Superwettability-based separation

The separation of mixtures is of significant value in both research and industrial applications. Separation processes convert the mixture or solution of different chemical substances into individual constituents forming the mixture. To date, many separation techniques have been developed to achieve various separation functions. For example, the superwettability-based process has been widely used to separate oil/water mixtures due to their different wetting behaviors. Unfortunately, this approach is more appropriate for simple oil/water separation and less effective for separating underwater bubbles and mixtures of liquid polymers and water. Therefore, considering the rapid technological advancement and growing application of polymer materials, developing effective and efficient polymer/water and bubble/water separation strategies is highly desirable.

Research has revealed that water/oil mixtures can be efficiently separated by porous materials with either underwater superoleophobicity or superhydrophobicity properties. Previously, superwetting states related to underwater polymers and bubbles were developed. They include underwater superpolymphobicity and superaerophobicity that function in a manner similar to the oil repellence of the underwater superoleophobic surfaces in that the superpolymphobic and superaerophobic materials repel the liquid polymers and bubbles, respectively. This is an indication that superwetting materials can potentially be applied to separate liquid polymers and tiny bubbles from water even though this area has remained largely underexplored.

In a recent study by Xi’an Jiatong University scientists at School of Electronic Science and Engineering: Professor Jiale Yong, Professor Qing Yang, Dr. Jinglan Huo, Professor Xun Hou, and Professor Feng Chen used the wettability-based oil/water separation strategy to separate the mixtures of liquid polymers and water as well as that of bubbles and water. The aim was to extend the scope of applications of the well-developed wettability separation method. Their research work is currently published in the journal, Nano Select.

In their approach, the authors relied on the special surface wettability properties of the separation materials to achieve the expected results. The micro/nanostructures were produced on a stainless-steel mesh via femtosecond laser treatment to endow the mesh with desirable properties. The feasibility of separating the liquid polymers and bubbles from water using the as-prepared superwetting mesh was experimentally verified.

The results showed that the superwetting mesh exhibited underwater superoleophobicity, superpolymphobicity and superaerophobicity properties attributed to the formation of the laser-induced microstructures. For instance, a CA of 154.8°, 156.3°, and 153.7° was recorded for the small oil droplet, polymer droplet, and bubble on the structured mesh in water, respectively. As such, the resulting mesh exhibited strong repellence to oils, liquid polymers, and bubbles in the water medium. Moreover, water penetrated the structured mesh due to the superhydrophilicity while oils, bubbles, and liquid polymers got intercepted due to their repellence of the laser-induced microstructures. This phenomenon allowed the successful separation of oils, liquid polymers, and bubbles from the water with a high separation efficiency. In addition, it was worth noting that the presented separation method based on superwettability demonstrated potential application in separating various liquid-gas and liquid-liquid mixtures.

In a nutshell, the study reported an extension of superwettability-based oil/water separation method to separate polymer/water and bubble/water mixtures. The resulting laser-treated mesh exhibited remarkable superoleophobicity, superpolymphobic and superaerophobic properties desirable to achieve the various separation processes. By taking advantage of the different wetting behaviors of the mesh to oils, polymers, and bubbles, the presented method successfully separated the oils, liquid polymer, and bubble from the water with a high separation efficiency. Apart from separating oil, polymers and bubbles from water, the as-prepared superwetting mesh also demonstrated potential applications in separating various liquid/liquid and liquid/gas mixtures. Altogether, first author, Professor Jiale Yong in a statement to Advances in Engineering, pointed out that the diversified wettability-based separation process is a promising separation method for numerous applications, including energy utilization, environmental protection, and industrial manufacturing.