It was learned from Zhejiang University that the team of Professor Zhang Lin from the School of Chemical Engineering and Bioengineering of Zhejiang University, who has long been engaged in membrane science research, has combined the studies of Turing and membranes to create a nanometer-scale Turing structure on a thin film for the first time. This research result for the first time to construct the Turing structure for the application field was published in the top international journal "Science" on May 4th, Beijing time.
The black and white stripes of the zebra, the spiral threads of the conch, the curling of the plant's stems and leaves... The formation of these regularly-repeated patterns in nature has always been an intriguing problem. Back more than 60 years ago, the British scientist Turing had Predictions: Some repetitive natural patterns may be generated by the interaction or action of two specific substances (molecules, cells, etc.). Through a process that he calls 'reaction-diffusion', these two components will spontaneously Self-organized into stripes, stripes, rings, spirals or mottled spots and other structures. Later scientists confirmed this conjecture, and this type of structure is called 'Turing structure'.
Interfacial polymerization The preparation of ultrathin separation membrane technology has been used since the advent of the 1980s. It is quite mature, but both the preparation process and the reaction mechanism of the nanofiltration membrane and the reverse osmosis membrane prepared by the interfacial polymerization are the same, but the surfaces of both are The structure is quite different: the surface of the nanofiltration membrane is smooth, and the surface of the reverse osmosis membrane has a peak-valley structure, which is relatively rough. Zhang Lin team conducted in-depth research. When digging into the causes of differences, they found that the interfacial polymerization process is a typical 'reaction-diffusion' process. ' System.
The necessary condition for the Turing structure is that the difference between the diffusion coefficients of the two reactants must be more than one order of magnitude. The research team wanted to find a way to change the difference in the diffusion coefficient of the reactants so that it could satisfy this condition.
After careful analysis and discussion, the research team proposed adding hydrophilic macromolecules that hinder the diffusion of reactants in the aqueous solution of the reactants with a small diffusion coefficient. This work is like pulling the 'thigh' of the slow diffusion of the reactants. Let it be Running a little slower. In a large number of experiments, researchers tried to add various hydrophilic macromolecules to reduce the rate of diffusion of the water-soluble reactants into the oil, and on the interface between water and oil, and The reactants in the oil react to form a novel nanofiltration membrane with a periodically changing Turing structure.
After a long period of continuous experimentation, researchers found that polyvinyl alcohol works best as a hydrophilic macromolecule that inhibits the diffusion of reactants.
With the 'hindering' effect of polyvinyl alcohol on the diffusion of the reactants, the otherwise smooth and smooth film surface literally 'long' out the Turing structure. These are only 20-30 nm dense, periodic regular Turing structures. Some are tubular and some are blister-like, providing membranes with sites that allow more water to pass through the membrane surface, which in turn enhances the membrane's water permeability.
If viewed through an electron microscope, these Turing structures are like a semi-circular tent densely covering the surface of the membrane. These 'spreading' bulging 'tent structures' have many voids in between, reducing water penetration. Over-resistance makes the separation performance of the membrane 3 to 4 times higher than that of the membrane prepared by the conventional preparation method. That is, the water passing through the membrane is 3 to 4 times more than the original, which greatly reduces the production of water in the membrane process. Cost, improve the separation efficiency.
The interfacial polymerization of nanofiltration membranes usually takes less than a minute to complete, and the traditional test method for the change of the diffusion rate after the addition of hydrophilic macromolecules is almost out of order. Eventually the researchers performed characterization by nuclear magnetic resonance. After the addition of hydrophilic polymer, the diffusion rates of the two reactants were poor, and it was verified that the experiment successfully produced a novel separation membrane with a Turing structure.
For this study, three paper review experts gave a high rating. One of the review experts believe that this is a very interesting new type of desalination film. 'As far as I know, this is the first time I have tried on the film. Manufacturing Nano-scale Turing Structure Report.