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. 2025 Apr 19;30(8):1840.
doi: 10.3390/molecules30081840.

Construction of a Covalent Crosslinked Membrane Exhibiting Superhydrophilicity and Underwater Superoleophobicity for the Efficient Separation of High-Viscosity Oil-Water Emulsion Under Gravity

Mengxi Zhou  1 , Peiqing Yuan  2 , Xinru Xu  1 , Jingyi Yang  1
Affiliations

Construction of a Covalent Crosslinked Membrane Exhibiting Superhydrophilicity and Underwater Superoleophobicity for the Efficient Separation of High-Viscosity Oil-Water Emulsion Under Gravity

Mengxi Zhou et al. Molecules. .

Abstract

The separation of high-viscosity oil-water emulsions remains a global challenge due to ultra-stable interfaces and severe membrane fouling. In this paper, SiO2 micro-nanoparticles coated with polyethyleneimine (PEI) were initially loaded onto a stainless steel substrate. This dual-functional design simultaneously modifies surface roughness and wettability. Furthermore, a covalent crosslinking network was created through the Schiff base reaction between PEI and glutaraldehyde (GA) to enhance the stability of the membrane. The membrane exhibits extreme wettability, superhydrophilicity (WCA = 0°), and underwater superoleophobicity (UWOCA = 156.9°), enabling a gravity-driven separation of pump oil emulsions with 99.9% efficiency and a flux of 1006 L·m-2·h-1. Moreover, molecular dynamics (MD) simulations demonstrate that the SiO2-PEI-GA-modified membrane promotes the formation of a stable hydration layer, reduces the oil-layer interaction energy by 85.54%, and exhibits superior underwater oleophobicity compared to the unmodified SSM. Efficiency is maintained at 99.8% after 10 cycles. This study provides a scalable strategy that combines covalent crosslinking with hydrophilic particle modification, effectively addressing the trade-off between separation performance and membrane longevity in the treatment of viscous emulsions.

Keywords: crosslinking; emulsion separation; molecular dynamics simulation; superwetting membrane; underwater superoleophobic.

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Conflict of interest statement

The authors declare no conflicts of interest.

Figures

Figure 1
Figure 1
SEM images: (a) SSM; (b) SSM@SiO2-PEI; (c) SSM@SiO2-PEI-GA.
Figure 2
Figure 2
The EDS results and mapping: (a) SSM@SiO2-PEI; (b) SSM@SiO2-PEI-GA.
Figure 3
Figure 3
AFM images (2D and 3D): (a) SSM; (b) SSM@SiO2-PEI; (c) SSM@SiO2-PEI-GA.
Figure 4
Figure 4
FTIR spectra of SSM, SSM@SiO2-PEI, and SSM@SiO2-PEI-GA.
Figure 5
Figure 5
(a) XPS survey spectra of SSM, SSM@SiO2-PEI, and SSM@SiO2-PEI-GA; (b) high-resolution XPS N 1s, C 1s, and Si 2p spectra of SSM@SiO2-PEI; and (c) high-resolution XPS N 1s, C 1s, and Si 2p spectra of SSM@SiO2-PEI-GA.
Figure 6
Figure 6
The water contact angles: (a) SSM; (b) SSM@SiO2-PEI; (c) SSM@SiO2-PEI-GA. The underwater oil contact angles: (d) SSM; (e) SSM@SiO2-PEI; (f) SSM@SiO2-PEI-GA.
Figure 7
Figure 7
Separation efficiency and flux of SSM, SSM@SiO2-PEI, and SSM@SiO2-PEI-GA.
Figure 8
Figure 8
(a) Photograph of feed emulsion; (b) optical microscopy image and oil droplet size distribution of feed emulsion; (c) photograph of filtrate; and (d) optical microscopy image of filtrate.
Figure 9
Figure 9
(a) Separation efficiency of different oils in the emulsions using SSM@SiO2-PEI-GA; (b) separation flux of different oils in the emulsions using SSM@SiO2-PEI-GA.
Figure 10
Figure 10
Reusability of SSM@SiO2-PEI-GA for pump oil emulsion.
Figure 11
Figure 11
(a) The total energy of different models at different times. (b) The calculated EOil/Layer of different models at different times. (c) Snapshots of the oil/water-SSM@SiO2-PEI-GA model at different times. (d) Snapshots of the oil/water-SSM@SiO2-PEI model at different times. (e) Snapshots of the oil/water-SSM model at different times.
Figure 12
Figure 12
Mechanism of oil–water emulsion separation.
Figure 13
Figure 13
Preparation of SSM@SiO2-PEI-GA.
Figure 14
Figure 14
Schematic diagram of the emulsion separated by a membrane.
See this image and copyright information in PMC

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