Studies of polymer solvation by dielectric relaxation spectroscopy II: Polyethylene glycol in methyl pyrrolidone

Frequency domain dielectric spectroscopy (30 MHz to 72 GHz) is utilized to study solvation in polyethylene glycol (PEG) — methyl pyrrolidone (MPy) mixtures over the whole mixture range at 20 °C, in particular with PEG 200. Further pure PEGs (200 to 400) and butyl glycol (in the pure state and in benzene and n-hexane solution) are considered for comparison to facilitate the assessment of PEG relaxational behavior. It turns out that the PEG-MPy mixtures can be described in terms of a simple solvation model which takes into account only the bulk and the solvating solvent state. The solvation number per repeat unit is about 0.85 in the dilute solution limit. It decreases gradually with increasing PEG concentration in accordance with a solvation equilibrium model.     

Ionic liquid silver salt complexes for propene/propane separation

Properties of the room-temperature liquid complex salt [Ag(propene)(x)][Tf(2)N] have been studied to probe its suitability for acting as active separation layer in immobilised liquid membrane (ILM) concepts for propane/propene separation. The pressure/temperature range of complex formation has been determined and the thermal properties of Ag[Tf(2)N] and [Ag(propene)(x)][Tf(2)N] have been studied by DSC (differential scanning calorimetry) and TGA (thermogravimetric analysis) measurements. Pressure dependent measurements of solubility and diffusivity showed that the observed membrane selectivity is dominated by the solubility selectivity. The self-diffusion coefficient of propene is always smaller compared to propane as propene is temporarily bound to the silver ion in the [Ag(propene)(x)][Tf(2)N] ionic liquid.     

Recognition of phospho sugars and nucleotides with an array of boronic acid appended bipyridinium salts

The solution-phase sensor array of three cationic bis-boronic acid appended benzyl viologens (BBV) and the anionic fluorescent dye, 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS), is able to discriminate among five phospho sugars, four nucleotides and three neutral saccharides in aqueous buffered solution at low mM concentrations. Linear discriminant analysis, principal component analysis, and hierachical cluster analysis studies showed the “discrimination limit” (lowest analyte concentration where the discrimination is still 100%) to be 4 mM. Calculated K_b and F_max/F₀ values from binding curves of the three BBVs with 1-12 were also used to perform multi-variate analyses with very good discrimination results.     

Dimensionally stable Nafion–polyethylene composite membranes for direct methanol fuel cell applications

Nafion^® impregnated Solupor^®, microporous UHMWPE film, (N-PE), Nafion^®117 (N117) and a membrane prepared using a DE2020 Nafion^® dispersion (DE2020) were characterized with respect to their swelling degree (SD), methanol cross-over, proton conductivity and DMFC performance at various methanol concentrations in order to understand the effect of impregnation of an ion-conductive polymer membrane to the fuel cell performance.     

Preparation and characterization of nanofiltration membranes by coating polyethersulfone hollow fibers with sulfonated poly(ether ether ketone) (SPEEK)

A new type of nanofiltration membrane is reported based on coating a sulfonated poly(ether ether ketone) (SPEEK) layer on top of a polyethersulfone support. The membranes were characterized by dextran mixtures, salt solutions as well as negatively charged dyes. The SPEEK coated nanofiltration membranes showed molecular weight cutoff for dextran in the range of ultrafiltration, however, rather high rejection for sodium sulfate; retention for salts in the order of RNa₂SO₄>RNaCl>RMgCl₂$R_{\text{N}{\text{a}}_2\text{S}{\text{O}}_4}>R_{\text{NaCl}}>R_{\text{MgC}{\text{l}}_2}$; in addition, the membranes showed a 97–100% retention to the organic dyes. The rejection rates were improved by an increase in the coating thickness and the polymer concentration in the coating solution at the penalty of permeability decrease. Furthermore, it was found that pore penetration of SPEEK into the support membrane effectively constrained the swelling rate of SPEEK and increased the retention. The Donnan–Steric Pore Model was used to describe the transport properties of the membrane. Modeling identified a very tortuous passage within the active separation layer.     

Transport limitations in ion exchange membranes at low salt concentrations

In this work we show that the electrical resistance of ion exchange membranes strongly depends on the solution concentration: especially at low solution concentrations (<0.1 M NaCl) we observe a very strong increase in electrical resistance of the membrane with decreasing concentration. To understand and clarify this behavior we systematically investigate the influence of the solution concentration on ion transport phenomena in two anion exchange membranes (Neosepta AMX and Fumasep FAD) and two cation exchange membranes (Neosepta CMX and Fumasep FKD) in the concentration range from 0.017 M to 0.5 M NaCl and for different hydrodynamic conditions. The results are highly valuable for processes that operate in the low concentration range (<0.5 M) such as reverse electrodialysis, electrodialysis, microbial fuel cells and capacitive deionization, where the standard membrane characterization values as usually determined in 0.5 M NaCl solutions do not represent the practical application.