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 <i>T</i><sub>tr</sub> under 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