Surface And Interface Engineering Of Polymer Membranes Via Polydopamine/Polvethvlene-Imine Co-deposition

Surface and interface engineering is an efficient approach to high-performance and multi-functional membranes.One of the most rencent and promising technologies is the mussel-inspired dopamine deposition.However,the conventional dopamine deposition suffers from the long deposition time,moderate hydrophilicity,poor uniformity and stability,limiting its further application in membrane applications.Herein,we developed a dopamine/polyethyleneimine(DA/PEI)co-deposition strategy to address these above issues.This technology shows great potential in controllable membrane surface modification,thin film construction and organic-inorganic interface regulation.The as-prepared membranes were employed in oil/water separation,CO2 immobilization,membrane distillation,and nanofiltration.Firstly,we developed DA/PEI co-deposition method and revealed its deposition mechanisms.DA reacts with PEI via Michael addition or Schiff-base reactions to form surfactant-like complex,which immigrates and deposits at the air/liquid or solid/liquid interfaces.Comparing with the conventional DA deposition,this method exhibits great improvement in depositing rate,uniformity,hydrophilicity,stability,and reusability on surface modification of polypropylene microfiltration membranes.We also investigated the effects of deposition conditions on the membrane performance,and achieved an optimized PEI molecular weight of 600 Da and DA/PEI ratio ranging from 1:1 to 2:1.Secondly,we developed a single-surface deposition strategy to fabricate Janus flat and hollow fiber membranes with asymmetric wettability.The directional transport of water droplet on the Janus membrane was investigated.The Janus flat membrane was applied as a bubbler in enzyme-assisted CO2 immobilization.The hydrophilic side,which is superaerophobic underwater,facilitates the bubble arising with small size,while the hydrophobic side reduces the operating pressure by trapping air into the pores.In addition,the Janus hollow fiber membrane was employed in direct contact membrane distillation.The asymmetric structure is helpful in reducing the mass transfer resistance without compromising the heat transfer resistance,leading to superior performance in membrane distillation.Secondly,we discovered and investigated the film formation at the air/water interface of DA/PEI solution,and demonstrated the asymmetric properties of the as-prepared free-standing films.We further fabricated a positively charged thin film composite membrane at the air/water interface with a sub-60 nm skin layer,and applied the membrane in nanofiltration.The fabrication conditions were also optimized in this research.Lastly,the PDA/PEI coating was employed as an intermediate layer for organic-inorganic composite fabrication via bio-inspired mineralization.Both SiO2 and ZrO2·nH2O mineralized membranes were prepared through this process.Such membranes shows excellent hydrophilicity and underwater superoleophobicity,which can separate oil-in-water emulsions with outstanding separation performance and oil repelling property.Moreover,ZrO2·nH2O mineral coating could enhance the membrane rigidity,resulting in improved mechanical and thermal stability.