Speedy fabrication of free-standing layer-by-layer multilayer films by using polyelectrolyte complex particles as building blocks

A novel method for speedy fabrication of free-standing layer-by-layer (LbL) multilayer films in salt free media, and without the need for a sacrificial sublayer is described by using two different polyelectrolyte complex (PEC) nanoparticles as LbL self-assembly building blocks. Negatively charged polyelectrolyte complex particles (PEC⁻) consisting of poly(diallyldimethylammonium chloride)/sodium carboxymethyl cellulose (PDDA/CMCNa), and positively charged polyelectrolyte complex particles (PEC⁺) consisting of PDDA/poly(sodium-p-styrenesulfonate) (PDDA/PSSNa) were prepared and characterized by FT-IR, zeta-potential (ζ potential) and transmission electron microscopy (TEM). The LbL self-assembly of PEC⁺/PEC⁻ and PDDA/PEC⁻ was followed by quartz crystal microbalance (QCM), optical transmittance, UV-vis absorption spectroscopy and atomic force microscopy (AFM). QCM results show that the thickness growth rate of the PEC⁺/PEC⁻ pair is 9 times faster than that of the PDDA/PEC⁻ pair and this result is also supported by optical transmittance and UV-vis absorption. A robust free-standing multilayer film of (PEC⁺/PEC⁻)₂₅ can be easily peeled off from the substrate after being cross-linked in 3.5 wt% glutaraldehyde (GA) (80 °C, 50mins). Field emission electron scanning microscopy (FESEM) indicates that both the surface and cross-section of the multilayer film display layered structures. Furthermore, multiwall carbon nanotubes (MWCNTs) can also be uniformly incorporated into the free-standing LbL multilayer film by pre-incorporating MWCNTs into PEC⁻ particles. The experimental results show that using oppositely charged PEC particles as LbL assembly components is a speedy and convenient method to fabricate free-standing LbL multilayer films either with or without nanofillers.