A diverse view of science to catalyse change

Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do. We must value diversity not only in words, but also in actions

A diverse view of science to catalyse change:Valuing diversity leads to scientific excellence, the progress of science and, most importantly, it is simply the right thing to do. we must value diversity not only in words, but also in actions

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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

Hydration and Temperature Response of Water Mobility in Poly(diallyldimethylammonium)-Poly(sodium 4-styrenesulfonate) Complexes

The combination of all-atom molecular dynamics simulations with differential scanning calorimetry (DSC) has been exploited to investigate the influence of temperature and hydration on the water distribution and mobility in poly(diallyldimethylammonium) (PDADMA) and poly(sodium 4-styrenesulfonate) (PSS) complexes. The findings show that the vast majority of the water molecules hydrating the polyelectrolyte complexes (PECs) with 18-30 wt % hydration are effectively immobilized due to the strong interactions between the PE charge groups and water. Temperature and hydration were found to decrease similarly the fraction of strongly bound water. Additionally, at low hydration or at low temperatures, water motions become dominantly local vibrations and rotations instead of translational motion; translation dominance is recovered in a similar fashion by increase of both temperature and hydration. DSC experiments corroborate the simulation findings by showing that nonfreezing, bound water dominates in hydrated PECs atcomparable hydrations. Our results raise attention to water as an equal variable to temperature in the design and engineering of stimuli-responsive polyelectrolyte materials and provide mechanistic explanation for the similarity.Peer reviewe

Confinement Effects on Crystallization and Curie Transitions of Poly(vinylidene fluoride-co-trifluoroethylene)

International audienceNanoscale patterning of piezoelectric and ferroelectric polymers, such as polyvinylidene fluoride (PVdF) and its copolymers with trifluoroethylene (PVdF-TrFE), is increasingly important in organic electronics, memory, and sensing. The nanoscale processing of polymers can lead to materials behavior that is strikingly different from the bulk because of confinement effects. Here we report the effects of confinement of PVdF-TrFE melt-wetted in porous templates of varying pore diameter. PVdF-TrFE is particularly interesting because it possesses a solid-state Curie transition, where both ferro and nonferroelectric phases crystallize into a paraelectric phase. Using modulated differential scanning calorimetry (MDSC), X-ray diffraction (XRD), and broadband dielectric spectroscopy (BDS), we demonstrate that confined PVdF-TrFE crystallizes into an oriented ferroelectric beta phase. Both melting and crystallization temperatures decrease with decreasing pore diameter, and the Curie temperature is weakly affected. Results imply that nanoconfinement enhances the formation and orientation of the ferroelectric beta phase and could potentially enhance ferroelectricty and piezoelectricity in nanoscale PVdF-TrFE features

Relaxation times of solid-like polyelectrolyte complexes of varying pH and water content

This work was supported by the National Science Foundation (grant no. 1905732) (J.L.L.), the National Science Centre, Poland (grant no. 2018/31/D/ST5/01866) (P.B.), and the Academy of Finland (project no. 309324) (M.S.). Computational resources by the PLGrid Infrastructure, Poland, CSC IT Centre for Science, Finland, and RAMI—RawMatTERS Finland Infrastructure are also gratefully acknowledged. M.S. is grateful for the support by the FinnCERES Materials Bioeconomy Ecosystem and use of the Bioeconomy Infrastructure at Aalto.The effect of complexation pH and water on the relaxation time and dynamics of polyelectrolyte (PE) complexes (PECs) and coacervates remains poorly understood. Here, we describe the dynamic mechanical behavior of solid-like PECs containing weak PEs poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) at varying complexation pH, relative humidity, and temperature with support from molecular dynamics simulations. Time–temperature, time–water, and time–intrinsic ion pair superposition principles are applied to obtain the relaxation times. It is shown that the natural log of relaxation time in hydrated PAH/PAA PECs is inversely proportional to the volume fraction of water (ln τ ∼ φw–1) for a given complexation pH. For all complexation pH values examined, the natural log of relaxation time collapsed into a single line when plotted against the ratio of the number of intrinsic ion pairs to water molecules (ln (τ) ∼ nintrinsic ion pairs/nwater). Taken together, this suggests that the relaxation of solid-like, hydrated PAH/PAA PECs is mediated by bound water at the intrinsic ion pair.Peer reviewe

Time-Temperature and Time-Water Superposition Principles Applied to Poly(allylamine)/Poly(acrylic acid) Complexes

The dynamic mechanical and rheological behavior of polyelectrolyte coacervates and complex precipitates is of interest for many applications ranging from health to personal care. Hydration is an important factor, but its effect on the dynamic properties of polyelectrolyte complexes (PECs) is poorly understood. Here, we describe the dynamic behavior of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) complex precipitates at varying relative humidity values and temperatures using both dynamic mechanical analysis (DMA) and all-atom molecular dynamics simulations. To mirror the experimental system via simulation, the water content within the PEC is measured and used as the parameter of interest rather than relative humidity. In the experimental DMA, the modulus decreases with both increasing water content and temperature. The data are superimposed into a super master hydrothermal curve using the time-temperature superposition principle and the time-water superposition principle for the first time. The temperature-dependent shift factor (a T ) follows an Arrhenius relation, and the water-dependent shift factor (a W ) follows a log-linear relation with the water content in the complex. These results suggest that both temperature and water affect the dynamics of the PEC by similar mechanisms over the range investigated. All-atom molecular dynamics simulations show that an increase in the water content and temperature leads to similar changes in the polyelectrolyte chain mobility with little effect on the number of intrinsic ion pairs, suggesting the validity of time-water and time-temperature superposition principles.Peer reviewe

Reversibly pH-Responsive Nanoporous Layer-by-Layer Microtubes

Nanoporous layer-by-layer (LbL) microtubes consisting of poly­(allylamine hydrochloride) (PAH) and poly­(acrylic acid) (PAA) are prepared by LbL deposition in porous templates followed by postassembly acid treatment. The formation of the nanoporous structure is studied as a function of solution pH, treatment time, and number of layers. Pore formation is most effective at pH 1.8, requiring only 5 min to achieve a complete transition, and is shown to be reversible. Whereas the inner surface of the porous microtubes is rough, the outer surface is smoother and exhibited isolated pores, suggestive of an asymmetric porous structure