Increasing the ion exchange capacity (IEC, mmol• g −1 ) of anion exchange membranes (AEMs) decreases the dependence of ionic conductivity (σ) and ion pair hydration on limiting conditions of temperature and humidity. We present novel, hydroxide-stable polycationic ionenes having penta-substituted imidazolium repeating units. Variation of N,N′-dialkyl substituents having 1−4 carbons yields a range in IEC (Cl) (1.56− 2.32 mmol•g −1 ). The trend of σ (Cl) ∼ IEC is in agreement with comparable poly(arylimidazolium)s. This is the first report crosscorrelating water uptake (WU) and ionic conductivity of a homologous series of poly(arylimidazolium) ionenes. The AEMs of higher IEC have a lower range in σ and hydration number (λ = WU / IEC) within limits of temperature and humidity. Decreasing IEC correlates to increasing effective activation energy of ion transport (E a(eff.) ), at constant hydration. The AEM of N,N′-dimethyl-2,4,5-arylimidazolium repeating units and the highest IEC provides σ (Cl) = 12 mS•cm −1 (80 °C, 95 RH%) and σ (OH) = 120 mS•cm −1 (40 °C, 90 RH%).

Enhanced chemical and mechanical stability of ultra-thin Aemion+® over first generation Aemion® in anion exchange membrane fuel cells.

In this work, the first AB-type primary-chain poly-(arylimidazole) (AB-PAI) homopolymers were synthesized by Debus-Radziszewski polycondensation. Control of the number-average molecular mass (M̅ n ) by ab initio stoichiometry of a monofunctional end-cap provides the first corroborating evidence for this polycondensation proceeding by Carothers' Step-Growth mechanism. Quaternization of imidazole units in AB-PAI yields statistical poly(arylimidazolium) (AB-PAIm) ionenes. Steric protection of the electrophilic imidazolium C2 is encoded in the AB-type monomer.Exceptionally harsh alkaline conditions are required to quantify degradation of the sterically protected AB-PAIm derivative (in 40 wt % NaOD at 80 °C, 20% loss of imidazolium units is observed by NMR after 72 h). All the AB-PAI and the AB-PAIm are thermally stable up to 250 °C in air. The sterically encumbered, polycationic poly(2-[2,6-dimethylphenyl]-1,3-dimethyl-5-phenylimidazolium) hydroxide (IEC (OH) = 2.08 mmol g −1 ) is a transparent red glass that can be solvated by polar organic solvents and is insoluble in water and aqueous alkali metal hydroxides.

Abstract:The present work describes the acid-triggered condensation of silicic acid, Si(OH) 4 , as directed by selected polycations in aqueous solution in the pH range of 6.5-8.0 at room temperature, without the use of additional solvents or surfactants. This process results in the formation of silica-polyelectrolyte (S-PE) nanocomposites in the form of precipitate or water-dispersible particles. The mean hydrodynamic diameter (d h ) of size distributions of the prepared water-dispersible S-PE composites is presented as a function of the solution pH at which the composite formation was achieved. Poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and block copolymers of DMAEMA and oligo(ethylene glycol) methyl ether methacrylate (OEGMA) were used as weak polyelectrolytes in S-PE composite formation. The activity of the strong polyelectrolytes poly(methacryloxyethyl trimethylammonium iodide) (PMOTAI) and PMOTAI-b-POEGMA in S-PE formation is also examined. The effect of polyelectrolyte strength and the OEGMA block on the formation of the S-PE composites is assessed with respect to the S-PE composites prepared using the PDMAEMA homopolymer. In the presence of the PDMAEMA 60 homopolymer (M w = 9400 g/mol), the size of the dispersible S-PE composites increases with solution pH in the range pH 6.6-8.1, from d h = 30 nm to d h = 800 nm. S-PDMAEMA 60 prepared at pH 7.8 contained 66% silica by mass (TGA). The increase in dispersible S-PE particle size is diminished when directed by PDMAEMA 300 (M w = 47,000 g/mol), reaching a maximum of d h = 75 nm. S-PE composites formed using PDMAEMA-b-POEGMA remain in the range d h = 20-30 nm across this same pH regime. Precipitated S-PE composites were obtained as spheres of up to 200 nm in diameter (SEM) and up to 65% mass content of silica (TGA). The conditions of pH for the preparation of dispersible and precipitate S-PE nanocomposites, as directed by the five selected polyelectrolytes PDMAEMA 60 , PDMAEMA 300 , PMOTAI 60 , PDMAEMA 60 -b-POEGMA 38 and PMOTAI 60 -b-POEGMA 38 is summarized.

We have used Raman spectroscopy with 3 different laser excitation wavelengths (near infrared: 785 nm, green 514 nm, and ultraviolet 325 nm) to study diamond particles as a function of particle size, ranging from 5 nm to 100's of µm. We find that the position of the 1332 cm -1 diamond line varies with particle size as a direct result of heating by the laser. This effect is more significant for lower wavelengths, probably as a result of the increased absorbance by nanodiamond particles in the UV.