Another important advantage of spin assembly is that the film formation process is not solely dependent on electrostatics to induce deposition. The linear growth of a PAZO layer over 10 deposition cycles on top of a single positively charged PEI underlayer has been reported . A thick PEI layer on a bare, negatively charged substrate using 10 deposition cycles of 10 Mm PEI was also built . Whereas film formation in the case of ionic self-assembly is governed by electrostatics and entropy; the underlying mechanism for film formation in spin-assembly involves the mechanically induced entanglement between polyelectrolyte chains of different layers. Electrostatics, therefore, takes a supplementary role in spin-assembly, enhancing the deposition process when alternating charges are used. Single-species multiple deposition do not show linear growth when carried out using conventional dipping techniques .
In summary, a new ultra-thin film-forming process, spin-assembly, is an excellent method for controlling the amount and thickness of adsorbed polyelectrolyte in fabricating multiplayer thin film with highly ordered internal structure far superior to the structure obtained with the dip SA process. It also allows us to build multiplayer polyelectrolyte multilay-ered films without the absolute requirement of alternating charges.
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