Date of Award
Master of Chemical Engineering (MChE)
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.
Yin, Ziyang, "The Effect of Assembly Technique on Weak Polyelectrolyte Multilayer Film Morphology and Humidity Swelling/Deswelling Behavior" (2016). Graduate Theses - Chemical Engineering. 2.