A facile methodology to make the glass surface superhydrophobic
Graphical abstract
Introduction
Superhydrophobic phenomena are often found in nature, for example, lotus leaf, due to its high-water contact angle and low roll-off angle [1]. In general, the wettability of a surface is dependent on surface roughness and surface energy, which can be described by the Wenzel and Cassie-Baxter models [2] as follows:
Although, many researches have been coated nanoparticles/films on glass using some techniques [3], [4]. Their coating easily destroyed due to weak physical or chemical bonding between the coating and substrate, leading to loss of superhydrophobicity [5]. Recently, Meng Xu at el. have been focused on the fabrication of superhydrophobic surfaces using wet chemical etching processes [6]. Hydrofluoric acid (HF) etching can permanently improve the surface roughness due to simple, high etching rate and low-cost method. However, the limitation of wet chemical etching is uncontrolled in the reaction and the roughness in microscale [7]. Although it could increase the water contact angle followed by the Wenzel model, it could not demonstrate a low sliding angle followed by the Cassie-Baxter model. Therefore, a simple and cost-effective method to fabricate surfaces in nanoroughness remains a challenge, because surface roughness directly affected to hydrophilic –OH groups. Annealing process plays an important role in the changes in physical characteristics, such as glass crystallization, residual stress, strengths, thermal expansion, and hardness. Since it occurs at a lower temperature lower than the transition point [8], [9]. The combination of annealing and etching processes has been successfully applied to construct the superhydrophobicity to Cassie-Baxter models [6]. However, no research has focused on soda-lime silicate glass due to its low transition temperature, despite soda-lime silicate glass is the most important commercial glass with many applications [10]. In addition to surface roughness being an important factor, low surface energy also contributes to superhydrophobicity. Methlytrichlorosilane (MTCS) in particular has more chemical reactivity than others in the alkyltrichlorosilane group [11].
In this work, we aim to build on previous findings to solve common problems and improve the simple and cost-effective methods for imparting superhydrophobic properties on low-temperature glass surfaces. Simple annealing and etching techniques were used to increase the surface roughness of glass. The etched/annealed glass was then made superhydrophobic by dip-coating in Methlytrichlorosilane (MTCS).
Section snippets
Samples preparation
Glass surfaces were modified to be hydrophilic by cleaning microscope glass slides (10 × 30 × 1 mm3, SAIL BRAND, transition temperature 545 °C). Four conditions were tested in this research: bare glass slides (G), annealed glass at 100 °C for 1 h under atmospheric pressure (GA), etched glass with 6% v/v concentration of hydrofluoric acid (HF, 48% purity, EMSUE®) (GE), annealed and etched glass (GAE). MTCS solution with a concentration of 2.5% v/v (99% purity, Sigma-Aldrich) in toluene (99.5%
Results and discussion
Fig. 1(A, a) shows the microstructures of bare glass (sample G) with the mean roughness (Ra) of 0.21 nm. After annealing at 100 °C (Fig. 1(B, b)), the roughness was increased to 10.45 nm. It is worth noting that the annealing temperature has directly affected the thermal expansion, residual stress, and hardness leading to the change in nano-scale on the glass [9]. After etching, the roughness of sample GE (Fig. 1(C, c) was 53.98 nm, while the roughness of sample GAE (Fig. 1(D, d)) slightly
Conclusions
In summary, the glass surface was successfully modified using facile annealing and etching techniques. The annealing temperature not only reduces the residual stress but also reduces the hardness on the glass surface. Surface morphology and hydroxyl groups are the key points for controlling the morphology of the MTCS polysiloxane. Finally, surface roughness at different scales not only affects the formation of polysiloxane but also affects the superhydrophobicity following the Wenzel and
CRediT authorship contribution statement
Nidchamon Jumrus: Conceptualization, Methodology, Visualization, Formal analysis, Data curation, Writing - original draft. Thanakorn Chaisen: Conceptualization, Visualization, Methodology. Atchara Sriboonruang: Validation. Arisara Panthawan: Validation. Tewasin Kumpika: Validation. Ekkapong Kantarak: Methodology. Pisith Singjai: Resources, Investigation. Wiradej Thongsuwan: Conceptualization, Visualization, Formal analysis, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was supported by The Science Achievement Scholarship of Thailand, The Graduate School Chiang Mai, Center of Advanced Materials for Printed Electronics and Sensors Materials Science Research Center and Department of Physics and Materials Science, Faculty of Science, Chiang Mai University.
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