Robust fabrication of fluorine-free superhydrophobic steel mesh for efficient oil/water separation

Qing Wang a, Mingguang Yu b, Guangxue Chen a†, Qifeng Chen a, Junfei Tian a

aState Key Laboratory of Pulp & Paper Engineering, South China University of Technology, Guangzhou 510640, China

bSchool of Materials Science and Energy Engineering, Foshan University, Foshan528000, China

† Corresponding author. Prof., Ph.D.; Tel.: 020-22236485; Fax: 020-22236485;

E-mail address: (G.X. Chen).

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Supplementary Text

Fig. S1

Influence of weight ratio of dual sized particles to the hierarchical structure

In order to investigate the weight ratio of dual sized particles to the hierarchical structure, we made the following experiments. We measured the water contact angle of films composed with dual sized PS@SiO2@HDTMS particles with different weight ratios (a: m~1um/m~200nm=1:2; b: m~1um/m~200nm=1:1; c: m~1um/m~200nm=2:1). Seen from Fig.S1, when the weight ratio was 1:2, the micro-sized particles were buried under the nano-sized particles, the nano-particles accounted for the main part of the film. The corresponding water contact angle was 143°. When the weight ratio increased to 1:1, the film showed multi-scales hierarchical structure and the water contact angle increased to 159°. When the weight ratio further increased to 2:1, the film was dominated by the micro-sized particles and the water contact angle was 155°.

This can be explained by the Cassie-Baxter equation: cos θr = f1cosθs − f2

where f1 and f2 represent the fractions of solid surface and air incontact with water (f1 + f2 = 1). θr represent the contactangle of a water droplet on the rough surface, while θs represent the contact angle of a water droplet on a smooth surface [1].

According to the Cassie-Baxter equation, as water droplet cannot wet the glass film completely, air can be trapped in the hollows between the water droplet and the film [2]. The droplet interacts with the hierarchical structured surface that consists of solid materials and air pockets. Based on this Cassie–Baxter equation, increasing the fraction of air (f2) is able to increase the water contact angle on the rough surface. So the SEM images combine with the water contact angle clearly showed that moderate weight ratio of micro-sized to nano-sized PS particles can be attributing to this multi-scaled hierarchical structure and significantly improve the hydrophobicity.

Fig. S1. SEM and corresponding water contace angle of films consist of different weight ratio of dual sized particles: (a) m~1um/m~200nm=1:2; (b) m~1um/m~200nm=1:1; (c) m~1um/m~200nm=2:1.

Influence of porosity to permeation of the mesh layer

In this study, the steel mesh we used for oil/water separation was 200/ inch with oil/water separation rate of 30s. We also measured the oil/water separation rate of the modified mesh film with 100/inch and 400/inch (500mL, v/v, 1/1). Seen from Online Resource 4, when steel mesh with 100/inch was used, the red-dyed chloroform quickly spread and permeated through the modified mesh and rapidly dropped into the conical flask below within 20s. However, certain amount of methylene blue dyed water also dropped into the conical flask possibly because the pore was too large to prevent water from permeating through the mesh film. When mesh film with 400/inch was used (see Online Resource 5), the oil/water mixture could be separated within 90s, which also showed fast oil/water separation rate. So the change in porositycould influence the permeation of the mesh layer. The steel mesh with 200/inch was the optimum separation layer because it provided excellent supperhydrophobic/superhydrophilic property and sufficient oil/water separation ability.

References:

1. Li Z, Wu C, Zhao K, Peng B, Deng Z.(2015) Polydopamine-assisted synthesis of raspberry-like nanocompositeparticles for superhydrophobic and superoleophilic surfaces. Colloid SurfAPhysicochemEng Asp470 : 80–91

2. Chen B, Qiu J, Sakai E et al (2016) Robust and Superhydrophobic Surface Modification by a "Paint+Adhesive" Method: Applications in Self-Cleaning after Oil Contamination and Oil-Water Separation. ACS Appl. Mater. Interfaces 8:17659−17667