Layer-by-layer membrane assembly: entropy, electrostatic interaction, hydrogen bond

The driving force for layer-by-layer (LbL) self-assembly of polyelectrolytes (PEs) has been misunderstood as mainly by electrostatic contribution, in combination with hydrogen bonding, and hydrophobic interactions. Entropy contribution has been raised but largely overlooked. This work demonstrated that neither electrostatic interactions nor hydrogen bonds can act as the sole driving force for LbL assembly; but both play a synergistic role with entropy increase as the essential driving force. With hydrophobic interaction, an intrinsic entropy driven phenomenon, we concluded that the assembly of PE is primarily entropy driven. Our understanding consolidates the scientific basis for designing LbL membranes with specific pore sizes, salt resistance and acid/base tolerance for ion separation, and organic compound removal.