Superhydrophobic Zr-based metallic glass surface with high adhesive force
Ning Li,1,a) Ting Xia,1 Liping Heng,2 and Lin Liu1,a) 1
School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074,
People’s Republic of China Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, People’s
Republic of China
Supplementary Material for surface energy difference between two BMGs
To reveal the possible mechanism that responsible for the different water contact angles between the Zr- and the Pd-based MG, the essential CAs of the two MGs’ surface (polished to mirror surface with roughness about 9 nm, as described in figure 5a) are measured by deionized water. Figure 5 (b) presents a hydrophobic Pd-based MG surface with CA of about 98.8±0.8°, while the Zr-based MG surface with a relatively small CA of about 82.5±0.9°, as described in figure 5 (c), shows a hydrophilicity. To further analyze this difference, CAs are measured by methylene iodide and the surface free energies (SFEs) of the two MGs are calculated according to the following eqution:31, 32 1/ 2 1 c os 2sd ld
2 p s
1/ 2 p l
where is the contact angle, l is the SFE of the liquid used in the measurements, the superscripts d and p refer to the dispersion force and hydrogen bonding (one of polar terms) components, s is the SFE of the solid MG sample, which can be calculated as: a)
Authors to whom correspondence should be addressed. Electronic address: [email protected]
and [email protected]
(Lin Liu). 1
s sd sp
The properties of the both deionized water and methylene iodide can be obtained from Ref. 31. According to equation (3), surface free energies of both MGs are calculated and the results are listed in Table II. The dispersion forces ( sd ) of two MGs are almost identical, while the polar term (corresponding to hydrogen bonding, sp ) of the Zr-based MG (3.5±0.4) is much larger that of the Pd-based MG (0.19±0.07), indicating that there is a more tendency of the Zr-based MG surface to interact with surrounding small molecules33, what is the main reason for the hydrophilic Zr-based MG surface with a higher surface free energy by comparing with the Pd-based MG surface.
FIG. 5. The 3D profile of the smooth BMG surface (a); the essential contact angles on the Pd- (b) and the Zr-based (c) MG surfaces. 2
Table II Surface free energy (SFE) of both Zr- and Pd-based MGs.
Contact angle (º)
Surface free energy (mJ/m2)
sd , Dispersion force component of the surface free energy. sp , Hydrogen bonding (one of polar terms) component of the surface free energy.
s , Surface free energy of the solid MG.