Comparison of KBr and NaCl effects on the glass transition temperature of hydrated layer-by-layer assemblies

Abstract

The influence of assembly and post-assembly conditions on the glass transition temperature of free-standing poly(diallyldimethyl ammonium) (PDADMA)/poly(4-styrene sulfonate) (PSS) layer-by-layer (LbL) films assembled in 0.5M NaCl and 0.5M KBr are explored using modulated differential scanning calorimetry. Upon completion, PDADMA/PSS LbL assemblies are hydrated using solutions containing various concentrations of KBr. The data indicate that water provides the primary driving force for changes in the glass transition temperature of completed films rather than the post-assembly salt type. However, upon changing the assembly salt conditions from NaCl to KBr, the glass transition temperature shows a decrease of nearly 20 °C. Additionally, the composition of the films upon analysis with 1H NMR spectroscopy and neutron activation analysis indicates an elevated number of extrinsic binding sites within the film structure when KBr is the assembly salt. This shows a clear link between the assembly conditions and the internal structure and, therefore, the thermal properties of PDADMA/PSS LbL assemblies.

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).…”

“…These results were further extended to show that it was possible to perform both a time-temperature and a time-water superposition at constant salt because the variation in the intrinsic ion pair concentration was minimal. 200 Ultimately, these three areas of study into coacervate dynamics consider a wide range of time/length scales; the work on glass transition-like thermal transitions considers local segmental and water dynamics, 194,203,[205][206][207][208][209] while the time-salt superposition work borrows from the 'sticky Rouse' theories that consider the dynamics of the entire chain conformation. 37,57,201 These areas of recent progress thus remain only brief glimpses at a rich dynamic behavior of coacervate dynamics and rheology, and suggest the importance of hydration and other atomistic-level effects in the practical application of these materials.…”

“…This is where there is already some atomistic simulation work, with a focus on polypeptide chirality 188,275 and glassy polyelectrolyte complexes has made progress. 167,200,203,206,207 These studies have elucidated key aspects of these non-equilibrium states, including the central role of water structure in complex dynamics 167,200,203,[205][206][207] and the importance of racemic peptide sequences in the formation of polypeptide coacervates. 188,275 However, these specific dynamic and structural effects represent only initial forays into understanding these complexes; for example, there is no comprehensive understanding of how and why these trapped states occur, nor is there any consensus on the highly process-dependent molecular structure.…”

Temperature Window for Encapsulation of an Enzyme into Thermally Shrunk, CaCO3 Templated Polyelectrolyte Multilayer Capsules

“…Since these polymers have a glass transition temperature at ~ 40°C, determined by differential scanning calorimetry, [29] heating the capsules above this temperature allows reorganisation of polymers accompanied with the size reduction of PEM microcapsules. The glass transition temperature depends on the polyelectrolyte polymers, water molecules, [30,31] complexation of polymers, [32] and salt ions [33] in the solution. Temperature can affect the structure of both as-prepared multilayers and also growing ones (10.1039/c6cp00345a).…”