Correlating the compliance and permeability of photocrosslinked polyelectrolyte multilayers

• Published in: Langmuir 2011-03, Vol.27 (8), p.4756-4763
• Main Authors: Lehaf, Ali M., Moussallem, Maroun D., Schlenoff, Joseph B.
• Format: Article
• Language: English
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/la200229h

Photocrosslinkable polyelectrolyte multilayers were made from poly(allylamine), PAH and poly(acrylic acid), PAA, modified with a photosensitive benzophenone. Nanoindentation, using atomic force microscopy, AFM, of these and unmodified PAH/PAA multilayers was used to assess their mechanical properties in situ under aqueous buffer. Under the conditions employed (and a 20 nm AFM radius tip) reliable nanoindentations that appeared to be decoupled from the properties of the silicon substrate were obtained for films greater than 150 nm in thickness. A strong difference in apparent modulus was observed for films terminated with positive as compared to negative polyelectrolyte. Films terminated with PAA were more glassy, suggesting better charge matching of polyelectrolytes. Multilayers irradiated up to 100 minutes showed a smooth and controlled increase in modulus, with little change in water contact angle. The permeability to iodide ion, measured electrochemically, also decreased in a controlled fashion