Fluorine-Free Transparent Superhydrophobic Nanocomposite Coatings from Mesoporous Silica

Abstract

In recent decades, there has been a growing interest in the development of functional, fluorine-free superhydrophobic surfaces with improved adhesion for better applicability into real-world problems. Here we compare two different methods, spin coating and aerosol assisted chemical vapor deposition (AACVD), for the synthesis of transparent fluorine-free superhydrophobic coatings. The material was made from a nanocomposite of (3-aminopropyl)triethoxysilane (APTES) functional mesoporous silica nanoparticles and titanium crosslinked polydimethylsiloxane with particle concentrations between 9 wt% to 50 wt%. The silane that was used to lower the surface energy consisted of a long hydrocarbon chain without fluorine groups to reduce the environmental impact of the composite coating. Both spin coating and AACVD resulted in the formation of superhydrophobic surfaces with advancing contact angles up to 168°, a hysteresis of 3° and a transparency of 90% at 550 nm. AACVD has proven to produce more uniform coatings with concentrations as low as 9 wt% reaching superhydrophobicity. The metal oxide crosslinking improves the adhesion of the coating to the glass. Overall, AACVD was the more optimal method to prepare superhydrophobic coatings compared to spin coating due to higher contact angles, adhesion and scalability of the fabrication process.

Production of an EP/PDMS/SA/AlZnO Coated Superhydrophobic Surface through an Aerosol-Assisted Chemical Vapor Deposition Process

“… 36 The technique has been widely used to study superhydrophobic surfaces. 27 , 37 − 39 The aerosolized precursor is delivered and deposited to a substrate in the AACVD chamber during the process. 36 Depending on the type of precursor, single or multiple deposition processes have been used to produce superhydrophobic surfaces.…”

“… 36 Depending on the type of precursor, single or multiple deposition processes have been used to produce superhydrophobic surfaces. 27 , 37 − 39 For example, Tombesi et al . introduced a layer-by-layer deposition using 3-methacryloxypropyltrimethoxysilane and tetraethyl orthosilicate (TEOS) while Zhuang et al described a single-step deposition using PDMS and TEOS.…”

Hydrophobic Mesoporous Silica Particles Modified With Nonfluorinated Alkyl Silanes

“…22−25 Stable fluorinated groups decrease the van der Waals potential with the result that electrostatic interactions limit contact between the solid and liquid phases, resulting in wider contact angles. 26 However, several recent reports have shown that the risk of the use of fluorine-based compounds involves risks of environmental contamination and human health issues such as incurable diseases (e.g., thyroid disease, cancer, and Alzheimer's syndrome), immune disorders, and hormonal disorders. 27−32 In addition, a rough-textured surface and low surface energy are required to form a hydrophobic surface.…”

“…The hydrophobic surface modification method that has been widely used so far is the use of fluorine compounds such as poly­(tetrafluoroethylene) (PTFE, Teflon) and perfluoroalkyl groups. − Because fluorine has a small atomic diameter (42 pm) and a large electronegativity (3.98), it is advantageous for lowering the surface free energy. − Stable fluorinated groups decrease the van der Waals potential with the result that electrostatic interactions limit contact between the solid and liquid phases, resulting in wider contact angles . However, several recent reports have shown that the risk of the use of fluorine-based compounds involves risks of environmental contamination and human health issues such as incurable diseases (e.g., thyroid disease, cancer, and Alzheimer’s syndrome), immune disorders, and hormonal disorders. − In addition, a rough-textured surface and low surface energy are required to form a hydrophobic surface.…”

Non-Fluorinated, Superhydrophobic Binder-Filler Coatings on Smooth Surfaces: Controlled Phase Separation of Particles to Enhance Mechanical Durability

“…For these reasons, recent research efforts have begun to emphasize superhydrophobic materials fabricated from non-fluorinated components. Alternatives to perfluorinated materials include hydrophobic alkyl chains, poly­(dimethyl siloxane), − and even inherently hydrophilic materials such as silicon when incorporated into doubly re-entrant surface structures . Despite the contributions from those reported works, it remains a major challenge to simultaneously achieve superhydrophobicity and high inherent mechanical durability, especially using non-fluorinated materials.…”