Hydrophobic Waterproof Smart Surface Coatings

Aerogel-Silica-Based Superhydrophobic Water-Repellent Smart Surface Coatings

Abstract

In this study, homogeneous coatings were applied to glass and nanofiber membranes obtained via electrospinning using the dip-coating technique with aerogel and silica product mixtures, rendering the materials superhydrophobic and water-repellent. Through integration of these coatings into industrial-scale production, various product ranges with functional application possibilities can be obtained.

1. Introduction

Surface treatments are based on classical and modern technologies applied to modify water retention, mechanical and thermal properties of material surfaces or for aesthetic purposes. Different physical or chemical coating technologies can be used to improve surface properties that a material surface does not possess or possesses only minimally [1,2]. In surface coatings, water-repellent properties are the most frequently preferred characteristic. The ability of nonpolar molecular structures to behave as complementary molecules in similar intramolecular interactions or in aqueous environments is the hydrophobic (water-repelling) effect. Through the hydrophobic effect, a shielding property is created that prevents the formation and approach of water [3,4]. The dip-coating technique, frequently preferred as a hydrophobic coating method, is commonly used. This technique consists of a material holder apparatus that moves up and down in a defined cycle and a mixture container that can hold solution below. The method involves immersing and withdrawing the material to be coated in the solution mixture prepared in the cycle entered through the device, providing coating [5,6]. In recent years, aerogel products with popular applications are used in water-repellent applications due to their superhydrophobic structure. When literature studies in this field are examined, aerogel-based work has been conducted on different coating technologies and studies have demonstrated the water-repellent potential [7-9]. Aerogel material is a solid substance in which the liquid component in a gel has been replaced with air. Aerogel material is used in many areas such as thermal insulation, acoustic insulation, space and aviation applications, catalysts and catalyst supports, fuel cells, chemical sensors, drug delivery systems, and window applications. Scientists have named aerogel "frozen smoke." In addition to being bulletproof, it can withstand the blast from 1 kilogram of dynamite and can protect against temperatures up to 1,300°C and cold down to -120°C [10,11]. As another water-repellent material like aerogel, silica material is used. Silica is a silicon oxide with the chemical formula SiO₂, found in nature most commonly as quartz and in various living organisms. In many parts of the world, silica sand is a main component. Literature reviews have examined silica-based hydrophobic surface coatings. When water-repellent potential was investigated, while there was repellent property for a certain period, water-repellent potential decreased over increasing time periods. Thus, the need for new material searches and blend mixture materials increased. Since aerogel products also had compatibility issues, new materials were mixed on coating surfaces to achieve interfacial compatibility between the coating surface and the coating material [12,13]. Electrospinning technology is the production of nanofiber membranes from polymer solutions with the aid of an electrical field. It is a simple, low-cost system that enables the production of functional materials. Nanofiber structure is defined as one thousandth of a human hair thickness [14-16]. In this study, both the individual water-repellent properties of aerogel and silica coating agents and the coating properties between the materials were improved through composite mixture materials applied to glass and nanofiber membrane surfaces using the dip-coating technique. Thus, superhydrophobic smart surface coating products with high water-repellent potential were obtained.

2. Material and Method

2.1. Material

Aerogel and silica materials were obtained from local suppliers. Deionized water, dimethylformamide (DMF), chloroform and polycaprolactone (PCL) with a molecular weight of 80,000 g/mol from Sigma/Aldrich brand were used. In the electrospinning technique, oil paper was preferred as the substrate surface.

2.2. Method

Production of Superhydrophobic Water-Repellent Smart Surface Coating

Prior to the electrospinning technique, 10 grams of PCL in a solvent system with a 60/40 chloroform/DMF mixture was dissolved in a magnetic stirrer by heating to 55°C for 60 minutes. Nanofiber membranes were obtained by electrospinning on oil paper at room conditions with a feeding rate of 3 milliliters per hour, 30 kV voltage, and a distance of 20 cm between the syringe and collector. To enable homogeneous coating of aerogel and silica materials, they were first frozen with liquid nitrogen in a ball mill and then ground to a size of 100 micrometers. The obtained powders were blended in a 50-50 ratio and the dry mixture was placed in 100 ml of deionized water to achieve a homogeneous mixture. This mixture solution was subjected to repeated immersion and withdrawal cycles in the dip-coating technique to provide homogeneous coating and then dried in a vacuum oven at room temperature. The production stages of superhydrophobic water-repellent smart surface coating are shown in Figure 2.1. [caption id="attachment_133696" align="aligncenter"] Figure 2.1. Production stages of superhydrophobic water-repellent smart surface coating[/caption]

3. Results and Discussion

Nanofiber membranes and glass surfaces obtained by electrospinning were homogeneously coated with an aerogel and silica mixture using the dip-coating technique. Morphological images of the obtained nanofiber membranes were captured using a scanning electron microscope (SEM). Figure 3.1 shows the nanofiber membrane and SEM image. The obtained nanofiber diameter distribution ranges from 180 to 380 nm. [caption id="attachment_133698" align="aligncenter"] Figure 3.1. Membrane and SEM image[/caption]

4. Conclusions

In this study, products containing an aerogel and silica mixture were successfully applied to glass and electrospun nanofiber membranes using the dip-coating technique to provide homogeneous coating. The mixture coated on the obtained glass and nanofiber membrane surfaces was observed to repel water excellently. Considering the functional application potential of the produced products, with their water-repellent, thermal insulation and durability properties, they can be ideal materials for targeted use in many sectors in the industrial field.

References

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Erdi Buluş Metallurgical and Materials Engineer Senior Materials Technology Specialist İstanbul Arel Üniversitesi ArelPOTKAM (Polymer Technologies and Composite Application and Research Center)

Gülseren Sakarya Buluş Specialist Nurse Silivri District Health Directorate Bahçeşehir Üniversitesi Graduate Education Institute Engineering Management Thesis-Based Master's Program