The influence of attaching hydrophobic side groups to a polyelectrolyte, used for deposition of a multilayer oxygen gas barrier thin film, was investigated. Polyethyleneimine (PEI) was labeled with pyrene and deposited in "quadlayers" of PEI, poly(acrylic acid), PEI, and sodium montmorillonite clay using layer-by-layer assembly. Thin films made of three repeating quadlayers using unmodified PEI had much lower density (1.24 g/cm(3)) than pyrene-labeled PEI-based films (1.45 g/cm(3)), which is believed to be the result of greater chain coiling from the increased hydrophobicity of pendant pyrene groups. This increased density in pyrene- labeled PEI layers allowed three quadlayers to match the oxygen transmission rate of a four quadlayer film made with unmodified PEI. This discovery provides an additional tool for tailoring the barrier behavior of clay-based multilayer thin films that could prove useful for a variety of packaging applications. (C) 2014 Wiley Periodicals, Inc.