Effects of humidity on the thickness and Young's modulus of polyelectrolyte multilayer films

PMSE 116

Adam J. Nolte, ajn@mit.edu1, Neil D. Treat2, Michael F. Rubner, rubner@mit.edu1, and Robert E. Cohen3. (1) Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, (2) School of Polymers and High Performance Materials, The University of Southern Mississippi, 118 College Drive #10076, Hattiesburg, MS 39406, (3) Department of Chemical Engineering, Massachusetts Institute of Technology, MA
Polyelectrolyte multilayers (PEMs) are formed via the layer-by-layer deposition of oppositely charged polymer molecules from aqueous solutions. A number of potential applications have been suggested for these thin, conformable polymer films; many of these applications rely on the response of the PEM to the water activity in the ambient environment. In this work, we present a systematic investigation of the effect of relative humidity (RH) on the thickness and Young's modulus of three different PEM systems. All of the systems that we studied display humidity-induced swelling and plasticization; however, the internal chemistry and molecular architecture of different PEM assemblies, as controlled by the polyelectrolyte types and the pH values at which they are assembled, lead to unique responses of these systems to changes in ambient humidity. The ability to continuously control the humidity at which the films are studied yields information that would not be obtainable by simply studying PEM films in the wet or dry states alone.