title: Accelerated Amidization of Branched Poly(ethylenimine)/Poly(acrylic acid) Multilayer Films by Microwave Heating.
abstract: Chemical cross-linking of layer-by-layer assembled films promotes mechanical stability and robustness in a wide variety of environments, which can be a challenge for polyelectrolyte multilayers in saline environments or for multilayers made from weak polyelectrolytes in environments with extreme pHs. Heating branched poly(ethylenimine)/poly(acrylic acid) (BPEI/PAA) multilayers at sufficiently high temperatures drives amidization and dehydration to covalently cross-link the film, but this reaction is rather slow, typically requiring heating for hours for appreciable cross-linking to occur. Here, a more than one order of magnitude increase in the amidization kinetics is realized through microwave heating of BPEI/PAA multilayers on indium tin oxide (ITO)/glass substrates. The cross-linking reaction is tracked using infrared spectroscopic ellipsometry to monitor the development of the cross-linking products. For thick films (∼1500 nm), gradients in cross-link density can be readily identified by infrared ellipsometry. Such gradients in cross-link density are driven by the temperature gradient developed by the localized heating of ITO by microwaves. This significant acceleration of reactions using microwaves to generate a well-defined cross-link network as well as being a simple method for developing graded materials should open new applications for these polymer films and coatings.
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Kehua
authors.initials: K
authors.lastname: Lin
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Yuanqing
authors.initials: Y
authors.lastname: Gu
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Huan
authors.initials: H
authors.lastname: Zhang
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Qiang
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Bryan D
authors.initials: BD
authors.lastname: Vogt
authors.affiliation: Department of Polymer Engineering, University of Akron , Akron, Ohio 44325, United States.
authors.forename: Nicole S
authors.initials: NS
authors.lastname: Zacharia