Polyamide Membranes With Turing Strctures Formed Via Interfacial Polymerization

Spatiotemporal stationary structures that emerge in reaction-diffusion systems maintained far from thermodynamic equilibrium were predicted more than 60 years ago by Alan Turing as a prototype for pattern formation in living systems.Over the past 30 years,a variety of two-and three-dimensional stationary structures have been discovered in chemical and biological systems.However,designing Turing structures and developing their potential applications are notoriously difficult.Inspired by these works,we report a facile route based on interfacial polymerization to generate polyamide membranes with Turing structures.Main content of this thesis includes the following three aspects:(1)Design polyamide membranes with Turing structures:The polyamide membranes formed by a conventional interfacial polymerization reaction is not of Tuirng-type,for there are not appropriate differences between the diffusion coefficients of amine and acyl chloride.When a certain amount of macromolecule,PVA,was added to the aqueous solution,it interacts with the activator via hydrogen bonding and increases the solution viscosity,further reducing the difusion rate of the amine,leading to diffusion-driven instability and generate polyamide memrbanes with Turing structures.Atomic force microscopy measurements show that the surfaces of membranes with spots or stripes Turing structures are quite different from that of traditional polyamide membranes.To further investigate the Turing structures,the membranes were characterized by scanning electron microscopy and compared the results to transmission electron microscopy analyses.The images show that the Turing structures are bubble or tube shape in three-dimensional,like the Turing patterns in other chemical systems.(2)Evaluate the separation performance of Turing-type polyamide membranes.Next,we evaluated separation performance of the two membranes using cross-flow filtration and explored structure-property relationships in such membranes for desalination applications.The data show that Turing-type membranes exhibit excellent separation performance,surpassing the water-salt separation limitation of traditional desalination membranes.Counterintuitively,water permeability and water-salt selectivity are both high,in contrast to the behavior of traditional polymer membranes,where higher water permeability invariably leads to lower water-salt selectivity.The water flux of tube structure membrane is as high as 125 L/m2.h at 4.8 bar and 25℃,exhibits higher water fluxes and similar salt rejections compared to that of traditional polyamide membranes under the same filtration conditions.Based on the observations,we hypothesized that there must be some specific sites with relatively higher water permeability in the Turing structures,these high permeability sites lead to the membranes with enhanced water transport properties.(3)Explore structure-property relationships in Turing-type polyamide membranes.To verify this assumption,we use gold nanoparticles as probes for the detection of the spatial distribution of water permeability sites in the Turing-type polyamide membranes.During the filtration,the water flow carries the nanoparticles depositing on the membrane,where they would serve as reference markers providing spatial evidence of the water permeability distribution over the membrane surface.Electron micrographs revealed that the deposition of the nanoparticles was not uniformly distributed over the membrane surfaces.Most of the nanoparticles are deposit around bubble or tube structures,which provide a visual evidence supporting the existence of relatively higher water permeability sites in the Turing structures.Our work demonstrates Turing structures can be produced in the interfacial polymerization reaction when appropriate initial conditions are created.Microscopic characterization of the membranes reveals that the spatial distribution of relatively higher water permeability sites agrees well with the corresponding Turing structures at the nanoscale.These unusual structures,which generated by diffusion-driven instability,enable outstanding transport properties in both water permeability and water-salt selectivity.