Superhydrophobic 3D Porous PTFE/TiO₂ Hybrid Structures

Abstract

or partially removed, superhydrophobicity properties vanish easily. Such 2D surfaces provide a metastable superhydrophobic state since the limited entrapped air in such surfaces disappears quickly in contacting with water and the surface gets completely wetted within a short time. In contrast, 3D structures maintain trapped air at the surface and through whole bulk. [7] These kinds of structures may provide a stable and long-running superhydrophobicity since penetrating water will meet continuously with a fresh trapped-air barrier. It is essential to extend the surface topographies responsible for superhydrophobicity into the bulk by creating both roughness and low surface energy to achieve superhydrophobic 3D materials.Herein, a commercially available polyurethane (PU) foam was utilized as the sacrificial hard template to infiltrate TiO 2 nanoparticles in its interstitial pores. By simply burning out PU template and sintering at 850-900 °C, a 3D TiO 2 skeleton (forming inner and outer macropores) was achieved by 2D assembling of TiO 2 nanoparticles through the whole bulk. By combining macrolevel pores and the micro-/nanostructured topography, a 3D high surface roughness was achieved (Figure 1a; Figure S1, Supporting Information). The prepared TiO 2 slurry was also applied to planar quartz substrates by double-doctor blade coating technique to achieve micro-/nanostructured 2D TiO 2 (Figure 1a; Figure S2, Supporting Information). Afterward, initiated chemical vapor deposition (iCVD) was carried out to coat 2D and 3D TiO 2 homogenously with a thin layer of polytetrafluoroethylene (PTFE) while conserving the inner micro-and nanotopography (as shown schematically in Figure 1b). iCVD allows coating various types of substrates varying from simple 2D to complex 3D structures with a high conformity (without altering topographic details of the pristine structure). [8] After coating a thin layer of PTFE, 3D TiO 2 showed an extraordinary superhydrophobicity.3D TiO 2 has a porous structure with the pore size of ≈100-150 µm (Figure 2a) and exhibits approximately the same micro-and nanoscale structures with 2D TiO 2 surface prepared for the comparison by the well-established doctor blade technique. [9] While 2D surface was composed of micro/nano hierarchical porous texture, 3D surface consists additionally macropores (Figure 2a). Clearly micro-and nanoscale roughness was provided through the whole bulk in 3D TiO 2 . Following the iCVD step, we did not observe any significant change in the morphology of both 2D and 3D TiO 2 . This indicates that the deposited PTFE layer was extremely thin and highly conformal. Figure 2b shows the X-ray photoelectron spectroscopy (XPS) survey spectra of the uncoated and coated 3D TiO 2 . Simply Combining hard-templating and infiltration processes, micro-and nanoscale topography induced by 2D assembling of TiO 2 nanoparticles is extended to 3D TiO 2 . By applying an ultrathin and highly conformal polytetrafluoroethylene (PTFE) layer on prepared 3D TiO 2 via initiated chemical vapor deposition (iC...

Nanoscale control by chemically vapour-deposited polymers

“…129,130 By optimizing processing conditions, iCVD can infill porous and textured substrates. The infiltration of iCVD fluoropolymers into TiO2 nanoparticles matrices produces composite films with high loadings of inorganic particles 131 and bulk hybrid composites acting as superhydrophobic sponges 132 . Modified iCVD processes can achieve global and local planarization of surfaces features on silicon wafers.…”

Selective Adsorption and Photocatalytic Clean‐Up of Oil by TiO2 Thin Film Decorated with p‐V3D3 Modified Flowerlike Ag Nanoplates

“…Indeed, this is in agreement with Wenzel's rule which states that an intrinsically hydrophilic material will become more hydrophilic by increasing the surface roughness and/or introducing hierarchical roughness. [24][25][26][27] To further confirm the surface roughness, which plays an important role in enhancing the wettability properties of flowerlike Ag nanoplates on TiO 2 , the surface topography of the prepared samples was analyzed by atomic force microscopy (AFM) as shown in Figure S3 of the Supporting Information. The average surface roughness (Ra) and root mean square roughness (rms) were measured as 704.4 (± 24.6) nm and 744.8 (± 26.1) nm for Ag/ TiO 2 and 18.9 (± 1.1) nm and 23.8 (± 1.3) nm for bare TiO 2 , respectively; which clearly indicates a significant change in surface roughness after photocatalytic deposition of flower like Ag nanoplates.…”

“…Deposition of Polymer Layer by iCVD: p-V 3 D 3 layer was deposited on prepared Ag/TiO 2 samples in a custom-built iCVD reactor system operated in a constant flow mode, as described before. [27,46,47] First the reactor was evacuated for at least 3 h before introducing the monomer (1,3,5-trivinyl-1,3,5-trimethylcyclotrisiloxane, V 3 D 3 -ABCR, Germany) and the initiator perfluorobutanesulfonyl fluoride (PFBSF, 95% Fluorochem, UK). The reactor pressure was set to 50 Pa and controlled by a downstream butterfly valve (VAT Series 615), coupled to a capacitance manometer (MKS Baratron), that is connected to the reactor.…”

Robust surface with thermally stable hydrophobicity enabled by electrosprayed fluorinated SiO2 particles

“…2,13,14 To simultaneously achieve high thermal stability and hydrophobicity, micro/nanostructured surfaces are fabricated with inorganic materials and modified by chemicals with low surface energy. 7,15,16 However, this strategy cannot impart high thermal stability and mechanical robustness simultaneously. Meanwhile, the organic fluorinate molecules grafted on the surfaces are usually vulnerable to long-term high-temperature use, thus limiting their practical use.…”