Preparation and properties of polydimethylsiloxane/MCM-41 superhydrophobic coatings

Preparation and properties of polydimethylsiloxane/MCM-41 superhydrophobic coatings
Superhydrophobic coatings have received much attention from researchers because they exhibit excellent characteristics such as anti-icing, oil-water separation resistance, anti-fogging, self-cleaning, anti-fouling, and drag reduction. There are two main schemes to prepare superhydrophobic coatings: (1) roughening the hydrophobic surface; (2) introducing low surface energy materials to hydrophobically modify the rough surface.

The methods for roughening the hydrophobic surface using option (1) include: electrostatic spinning, chemical vapor deposition (CVD), plasma etching, sol-gel, photolithography, and so on. However, the above methods have drawbacks such as expensive equipment costs, complex processes, and high requirements for operating techniques.
In order to overcome the above problems, researchers usually adopt scheme (2), i.e., introducing low surface energy materials to hydrophobically modify the rough surfaces, usually using chemical modification such as grafting to introduce organosilicon or organofluorine functional groups, so that they can be combined with silicon dioxide nanoparticles (SiO2 NPs) through chemical bonding to obtain hydrophobically functionalized SiO2 NPs, and then through the resin matrix, chemisorption The functionalized SiO2 NPs were then firmly bonded to the substrate by resin matrix, chemical adsorption, or physical adsorption to form a superhydrophobic coating.Tian et al. modified the SiO2 NPs by introducing 1H,1H,2H,2H-perfluorododecyltriethoxysilane (PFDTES), which chemically bonded the SiO2 NPs through functional group grafting, but this method introduced fluorinated functional groups, which may cause pollution to the environment, and employed a Sun et al. used a two-step approach to hydrophobic modification of SiO2 NPs, firstly, SiO2 NPs were modified with vinyltriethoxysilane (VTEOS), and then the silane-modified SiO2 NPs were reacted with styrene (St), so that some hydrophobic functional groups on St were grafted onto SiO2 NPs particles to realize hydrophobic modification. to realize the hydrophobic modification. Seyfi et al. used a simple spraying method to prepare a superhydrophobic coating of elastic polyurethane (TPU)/modified SiO2 NPs, but introduced a more complicated grafting method, which resulted in poor mechanical properties and high temperature curing, which wasted energy. Wang et al. designed a method to improve the abrasion resistance of superhydrophobic coatings by introducing siloxane monomers to coat SiO2 NPs, forming a complex reticulated particle structure to achieve hydrophobic modification of SiO2 NPs, and then mixing them with poly(methylhydrosiloxane) (PMHS) to prepare

superhydrophobic coatings, which were able to withstand 150 cycles of abrasion and 500 times of tape stripping tests. However, this method still employs the grafting method to modify SiO2 NPs and requires high temperature curing. From the above study, it can be seen that the modification method of common SiO2 (nonporous SiO2) is limited to chemical grafting method.

Based on the limitations of nonporous SiO2 modification, mesoporous SiO2 nanoparticles (MCM-41) were introduced in this study.MCM-41, characterized by a large specific surface area (900 m2/g) and an internal porous structure (pore size of 2-20 nm), has been used in catalyst carriers, life medicine, and drug-carrying applications, but it has rarely been applied in superhydrophobicity.
In this study, we propose a simple and easy method to prepare superhydrophobic coatings that can be applied on a large scale: firstly, by utilizing the characteristics of MCM-41’s internal porous structure, great specific surface area (>900 m2/g), and strong adsorption, low surface energy PDMS was loaded into MCM-41 using the vacuum negative pressure method, and hydrophobically modified MCM-41 (MCM-41/PDMS) was produced; Subsequently, MCM-41/PDMS, epoxy resin, curing agent and diluent were blended to produce the superhydrophobic coating by using the blending method; finally, the coating was sprayed on the substrate surface to form the epoxy/PDMS/MCM-41 superhydrophobic coating by using a simple spraying method. In addition, by adjusting the ratios of MCM-41/PDMS and epoxy resin, an optimal balance of hydrophobicity and adhesion was obtained, and mechanical durability tests such as tape peel resistance test and abrasion resistance test were performed on the superhydrophobic coatings under this formulation.

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