Preparation and characterization of polyelectrolyte multilayer films containing in-situ synthesized nanoparticles of Cu(OH)2

Copper ions-loaded polyelectrolyte multilayer films (PEMs) of poly(acrylic acid), coded as PAA, and poly(diallyldimethylammonium chloride), coded as PDDA, were constructed on silicon substrate via layer-by-layer (LBL) self-assembly, using CuCl2 blended in the electrolyte solution as the source of Cu2+. Cu(OH)2 nanoparticles were then in-situ synthesized in the multilayer films by immersion of the copper ions-loaded PEMs into 0.1 M NaOH solution. The Cu2+-loaded PAA/PDDA multilayer films and those doped with in-situ Cu(OH)2 nanoparticles were characterized by means of ultraviolet–visible light (UV–vis) absorption spectrometry, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The friction and wear behaviors of the multilayer films sliding against 440C stainless steel counterparts were evaluated using a UMT-2 multifunctional micro tribometer. Results indicate that the Cu2+-loaded PAA/PDDA multilayers with a bilayer number of 2–8 show similar UV–vis absorbance features, and no noticeable accumulation in the amount of Cu2+ occurs during the fabrication of the multilayers, possibly owing to a weak bonding between Cu2+ and –COO−. The blue-shift of the absorption peak of –COO−–Cu2+ band, observed for PAA/PDDA multiplayer films, becomes more obvious after being doped with in-situ Cu(OH)2 nanoparticles. The final Cu(OH)2 nanoparticles-doped PAA/PDDA multilayer films have excellent friction-reducing and antiwear abilities, possibly owing to the modification and refining of their morphology and microstructure by the in-situ doped Cu(OH)2 nanoparticles. The present approach could be extended to incorporate nanoparticles of other types of metal ions into the final PEMs to realize multifunctionalization.