Multilayer films: Assembly and disassembly at different pH conditions
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The objective of this work was to examine the growth and disassembly under different pH conditions of multilayer films composed of polyelectrolytes and a synthetic clay. Multilayer films containing the strong polyelectrolyte poly(diallyldimethylammonium chloride) (PDDA) as a positive building block, and the strong polyelectrolyte poly(styrene sulfonate) (PSS), or the weak polyelectrolyte poly(acrylic acid) (PAA), and/or the synthetic clay Laponite as negative building blocks were assembled using the Layer-by-Layer (LbL) methodology. Both two-component, as well as three-component systems were considered. Large differences in growth rates were observed for PDDA/PAA systems, as well as for PDDA/Laponite systems under different pH conditions. The addition of Laponite into the PDDA/PAA systems resulted in little change in growth rates and no change in relative order compared to the PDDA/PAA two-component system. The addition of PSS to the PDDA/Laponite systems resulted in both changes in growth rates as well as changes in relative order compared to the two-component PDDA/Laponite systems. Multilayer films of PDDA/PAA exhibited significant variation in their disassembly behavior when exposed to different pH conditions. Films were found to be most stable when immersed in aqueous solutions at the same conditions as they were deposited at. Films were slightly less stable when immersed in solutions of a higher pH than they were deposited at. Films were prone to delamination when immersed in solutions at pH 2.