Myotis bechsteinii, Bechsteins fladdermus

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

Electrochemical Energy Storage in Poly(dithieno[3,2-b:2′,3′-d]pyrrole) Bearing Pendant Nitroxide Radicals

The design and electrochemical synthesis of a conjugated radical polymer (CRP), poly­(dithieno­[3,2-b:2′,3′-d]­pyrrole) bearing pendant nitroxide radicals, is reported. Conjugated radical polymers potentially offer simultaneous conductivity and redox activity in the context of organic energy storage. One challenge is understanding the internal electron transfer that occurs in CRPs, which affects the electrochemical energy storage properties. The CRP here is purposefully designed to examine the case of when the conjugated backbone’s redox potential is less than that of the organic radical group. Cyclic voltammetry on the as-prepared CRP exhibits two well-resolved redox peaks at <i>E</i>_pa1 = 3.15 V and <i>E</i>_pa2 = 3.61 V vs Li/Li⁺, corresponding to the redox activities of the (dithieno­[3,2-b:2′,3′-d]­pyrrole) (DTP) backbone and nitroxide radical, respectively. Galvanostatic charge/discharge studies also reveal a two-step charge/discharge process. The lower oxidation potential of DTP contributes to a conductive pathway during the charge/discharge process. An internal electron transfer process occurs during the decay of the open circuit potential, as the final potential stabilizes around 3 V. This strategy emphasizes the effects on energy storage when the redox active polymer contains two moieties that are redox active at different potentials, thus impacting future CRP design

Electropolymerized Polythiophenes Bearing Pendant Nitroxide Radicals

We report a facile way to synthesize polythiophenes carrying pendant 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) radicals, here called PTATs, by electropolymerization in boron trifluoride diethyl etherate (BFEE). The spacing between the TEMPO radical and the polythiophene backbone is varied by an alkyl spacer (<i>n</i> = 2, 4, 6), and the electronic and electrochemical properties are examined using UV–vis spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Film morphologies are also studied via scanning electron microscopy (SEM) and atomic force microscopy (AFM), which show that the longer octyl chain placed between thiophene and TEMPO effectively suppresses aggregation. The highest conductivity and electroactivity are observed for <i>n</i> = 4 and <i>n</i> = 6, respectively. Such morphology differences provide an opportunity to better understand the charge transport and energy storage properties in electronic materials

Role of Salt and Water in the Plasticization of PDAC/PSS Polyelectrolyte Assemblies

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>_tr 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

Molecular Origin of the Glass Transition in Polyelectrolyte Assemblies

Water plays a central role in the assembly and the dynamics of charged systems such as proteins, enzymes, DNA, and surfactants. Yet it remains a challenge to resolve how water affects relaxation at a molecular level, particularly for assemblies of oppositely charged macromolecules. Here, the molecular origin of water’s influence on the glass transition is quantified for several charged macromolecular systems. It is revealed that the glass transition temperature (<i>T</i>_g) is controlled by the number of water molecules surrounding an oppositely charged polyelectrolyte–polyelectrolyte intrinsic ion pair as 1/<i>T</i>_g ∼ ln­(<i>n</i>_H₂O/<i>n</i>_{intrinsic ion pair}). This relationship is found to be “general”, as it holds for two completely different types of charged systems (pH- and salt-sensitive) and for both polyelectrolyte complexes and polyelectrolyte multilayers, which are made by different paths. This suggests that water facilitates the relaxation of charged assemblies by reducing attractions between oppositely charged intrinsic ion pairs. This finding impacts current interpretations of relaxation dynamics in charged assemblies and points to water’s important contribution at the molecular level