Thermal Transitions in Polyelectrolyte Assemblies Occur via a Dehydration Mechanism

Abstract

Hydrated polyelectrolyte (PE) complexes and multilayers undergo a well-defined thermal transition that bears resemblance to a glass transition. By combining molecular simulations and differential scanning calorimetry (DSC) of poly(diallyldimethylammonium) (PDAC) and poly(styrenesulfonate) (PSS) multilayers, we establish for the first time that dehydration drives the thermally induced change in plasticization of the complex and in the diffusion behavior of its components. DSC experiments show that the thermal transition appears when the assemblies are hydrated in water, but not in the presence of alcohols, which supports that water is required for this transition. These findings connect PE complexes more generally to thermoresponsive polymers and liquid crystal phases, which bear phase transitions driven by the (de)hydration of functional groups, thus forming a fundamental link toward an integrated understanding of the thermal response of molecular materials in aqueous environments.

Thermal transitions in and structures of dried polyelectrolytes and polyelectrolyte complexes

“…The lack of measured glass transition in the second heating cycle is consistent with the PSS‐water interaction reported by Yildirim et al that results in a lower critical solution temperature‐like transition thermal transition in the range of 70–75 °C . This thermal transition is related to water's transition from a hydrogen bonder to a plasticizer, resulting in more mobile water above 70–75 °C.…”

Recent progress in the science of complex coacervation

“…194,204 Most of the discussion surrounding the idea of intrinsic ion pairing and material properties of polyelectrolyte complexes has been focused on understanding the presence of a glass transitionlike thermal transition. 194,203,[205][206][207][208][209] Lutkenhaus and coworkers explored this effect using kinetically trapped polyelectrolyte complex solids and multilayers where the water and ion content of the material could be varied independently to explore the effect of these parameters on the resulting material properties. Experimental results from differential scanning calorime- The number of water molecules was taken as the total amount water added to the complex.…”

“…try (DSC), thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS), and dynamic mechanical testing (DMA) were compared by molecular dynamics (MD) simulations by Sammelkorpi and coworkers. 63,200,[203][204][205][206][207][208][209][210] These reports ultimately determined that the temperature of the thermal transition between samples prepared at different water, salt, pH, solvent, and other additive contents could be collapsed onto a universal curve by normalizing based on the water concentration per intrinsic ion pair (Figure 12d). 203,206 Furthermore, it was possible to linearize this universal curve by plotting the natural log of the ratio of (water/intrinsic ion pair) as a function of (1/T tr ) (Figure 12e).…”

Thermal Annealing of Polyelectrolyte Multilayers: An Effective Approach for the Enhancement of Cell Adhesion

“…[7] Proteins adsorbed on nonpolar hydrophobic surfaces created by functionalizing self-assembled monolayers with nonpolar groups such as CH 3 or CF 3 in a relatively high concentration led to a large inter-protein and protein-surface interactions, impeding the proper conformation of proteins to interact with cells. [44] It is worth mentioning that the interface tension of the film, which is in contact with the atmosphere during the annealing process, may also act as a driving force for PEM restructuring. Accordingly, cells appear to adhere better on intermediate hydrophilic/ hydrophobic surfaces.…”

“…In fact, it has been recently demonstrated that dehydration drives the thermal induced change in the plasticity of polyelectrolyte complexes and in the diffusion behavior of the polymers involved in the complex formation. [44] It is worth mentioning that the interface tension of the film, which is in contact with the atmosphere during the annealing process, may also act as a driving force for PEM restructuring. [32]…”