The Effect of Assembly Technique on Weak Polyelectrolyte Multilayer Film Morphology and Humidity Swelling/Deswelling Behavior

Yin, Ziyang M.S.Ch.E Rose-Hulman Institute of Technology February 2016 The Effect of Assembly Technique on Weak Polyelectrolyte Multilayer Film Morphology and Humidity Swelling/Deswelling Behavior Thesis Advisor: Dr. Adam Nolte Summary: The goal of this research is to investigate the film morphology and humidity swelling/deswelling behavior of polyelectrolyte multilayers (PEMs) that are constructed from poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) by two assembly techniques: automated dipping layer-by-layer (LbL) and spin-assisted (SA) LbL. Two sets of pH polyelectrolyte solution conditions were tested: (PAH7.5/PAA3.5) and (PAH7.0/PAA7.0). It was found that when the films were constructed with the same number of bilayers (=20 bilayers), SA-LbL (PAH7.5/PAA3.5) has a greater thickness than (PAH7.0/PAA7.0). (PAH7.5/PAA3.5) thin films constructed by automated dipping LbL did not result in a uniform film morphology, making thickness comparisons between techniques for those assembly conditions difficult. On the other hand, the thickness of (PAH7.0/PAA7.0)20 thin films constructed by automated dipping LbL was a tenth of the thickness of (PAH7.0/PAA7.0)20 thin films constructed by SA-LbL. In addition, film morphology was studied for the uneven automated dipping LbL (PAH7.5/PAA3.5)20 thin film using contact mode AFM. Silane treatment and an adsorbed polyethylenimine (PEI) underlayer were attempted to produce a smooth film surface. However, neither surface treatments gave a smooth film surface for the uneven automated dip-coated LbL (PAH7.5/PAA3.5)20. Therefore, the assembly technique is an important factor on the thin film thickness and film morphology. Humidity swelling/deswelling tests were carried out on SA-LbL (PAH7.5/PAA3.5)20, SA-LbL (PAH7.0/PAA7.0)20, and automated dip-coated LbL (PAH7.0/PAA7.0)20. SALbL (PAH7.5/PAA3.5)20 and SA-LbL (PAH7.0/PAA7.0)20 demonstrated a maximum swelling of approximately 40% under a humid air environment. However, the humidity hysteresis effect for the automated dipping LbL (PAH7.0/PAA7.0)20 was hard to tell due to the high uncertainty in the film thickness. DEDICATION I would like to dedicate this thesis to my wonderful parents who have always supported me with my studies in all means. My parents, Lubing Yin and Lanping Wang, have supported me with their love and care throughout my study journey in the U.S. I would not have gone this far without them. Thanks for your amazing parenting and constant support. I am about to embark a new journey of my life. Thank you very much! ACKNOWLEDGEMENT I would like to thank my thesis advisor Dr. Adam J. Nolte for his assistance and guidance throughout this project. I would like to thank Mr. Frank Cunning, technician from the Chemical Engineering Department for his help with setting up the experimental equipment. I would like to acknowledge support from Rose-Hulman Institute of Technology Office of Graduate Studies. In addition, acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for partial support of this research. Finally, yet importantly, I would like to thank my parents and friends for their encouragement and support along this journey.