Plasticizer effects in polyether electrolytes studied by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) has been used to probe the effects on free volume of the addition of either propylene carbonate or tetraglyme to a polyether-based electrolyte. Despite their very different behaviour as observed by NMR and conductivity measurement, the PALS sensitive free volume of the samples changes in a similar way on addition of the two plasticizers. It is concluded that the effect of these plasticizers on conductivity is determined more by their effect on ion-polymer and ion-ion interactions than by their effect on the PALS free volume.

Ftir study of ion-pairing effects in plasticized polymer electrolytes

The effect of plasticizer on the ubiquitous ion-pairing observed in polymer electrolytes has been investigated using FTIR as a probe of the local environment of the triflate ion in sodium and lithium triflate based electrolytes. Plasticizers having a range of properties, such as, propylene carbonate, and dimethyl formamide (DMF), have been investigated in the pure state for comparison with the polymer (a random copolymer of ethylene oxide at propylene oxide (mol ratio 3: 1)). The different plasticizers exhibited strikingly different effects on the triflate ion bands normally observed in polyether salt systems. In particular, the cation associated triflate ion bands at 1288 and 1248 cm⁻¹ and the band at 1272 cm⁻¹ which has variously been assigned to the free ion and also to the strongly aggregated anion, are different. PC produces a rapid disappearance of the “free” ion band in favour of the monodentate ion pair. On the other hand, DMF strongly enhances the band near 1270 cm⁻¹ at salt concentrations higher than 0.7 mol kg⁻¹. These observations are discussed in terms of recent ab initio calculations of the triflate vibrational bands.

Conducting polymer electrochemistry in ionic liquids

Applications of polymers like polypyrrole and polythiophene often require interaction with an electrolyte consisting of solvent and dissolved salt. Ionic Liquids (ILs) are pure saits, fluid at room temperature, that form charged electrolytes. Pure l-Bu-3-Me-Imidazolium PF₆ (BMI PF₆) a hydrophobic IL that has a wide potential window, was used to investigate the electrochemistry ofpolypyrrole. Enhanced electrochemic~l stability of polypyrrole was obtained on repetitive redox cycling with respect to the equivalent propylene carbonate electrolyte with tetrabutylammonium hexaflurophosphate (TBA PF₆) electrolyte.

Dynamic mechanical thermal analysis studies of factors influencing relaxation in polyetherurethane based solid electrolytes

Dynamic mechanical thermal analysis (DMTA) has been used to study the effects of plasticizers on the mobility and homogeneity of a series of solid polymer electrolytes (SPEs). With reference to previously published results on similar systems containing LiClO₄ salts and tetraglyme as plasticizer, the effects of propylene carbonate (PC) on the glass transition temperature (T_g) of the SPE and on the distribution of relaxation times within the sample are discussed; at low plasticizer concentration PC has little effect on T_g as measured by DMTA in comparison with tetraglyme, and at higher plasticizer concentrations PC significantly broadens the mechanical relaxation behaviour indicating a greater degree of dynamical heterogeneity within the sample. A second low temperature relaxation is evident at lower PC contents indicating that some regions of this plasticized SPE are distinctly more mobile than others or perhaps, on this length scale, that some degree of phase separation is present. Activation energies for the mechanical relaxation were also determined as a function of PC concentration and are significantly greater than those determined from conductivity measurements.

Modification of thermoplastic coatings for improved cathodic disbondment performance on a steel substrate : a study on failure mechanisms

The effect of blending two different materials with a medium density polyethylene for use as pipe coatings is presented. The influence of such blending on properties such as cathodic disbondment (CD) and wet adhesion on steel is investigated. The components blended include a functionalised polyethylene (PE) containing the polar functionality, maleic anhydride (MAH) and an amorphous elastomer, ethylene-propylene-diene terpolymer (EPDM). It was found that modification of PE with small amount (2.5–3 wt%) of either blended MAH-g-PE or EPDM resulted in a significant improvement in CD performance and wet adhesion strength. The mode of failure and disbondment mechanism was investigated using energy dispersive X-ray spectroscopy (EDXS) and X-ray photoelectron spectroscopy (XPS). The greater resistance of migration of sodium ions increases with the incorporation of the modifiers, and it is proposed that this results in an increase in CD performance.

Mechanical properties of polyether-plasticiser-salt systems as polymer electrolytes

The mechanical properties of urethane crosslinked poly(ethylene oxide-co-propylene oxide) glyceryl ether-plasticiser (tetraethylene glycol dimethyl ether, or methylformamide)-salt (LiClO₄)-based polymer electrolytes have been studied. It was found that, with increasing concentration of salt, the elastic modulus and tensile strength of the materials unexpectedly decrease. This is interpreted in terms of a predominance of intramolecular coordination of the Li⁺ ions by the polymer.

Volume confinement induced microstructural transitions and property enhancements of supramolecular soft materials

The rheological properties of supramolecular soft functional materials are determined by the networks within the materials. This research reveals for the first time that the volume confinement during the formation of supramolecular soft functional materials will exert a significant impact on the rheological properties of the materials. A class of small molecular organogels formed by the gelation of N-lauroyl-L-glutamic acid din-butylamide (GP-1) in ethylene glycol (EG) and propylene glycol (PG) solutions were adopted as model systems for this study. It follows that within a confined space, the elasticity of the gel can be enhanced more than 15 times compared with those under un-restricted conditions. According to our optical microscopy observations and rheological measurements, this drastic enhancement is caused by the structural transition from a multi-domain network system to a single network system once the average size of the fiber network of a given material reaches the lowest dimension of the system. The understanding acquired from this work will provide a novel strategy to manipulate the network structure of soft materials, and exert a direct impact on the micro-engineering of such supramolecular materials in micro and nano scales.

Real-time observation of fiber network formation in molecular organogel : supersaturation-dependent microstructure and its related rheological property

Low-molecular mass organic gelators self-organizing into three-dimensional fiber networks within organic solvents have attracted much attention in recent years. However, to date, how the microstructure of fiber network is formed in a gelation process and the key factors that govern the topological structure of a gel network remain to be determined. In this work, we address these issues by investigating the in situ formation of the gel networks in the N-lauroyl-l-glutamic acid di-n-butylamide (GP-1)/propylene glycol (PG) system. By using optical microscopy, the time evolution of the gel network microstructure was investigated under various supersaturation conditions. It is found that supersaturation is one of the key factors that govern the topological structure of a gel network. In particular, the creation of the junctions turns out to be supersaturation-dependent. The rheological experiments further revealed the correlation between topological structure and mechanical properties. It suggests that the rheological properties can be effectively modified by tuning the microstructure topology of the gel network. Our results reported here provide new physical insight into the formation kinetics of a molecular gel. Furthermore, this work could be important in constructing and engineering a supramolecular structure for the purpose of applications.

Microengineering of supramolecular soft materials by design of the crystalline fiber networks

Crystalline spherulitic fiber networks are commonly observed in polymeric and supramolecular functional materials. The elasticity of materials with this type of network is low if interactions between the individual spherulites are weak (mutually exclusive). Improving the elasticity of these materials is necessary because of their important applications in many fields. In this work, the engineering of the microstructures and rheological properties of this type of material is carried out. A small molecule organogel formed by the gelation of N-lauroyl-L-glutamic acid di-n-butylamide (GP-1) in propylene glycol (PG) is used as an example. The elasticity of this material is improved by controlling the thermodynamic driving force, the supersaturation of the gelator, and by using a selected copolymer additive to manipulate the primary nucleation of GP-1. Because of the weak interactions between the GP-1 spherulites, with the same fiber mass, the elasticity of GP-1/PG gel is less than half of those of the other two gels formed by GP-1 and 2-hydroxystearlic acid in solvent benzyl benzoate (BB), which are supported by interconnecting spherulitic fiber networks. This work develops a robust approach to the engineering of supramolecular functional materials especially those with mutually exclusive spherulite fiber networks.

Microengineering of soft functional materials by controlling the fiber network formation

The engineering of soft functional materials based on the construction of three-dimensional interconnecting self-organized nanofiber networks is reported. The system under investigation is an organogel formed by N-lauroyl-L-glutamic acid di-n-butylamide (GP-1) in propylene glycol. The engineering of soft functional materials is implemented by controlling primary nucleation kinetics of GP-1, which can be achieved by both reducing thermodynamic driving force and/or introducing a tiny amount of specific copolymers (i.e., poly(methyl methacrylate comethacrylic acid)). The primary nucleation rate of GP-1 is correlated to the number density of GP-1 spherulites, which determines the overall rheological properties of soft functional materials. The results show that the presence of a tiny amount of the polymer (0.01-0.06%) can effectively inhibit the nucleation of GP-1 spherulites, which leads to the formation of integrated fiber networks. It follows that with the additive approach, the viscoelasticity of the soft functional material is significantly enhanced (i.e., more than 1.5 times at 40 °C). A combination of the thermal and additive approach led to an improvement of 3.5 times in the viscosity of the gel.

Control of crystallization in supramolecular soft materials engineering

As one class of the most important supramolecular functional materials, gels formed by low molecular weight gelators (LMWGs) have many important applications. The key important parameters affecting the in-use performance of a gel are determined by the hierarchical fiber network structures. Fiber networks consisting of weakly interacting multiple domains are commonly observed in gels formed by LMWGs. The rheological properties, particularly the elasticity, of a gel with such a fiber network are weak due to the weak interactions between the individual domains. As achieving desirable rheological properties of such a gel is practically relevant, in this work, we demonstrate the engineering of gels with such a type of fiber network by controlling crystallization of the gelator. Two example gels formed by a glutamic acid derivative in a non-ionic surfactant Tween 80 and in propylene glycol were engineered by controlling the thermodynamic driving force for crystallization. For a fixed gelator concentration, the thermodynamic driving force was manipulated by controlling the temperature for fiber crystallization. It was observed that there exists an optimal temperature at which a gel with maximal elasticity can be fabricated. This will hopefully provide guidelines for producing high performance soft materials by engineering their fiber network structures.

Morphology and mechanical properties of nanostructured thermoset/block copolymer blends with carbon nanoparticles

Here we report the effect of multi-walled carbon nanotubes (MWCNTs) and thermally reduced graphene (TRG) on the miscibility, morphology and final properties of nanostructured epoxy resin with an amphiphilic poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer. The addition of nanoparticles did not have any influence on the miscibility of PEO-PPO-PEO copolymer in the resin. However, MWCNTs and TRG reduced the degree of crystallinity of the PEO-rich microphases in the blends above 10 wt.% of copolymer while they did not change the phase morphology at the nanoscale, where PPO spherical domains of 20-30 nm were found in all the samples studied. A synergic effect between the self-assembled nanostructure and the nanoparticles on the toughness of the cured resin was observed. In addition, the nanoparticles minimized the negative effect of the copolymer on the elastic modulus and glass transition temperature in the resin.

Potential hydraulic barrier performance of cyclic organic carbonate modified bentonite complexes against hyper salinity

The effect of adding glycerol carbonate (GC) or propylene carbonate (PC) to sodium (Na)-bentonite on the hydraulic performance of geosynthetic clay liners (GCLs) under hypersaline conditions is examined. Fluid loss (FL), swell index (SI) and solution retention capacity (SRC) measurements were carried out to compare the potential hydraulic performance of these two cyclic organic carbonates (COCs) as bentonite modifiers. A modified FL test enabled quantitative measurement of both the water retention characteristics of untreated and COC modified bentonites as well as calculation of hydraulic conductivity values. Tests under aggressively saline conditions (ionic strength, I ≥ 1 M of NaCl and ≥3 M of CaCl2) showed that at a mass ratio of 1:1 (GC to bentonite), the FL of a GC-Na-bentonite was ≈40–104 mL in NaCl and ≈61–91 mL in CaCl2. This was about 10–20 mL and 70–200 mL, respectively, lower than that of a comparable PC-Na-bentonite (1:1 PC to bentonite) and untreated Na-bentonite. Greater swelling (SI) and greater solution retention capacity (SRC) was observed for the GC treated Na-bentonite compared to untreated Na-bentonite in all salt solutions, and for PC-Na-bentonite at high ionic strength of both NaCl and CaCl2 solutions, demonstrating the superior hydraulic barrier performance of COC-bentonites under severely saline conditions. Experiments conducted in flexible-wall permeameters with I = 3 M CaCl2 showed approximately one order of magnitude lower (∼10−11 m/s vs ∼1.9 × 10−10 m/s) hydraulic conductivity of GC treated bentonite cake compared to the k value of the untreated Na-bentonite cake. Calculated hydraulic conductivity from fluid loss tests estimated the measured values in a conservative way (overestimation).

Investigating non-fluorinated anions for sodium battery electrolytes based on ionic liquids

In order for sodium batteries to become a safe, lower cost option for large scale energy storage, minimising the price of all components is important. We report here on the application of a pyrrolidinium room temperature ionic liquid comprising the dicyanamide anion as a successful electrolyte system for sodium metal batteries that does not contain expensive fluorinated species. The effects of plating/stripping of sodium from Na metal electrodes has been investigated in a symmetrical Na | electrolyte | Na configuration at a current density of 10 μA cm− 2. Comparisons are drawn to reference organic electrolytes comprising propylene carbonate-fluoroethylene carbonate. Residual water molecules in the ionic liquid electrolyte are observed to have a significant effect upon the surface film and subsequent favourable plating/stripping behaviour of symmetrical cells and this is explored in detail. An increase of the moisture content from 90 ppm to 400 ppm impedes both electrodeposition and electrodissolution of the Na+/Na. This is investigated at Ni electrodes using cyclic voltammetry at different Na+-salt concentrations to further understand the mechanism.