The Compensation Effect in the Vogel–Tammann–Fulcher (VTF) Equation for Polymer-Based Electrolytes

Single-ion conducting polymer electrolytes have been proposed to significantly enhance lithium ion battery performance by eliminating concentration gradients within the cell. Such electrolytes have universally suffered from poor conductivity at low to moderate temperatures. In an attempt to improve conductivity, numerous studies have sought to better understand the fundamental interplay of ion content and segmental motion, with typical analyses relying on a fit of temperature-dependent conductivity data using the Vogel–Tammann–Fulcher (VTF) equation to assist in separating these effects. In this study, we leverage the large accessible composition window of a newly synthesized, single ion conducting polysulfone–poly­(ethylene glycol) (PSf-<i>co</i>-PEG) miscible random copolymer to more completely understand the interrelationship of glass transition temperature, ion content, and the polymer’s Li⁺ conductivity. It is demonstrated here that choice of fitting procedure and Vogel temperature plays a crucial role in the observed trends, and importantly, after optimization of the data fitting procedure, a strong positive correlation was observed between the VTF equation prefactor and apparent activation energy for polymers in this electrolyte class. This relationship, known as the compensation effect (among other names) for the related Arrhenius-type behavior of activated processes such as chemical kinetics and diffusion, is shown here to exist in several other polymer electrolyte classes. Given conductivity’s inverse exponential dependence on the apparent activation energy, maximum conductivity within an electrolyte class is achieved in samples where the activation energy is small. For a system in which the compensation effect exists, decreasing activation energy also decreases the prefactor, highlighting the limiting nature of the compensation effect and the importance of escaping from it. Blending of small molecules is shown to break the apparent trend within the PSf-<i>co</i>-PEG system, suggesting a clear route to high transference number, high conductivity electrolytes

Enhancing Separation and Mechanical Performance of Hybrid Membranes through Nanoparticle Surface Modification

Membranes with selective gas transport properties and good mechanical integrity are increasingly desired to replace current energy intensive approaches to gas separation. Here, we report on the dual enhancement of transport and mechanical properties of hybrid cross-linked poly­(ethylene glycol) membranes with aminopropyl-modified silica nanoparticles. CO₂ permeability in hybrid membranes exceeds what can be predicted by Maxwell’s equation and surpasses values of the pure polymer. Furthermore, dynamic mechanical and thermogravimetric analyses reveal increases in both the storage modulus and thermal stability in hybrid membranes, with respect to silica nanoparticle loading

Sequence of Hydrophobic and Hydrophilic Residues in Amphiphilic Polymer Coatings Affects Surface Structure and Marine Antifouling/Fouling Release Properties

Amphiphilic polymers, specifically combinations of hydrophilic and hydrophobic residues, have been shown to be effective as antifouling materials against the algae <i>Ulva linza</i> and <i>Navicula</i> diatoms. Here we use the inherent sequence specificity of polypeptoids made by solid-phase synthesis to show that the sequence of hydrophilic (methoxy) and hydrophobic (fluorinated) moieties affects both antifouling and fouling release of <i>U. linza</i>. The platform used to test these sequences was a polystyrene-<i>b</i>-poly­(ethylene oxide-<i>co</i>-allyl glycidyl ether) (PS-<i>b</i>-P­(EO-<i>co</i>-AGE)) scaffold, where the polypeptoids are attached to the scaffold using thiol–ene click chemistry. The fluorinated moiety is very surface active and directs the surface composition of the polymer thin film. The position and number of fluorinated groups in the polypeptoid are shown to affect both the surface composition and antifouling properties of the film. Specifically, the position of the fluorinated units in the peptoid chain changes the surface chemistry and the antifouling behavior, while the number of fluorinated residues affects the fouling-release properties