We demonstrate the time- and concentration-dependent dissolution (etching) of polyelectrolyte
multilayer (PEM) films comprised of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) immersed
in NaCl solutions. PEM thickness decreases to a reproducible unchanging value that depends upon the initial
film thickness and the concentration of NaCl. As opposed to a “top-down” removal of PEM chains from the
film, the dissolution mechanism involves the diffusion and association of chains throughout the PEM that leave
the film in the form of polyelectrolyte complexes (PECs). The PEC phase diagram is invoked to explain the
observations presented in this paper and work by previous researchers. We demonstrate the straightforward
application of PEM salt etching to pattern films where the spatial position and amount of dissolved material are
controlled, resulting in a multicolor reflector and a gradient-thickness film. In addition to providing a more
comprehensive picture of PEM stability, these results may help to advance the technological impact of PEMs in
biology and other fields where the ability to create gradients in film thickness could be advantageous.
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