective agents for lowering the surface free energy. 83 But recent research suggests that, fluorinated materials are expensive as well as not 84 environmentally friendly [11] . In this study, a non-fluoro compound, 85 hexadecyltrimethoxysilane (HDTMS), an organosilane with a C-16 hydrocarbon tail, has been 86 utilized to modify the surface of silica. Typically, HDTMS is an amphiphilic molecule 87 consisting of hydrophilic head where a central silicon atom is attached to three -OCH3 groups, 88 and its hydrophobic tail is composed of an alkyl chain formed by a straight succession of fifteen 89 CH2 groups and one CH3 group at its end. The results in long-chain alkylsilane with low surface 90 free energy has been introduced onto SiO2 grafted surfaces, hence, generating the modified 91 hydrophobic surface [12] . The C-PU mask sample was first treated with the silica sol and then the same sample was As far as the structural aspect is concerned, the inner spongy layer is kept unchanged and was 117 found to be hydrophilic in nature that helps in absorbing moisture. In addition to that, the 118 compressed polyurethane masks are non-allergic in nature that are comfortable with face/skin. However, the outer layer has been chemically modified that was observed to be hydrophobic 120 for droplet/ splash resistance application. Moreover, the porous structure demonstrates the 121 capability of high air permeability. Thus, this dual layer concept has been applied in the present 122 study to reduce the chance of contamination from water droplets or splashes. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 was constantly stirred for one and half hour to produce the silica sol. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 The methodology for fabricating a stable hydrophobic coating on a mask surface utilizing silica 202 sol as well as HDTMS is discussed in materials and methods section and summarized in 203 Scheme 1. Silica sol specimens (Si-1 and Si-2) with different particle sizes were synthesized 204 by adjusting the content of NH4OH while generation of the silica sol as indicated in Table 1 . The polydispersity index (PDI) value can be used to evaluate the average uniformity of a 206 particle or nanoparticle dispersion [20, 21] . Interestingly, values greater than 0.8 indicate low 207 stability for a drug delivery/nano-delivery/colloidal system. 208 Si-2 6 ml 100 ml 6 ml 0.5 The particle size distribution of the silica samples (Si-1 and Si-2) is shown in Figure 3 . It is 211 evident that the average particle size of the silica sol escalates as the content of NH4OH is 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 water contact angle, even after 15 min. It is worth noting that the C-PU/Si-2/HDTMS mask 252 records a higher water contact angle than the C-PU/Si-1/HDTMS mask, which is ascribed to 253 the increased aggregation and average particle size of the Si-2 sol (Figure 3) . The C-PU/Si- 254 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J o u r n a l P r e -p r o o f Journal Pre-proof to base produced from the liquid and the surface. As per Table 2 , droplet volume was kept 263 consistent and droplet height has been investigated to examine the degree of wetting state of 264 pristine and modified mask. Interestingly, higher droplet height indicates higher contact angle 265 while keeping the droplet water volume (10 µL) same. This outcome has been found to be 266 consistent as indicated in Figure 6 . 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 The morphology of unmodified and modified masks was investigated using SEM, refer to concluded that the air permeability or breathability of these masks aren't significantly changed. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 indicates higher air permeability that leads to high breathability. In order to examine the 302 internal structure, the cross-sectional morphology has been thoroughly studied that indicates 303 same internal structure for both masks. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 The thickness of the masks was evaluated using a digital thickness gauge at ten different 327 locations and averaged for further calculations. Typically, face masks are made in various 328 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 "mechanical" collection mechanism that involves inertial impaction, interception and 335 diffusion. This mechanism helps in trapping particles without increasing breathing resistance 336 [32]. Hence, thicker the filter, the better the protection from foreign particles. However, it 337 shouldn't be too thick as it may resist air permeability if the filter is too dense. But, in this 338 study, polyurethane material was found to be extremely porous. material. This crucial factor is influenced by the porosity of the material, that in turn impacts 343 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 J o u r n a l P r e -p r o o f Therefore, air permeability can also be correlated based on porosity value. Material permeability is often evaluated with respect to the porosity of the fabric. The porosity 346 of the material (ε) has been evaluated as follows [34] : where Wwet and Wdry represent the weights of the wet and dried material (g); ρwater represents 349 water density in g/cm 3 ; whereas; A and h indicate the area (cm 2 ) and thickness (cm), 350 respectively, of the material. Figure 12 shows the measured porosity of various mask materials. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 The durability of the surface coating was qualitatively investigated by conducting a water jet 403 impact test. In this study, the water jet was quickly repelled by the modified mask and the 404 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 Features, evaluation and treatment 440 coronavirus (COVID-19), Statpearls Coronavirus disease 2019 (COVID-19): situation report The epidemiology and pathogenesis of coronavirus disease (COVID-448 19) outbreak Face mask use and control of respiratory virus transmission in households, Emerging 451 infectious diseases To 453 mask or not to mask: Modeling the potential for face mask use by the general public to curtail the 454 COVID-19 pandemic A Flexible Nanoporous Template 456 for the Design and Development of Reusable Anti-COVID-19 Hydrophobic Face Masks How to Safely Wear and Take Off a Cloth Face Covering An 460 Efficient Ethanol-Vacuum Method for the Decontamination and Preparation of hexadecyltrimethoxysilane-modified silica 463 nanocomposite hydrosol and superhydrophobic cotton coating Superhydrophobic cotton fabrics prepared by one-step water-466 based sol-gel coating Silica nanocomposite based hydrophobic functionality 468 on jute textiles Inorganic micro-and nanostructured implants for 470 tissue engineering Emerging Developments in the Use of Electrospun Fibers and 472 Membranes for Protective Clothing Applications The environmental dangers of employing single-use face 475 masks as part of a COVID-19 exit strategy Mask-induced contact dermatitis in handling COVID-19 outbreak A thermodynamic model of contact angle hysteresis Polymer-based multifunctional nanocomposites and their applications Physical characterization of 483 nanoparticle size and surface modification using particle scattering diffusometry Eco-friendly curcumin-loaded 486 nanostructured lipid carrier as an efficient antibacterial for hospital wastewater treatment Size, volume fraction, and 489 nucleation of Stober silica nanoparticles Porous biodegradable polyurethane 491 nanocomposites: preparation, characterization, and biocompatibility tests Comparison between SiOC thin film by plasma enhance chemical vapor deposition and 494 SiO 2 thin film by Fourier transform infrared spectroscopy Review on blueprint of designing anti-wetting polymeric 497 membrane surfaces for enhanced membrane distillation performance Synthesis and characterization of nanocomposite ultrafiltration membrane (PSF/PVP/SiO2) and performance 500 evaluation for the removal of amoxicillin from aqueous solutions Durable, self-healing, 503 superhydrophobic fabrics from fluorine-free, waterborne, polydopamine/alkyl silane coatings Hydrophobic/hydrophilic patterned surfaces for 506 directed evaporative preconcentration Design of super-hydrophobic microporous 508 polytetrafluoroethylene membranes Morphological and structural 510 developments in nanoparticles polyurethane foam nanocomposite's synthesis and their effects on 511 mechanical properties Performance of fabrics for home-made masks against spread 513 of respiratory infection through droplets: a quantitative mechanistic study, medRxiv A short review on the development of novel face masks during 515 COVID-19 pandemic Nanotechnology in Textiles: Theory and Application Air permeability & porosity in spun-laced fabrics, Fibres and Textiles in Eastern 519 Contact angles and wettability: 521 towards common and accurate terminology Typically, facets of real surfaces such as surface roughness and chemical heterogeneity, may