title: Role of Salt and Water in the Plasticization of PDAC/PSS Polyelectrolyte Assemblies.
abstract: In this work, we investigate the effect of salt and water on plasticization and thermal properties of hydrated poly(diallyldimethylammonium chloride) (PDAC) and poly(sodium 4-styrenesulfonate) (PSS) assemblies via molecular dynamics simulations and modulated differential scanning calorimetry (MDSC). Commonly, both water and salt are considered to be plasticizers of hydrated polyelectrolyte assemblies. However, the simulation results presented here show that while water has a plasticizing effect, salt can also have an opposite effect on the PE assemblies. On one hand, the presence of salt ions provides additional free volume for chain motion and weakens PDAC-PSS ion pairing due to electrostatic screening, which contributes toward plasticization of the complex. On the other hand, salt ions bind water in their hydration shells, which decreases water mobility and reduces the plasticization by hydration. Our MDSC results connect the findings to macroscopic PE plasticization and the glass-transition-like thermal transition Ttrunder controlled PE hydration and salt content. This work identifies and characterizes the dual nature of salt both as plasticizer and hardener of PE assemblies and maps the interconnection of the influence of salt with the degree of hydration in the system. Our findings provide insight into the existing literature data, bear fundamental significance in understanding of hydrated polyelectrolyte assemblies, and suggest a direct means to tailor the mechanical characteristics of PE assemblies via interplay of water and salt.
authors.affiliation: State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences , Changchun 130022, P. R. China.
authors.forename: Ran
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Yanpu
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Department of Chemistry, School of Chemical Technology, Aalto University , P.O. Box 16100, FI-00076 Aalto, Finland.
authors.forename: Hanne S
authors.initials: HS
authors.lastname: Antila
authors.affiliation: Artie McFerrin Department of Chemical Engineering, Texas A&M University , College Station, Texas 77843, United States.|Department of Materials Science and Engineering, Texas A&M University , College Station, Texas 77843, United States.
authors.forename: Jodie L
authors.identifier: 0000-0002-2613-6016
authors.initials: JL
authors.lastname: Lutkenhaus
authors.affiliation: Department of Chemistry, School of Chemical Technology, Aalto University , P.O. Box 16100, FI-00076 Aalto, Finland.
authors.forename: Maria
authors.identifier: 0000-0002-9248-430X
authors.initials: M
authors.lastname: Sammalkorpi