SUPPORTING INFORMATIONfor

Study on the oil/water separation performance of a super-

hydrophobic copper mesh under downhole conditionsYao Lu1, 2, Zhe Li1, Gebremaniam Hailu1, Derong Xu1, Hairong Wu1,*, Wanli Kang1, 3,*

1 Research Institute of Enhanced Oil Recovery, China University of Petroleum (Beijing), Beijing, P.R. China 102249

2 Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta, Canada T6G 2W2

3 School of Petroleum Engineering, China University of Petroleum (East China), Qingdao, Shandong, P.R. China 266580

* Corresponding authors: Wanli Kang, e-mail: kangwanli@126.com, Tel.: +86-13589332193; Hairong Wu, e-mail: hrwu@cup.edu.cn, Tel.: +86-15010260120.

Structural characterization of super-hydrophobic copper mesh

X-ray diffraction (XRD) patterns were obtained with a multipurpose X-ray diffractometer

(D8 Advance, Bruker AXS Inc., Germany) using Cu Kα radiation with a scanning range of 2θ at

the rate of 2°/min. Energy dispersive spectrometer (EDS) spectrum and elemental mapping were

conducted using EDS detector equipped on Hitachi S-4800.

XRD patterns of the copper mesh before and after the oxidation process are shown in

Fig.S1a. It can be seen that both original copper mesh and the oxidized copper mesh show strong

XRD peaks of cubic-phase Cu according to JCPDS 77-3038, and the latter exhibits some new

diffraction peaks that can be well indexed to Cu(OH)2 according to JCPDS 35-0505. Therefore,

the nanoneedles grown on the surface of the copper mesh consists of Cu(OH) 2 nanocrystal. The

EDS spectrum of copper mesh modified by stearic acid is shown in Fig.S1b. The existence of C

peak suggests that OH- groups on the Cu(OH)2 surface graft with steric acid molecules containing

carboxyl groups via acid-base reaction. The steric acid with low surface energy is coated onto the

surface of Cu(OH)2 nanoarrays. The element O is derived from carboxylic acid groups of stearic

acid and generated Cu(OH)2 nanoarrays while Sn, Al and other metallic elements are derived from

the original phosphor copper material.

Fig.S1 (a) XRD patterns of the copper mesh before and after construction of Cu(OH)2

nanostructure; (b) EDS spectrum of the as-prepared Cu(OH)2 surface modified by stearic acid.

Microstructure of mesh modified by different concentration of stearic acid

An excessively high concentration of coated modifier will mask the initial gas space formed

by those nanoneedle structures, leading to the decrease of surface roughness (see Fig.S2b), which

is the key factor for constructing a super-hydrophobic surface. An ideal coating state is shown in

Fig.S2a, where stearic acid is attached to the surface of Cu(OH)2 nanoneedles as a thin film,

reducing its surface energy without affecting the roughness of the copper mesh.

Fig.S2 SEM images of the surfaces of the copper mesh with nanoneedles after immersing in (a) 50 g·L-1 and (b) 70 g·L-1 of stearic acid for 25 min.

The indoor simulation device and corresponding separation process

Fig.S3 shows the images of the indoor simulation device and the corresponding separation

process. It can be seen that when the oil/water mixture was pumped and lifted in the separator, the

crude oil could pass through the mesh into the measuring cylinder directly and quickly while

water was prevented from wetting the mesh. Thus, the oil/water separation in the lifting process of

produced fluid was realized.

Fig.S3 (a) The evaluation system of oil/water separation system, (b) the oil/water mixture for separation, (c) adding the mixture into intermediate container before separation, (d) the separation

process.Effect of salt and temperature on the separation performance

To investigate effect of water property on the separation performance of the copper mesh, the

mesh is immersed in the aqueous solutions with various salinities for 20 min before the separation

process. The effect of concentration of NaCl and CaCl2 on the separation rate (Qo) and the

separation efficiency (ηo) is presented in Fig.S4a and Fig.S4b, respectively. It is found that in a

wide range of salt concentrations, the Qo and ηo values remain almost unchanged, indicating that

the rough structure on the mesh has not been destroyed and there is no obvious reaction between

salts and stearic acid attached on the surface of the rough structure with addition of NaCl or CaCl2.

Fig.S5 shows the effect of the temperature on the separation performance of copper meshes

after being heated in the oven for 24 h. As the temperature reaches 120 °C, the separation rate and

the separation efficiency both decrease. This could be attributed to the desorption of the stearic

acid from the Cu(OH)2 nanoarrays owing to the excessive temperatures. It should also be noted

that within the normal reservoir temperature range (40-90 °C), the meshes can maintain a high

separation rate and separation efficiency, indicating that the meshes can well perform in the

wellbore for oil production operations.

Fig.S4 Effect of concentration of (a) NaCl and (b) CaCl2 on the oil separation rate and separation efficiency of copper meshes.

Fig.S5 Effect of temperature on the separation performance of copper meshes.

Varation of WCA after air exposure

Fig.S6 shows the relationship between the exposure time to air and the WCA of the super-

hydrophobic copper mesh. It is evident that the WCA of the copper mesh keeps almost unchanged

for two months, indicating that the copper mesh has good long-term stability in air.

Fig.S6 WCA of the super-hydrophobic copper mesh after air exposure for various aging time.