Electric Field Directed Codeposition Of Polvdopamine/Polvelectrolvte And Its Functional Applications

Mussel-inspired chemistry has attracted much attention due to the oxidative polymerization of dopamine and the versatile formation of universal polydopamine(PDA)coatings on various substrates.It is very interesting that these mussel-inspired PDA coatings have a series of functional groups including catechol,amine,and imine,which can be further used for chemical reaction or post-modification.Therefore,PDA coatings play a crucial role in the chemical modification of material surface.However,dopamine polymerization oxidized by air is very slow,leading to a tedious process from ten hours to a few days,and the PDA aggregates will deposite nonselectively on the material surfaces and on the vessel walls at the same time,which result in inefficient utilization of dopamine and the environmental disruption.All these shortages will restrict its wide applications in practical use and industrial production.Polydopamine-based coatings were fabricated via an electric field-accelerating and-directing codeposition process of polydopamine with polyelectrolyte such as polycations,polyanions,and polyzwitterions.The coatings are uniform and smooth on various substrates,especially on those adhesion-resistant materials including poly(vinylidene fluoride)and polytetra-fluoroethylene membranes.Compared with other self-polymerization enhanced methods,this approach has higher deposition rate by promoting the diffusion/movement of PDA-based aggregates,and they can deposite orientedly and selectively on the desirable surface.Besides,we have suggested the electric field acceleration mechanism at the cathode and the oxygen promotion mechanism at the anode by comparing the chemical composition,roughness,morphology,and hydrophilicity of the codeposited surfaces at different places in the electric field.Moreover,this electric field-directed deposition method can be applied to broaden the functional PDA-based codepositon systems as well as facilely prepare Janus membranes with asymmetric chemistry and wettability,which is promising for various applications.To further investigate the functional applications,Janus microfiltration membranes with ca.340 nm pore size were prepared via the one-step electric field directed codeposition of PDA/poly(diallyldimethylammonium chloride)(PDDA)and can be used to separate oil-in-water nanoemulsions with oil diameter of 20-100 nm.The as-prepared membrane is hydrophilic on one side and hydrophpbic on the other.Nanoemulsions can be demulsified on the hydrophilic side effectively by the electrostatic interaction of PDDA,and then the coalesced oil droplets are spontaneously transferred to the hydrophobic side due to the extraordinary irreversible transport property on the Janus surface.The separation performance is unparalleled with high separation efficiency and oil permeation flux.And this novel membrane exhibits excellent reusability property,endowing it with steady flux during the continually treatment process.Besides,the functional layers can be replaced to other charged polymers and used in various fields such as anti-fouling surface and fog collection.