End group cross-linked 2-(dimethylamino) ethylmethacrylate based anion exchange membrane for electrodialysis

Silica Containing Composite Anion Exchange Membranes by Sol-Gel Synthesis: A Short Review

This short review summarizes the literature on composite anion exchange membranes (AEM) containing an organo-silica network formed by sol–gel chemistry. The article covers AEM for diffusion dialysis (DD), for electrochemical energy technologies including fuel cells and redox flow batteries, and for electrodialysis. By applying a vast variety of organically modified silica compounds (ORMOSIL), many composite AEM reported in the last 15 years are based on poly (vinylalcohol) (PVA) or poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) used as polymer matrix. The most stringent requirements are high permselectivity and water flux for DD membranes, while high ionic conductivity is essential for electrochemical applications. Furthermore, the alkaline stability of AEM for fuel cell applications remains a challenging problem that is not yet solved. Possible future topics of investigation on composite AEM containing an organo-silica network are also discussed.

Synthesis and characterization of thermo/pH-sensitive pectin-graft-poly(dimethylaminoethyl methacrylate) coated magnetic nanoparticles

Herein, thermo- and pH-sensitive pectin-graft-poly(dimethylaminoethyl methacrylate) copolymer-coated magnetic nanoparticles were synthesized via a green and rapid synthetic approach based on microwave irradiation. Firstly, a novel thermo- and pH-sensitive pectin-graft-poly(dimethylaminoethyl methacrylate) copolymer (Pec-g-PolyDMAEMA) was synthesized and then, Pec-g-PolyDMAEMA based magnetic nanoparticles (Pec-g-PolyDMAEMA@Fe₃O₄) were produced via microwave-assisted co-precipitation method. The thermo/pH/magnetic field multi-sensitive hybrid nanoparticle was characterized by techniques like TEM, VSM, FT-IR, and TGA/DSC. In vitro release studies of 5-Fluorouracil (FL) were carried out by altering the temperature (37 and 44°C), pH (5.5 and 7.4) and presence of an AMF. The FL release of Pec-g-PolyDMAEMA@Fe₃O₄@FL exhibited pH-sensitive behavior. They showed thermo/pH-sensitive FL release features with the greatest release of FL at 37°C (56%) than at 44°C (40%) and at pH of 7.4 (63%) than at pH of 5.5 (45%) within 48h. The FL release was also significantly increased (100%) with the presence of a 50 mT magnetic field. These results indicate that the developed Pec-g-PolyDMAEMA@Fe₃O₄ nanoparticles are promising in the application of multi-stimuli-sensitive delivery of drugs.

3D Printing of Micropatterned Anion Exchange Membranes

Micropatterned anion exchange membranes (AEMs) have been 3D printed via a photoinitiated free radical polymerization and quaternization process. The photocurable formulation, consisting of diurethane dimethacrylate (DUDA), poly(ethylene glycol) diacrylate (PEGDA), dipentaerythritol penta-/hexa- acrylate, and 4-vinylbenzyl chloride (VBC), was directly cured into patterned films using a custom 3D photolithographic printing process similar to stereolithography. Measurements of water uptake, permselectivity, and ionic resistance were conducted on the quaternized poly(DUDA-co-PEGDA-co-VBC) sample series to determine their suitability as ion exchange membranes. The water uptake of the polymers increased as the ion exchange capacity (IEC) increased due to greater quaternized VBC content. Samples with IEC values between 0.98 to 1.63 mequiv/g were synthesized by varying the VBC content from 15 to 25 wt %. The water uptake was sensitive to the PEGDA content in the network resulting in water uptake values ranging from 85 to 410 wt % by varying the PEGDA fractions from 0 to 60 wt %. The permselectivity of the AEM samples decreased from 0.91 (168 wt %, 1.63 mequiv/g) to 0.85 (410 wt %, 1.63 mequiv/g) with increasing water uptake and to 0.88 (162 wt %, 0.98 mequiv/g) with decreasing IEC. Permselectivity results were relatively consistent with the general understanding of the correlation between permselectivity, water uptake, and ion content of the membrane. Lastly, it was revealed that the ionic resistance of patterned membranes was lower than that of flat membranes with the same material volume or equivalent thickness. A parallel resistance model was used to explain the influence of patterning on the overall measured ionic resistance. This model may provide a way to maximize ion exchange membrane performance by optimizing surface patterns without chemical modification to the membrane.

Alkyl bisimidazolium-mediated crosslinked comb-shaped polymers as highly conductive and stable anion exchange membranes

Crosslinked poly(arylene ether sulfone)s (PES) with pendant alkyl bisimidazolium units, which act as both crosslinkage sites and hydroxide conductors, were developed as anion exchange membranes (AEMs).

Polyacryloyl hydrazide: an efficient, simple, and cost effective precursor to a range of functional materials through hydrazide based click reactions

Preparation and studies of ion exchangeable epoxy resins, stimuli responsive hydrogels, and polymer-dye conjugates have been accomplished through hydrazide based click reactions using polyacryloyl hydrazide (PAH) as the precursor. A convenient synthesis of PAH with quantitative functionality was achieved by treatment of polymethyl acrylate with hydrazine hydrate in the presence of tetra-n-butyl ammonium bromide. PAH was cured with bisphenol A diglycidyl ether (BADGE) at 60 °C to form transparent resins with superior mechanical properties (tensile strength = 2-40 MPa, Young's modulus = 3.3-1043 MPa, and ultimate elongation = 9-75%) compared to the conventional resins prepared using triethylene tetramine. The resins exhibited higher ion exchange capacities (1.2-6.3 mmol/g) compared to the commercial AHA ammonium-type (Tokuyama Co., Japan) membranes. An azo dye with aldehyde functionality was covalently attached to PAH through hydrazone linkage, and the dye labeled PAH exhibited colorimetric sensing ability for base and acids up to micromolar concentration. The swelling of the PAH based hydrogel varied in the range 4-450% depending on the pH and temperature of the medium. The hydrogels gradually released 30% of the original encapsulated dye in a period of 200 h. PAH-hydroxy naphthaldehyde conjugate released 75% of the original loading in ∼11 days at 37 °C and pH 5.0 through cleavage of the -CONHN═C- linkage. The study depicts the versatility of PAH as a precursor and inspires synthesis of a range of new materials based on PAH in the future.

Ionic resistance and permselectivity tradeoffs in anion exchange membranes

Salinity gradient energy technologies, such as reverse electrodialysis (RED) and capacitive mixing based on Donnan potential (Capmix CDP), could help address the global need for noncarbon-based energy. Anion exchange membranes (AEMs) are a key component in these systems, and improved AEMs are needed in order to optimize and extend salinity gradient energy technologies. We measured ionic resistance and permselectivity properties of quaternary ammonium-functionalized AEMs based on poly(sulfone) and poly(phenylene oxide) polymer backbones and developed structure-property relationships between the transport properties and the water content and fixed charge concentration of the membranes. Ion transport and ion exclusion properties depend on the volume fraction of water in the polymer membrane, and the chemical nature of the polymer itself can influence fine-tuning of the transport properties to obtain membranes with other useful properties, such as chemical and dimensional stability. The ionic resistance of the AEMs considered in this study decreased by more than 3 orders of magnitude (i.e., from 3900 to 1.6 Ω m) and the permselectivity decreased by 6% (i.e., from 0.91 to 0.85) as the volume fraction of water in the polymer was varied by a factor of 3.8 (i.e., from 0.1 to 0.38). Water content was used to rationalize a tradeoff relationship between the permselectivity and ionic resistance of these AEMs whereby polymers with higher water content tend to have lower ionic resistance and lower permselectivity. The correlation of ion transport properties with water volume fraction and fixed charge concentration is discussed with emphasis on the importance of considering water volume fraction when interpreting ion transport data.