A Raman spectro-microscopic investigation of ETFE-based radiation-grafted anion-exchange membranes

Abstract

This study used Raman spectro-microscopy to investigate the synthesis and degradation of radiation-grafted anion-exchange membranes (RG-AEM) made using 50 μm thick poly(ethylene-co-tetrafluoroethylene) (ETFE) films, vinylbenzyl chloride (VBC) monomer, and 1-methylpyrrolidine (MPY) amination agent. The data obtained confirmed the operation of the grafting-front mechanism. VBC grafting times of 1 and 4 h led to low degrees of grafting homogeneity, while 72 h led to extreme levels of grafting that resulted in mechanically weak RG-AEMs due to the excessive H2O contents. A grafting time of 16 h was optimal yielding a RG-AEM with an ion-exchange capacity (IEC) of 2.06 ± 0.02 mmol g-1 (n = 3). An excess of grafting was detected at the surface of this RG-AEM (at least within the first few μm of the surface). This RG-AEM was then degraded in O2-purged aqueous KOH (1.0 mol dm-3) for 14 d at 80 °C. Degradation was detected throughout the RG-AEM cross-section, where the Raman data was quantitatively consistent with the loss of IEC. A slight excess of degradation was detected at the surface of the RG-AEM. Degradation involved the loss of whole benzyl-1-methypyrrolidinium grafted units as well as the direct attack on the pendent (cationic) pyrrolidinium groups by the hydroxide anions

The alkali degradation of LDPE-based radiation-grafted anion-exchange membranes studied using different ex situ methods

“…As the relative standard deviation (RSD) was <3%, graing homogeneity was deemed to be very good. 44 IECs of the L-AEMs as synthesized (in Cl À -forms)…”

Aryl ether-free polymer electrolytes for electrochemical and energy devices

“…391 With the radiation-grafting of dense substrates, such as ETFE films, the grafting front mechanism can operate. 385,394 This is where the monomer initially co-polymerizes onto the surface of the film (after low grafting durations), after which the monomer can penetrate further and further into the core of the film (after longer grafting durations), until homogeneous grafting levels are achieved throughout the bulk of the newly formed membrane. If such a mechanism is operating, then this can place an upper limit to the thickness of the films (or diameters of powders/fibres) that can be homogeneously grafted through the bulk; a good rule of thumb range is 100-200 mm maximum film thicknesses, depending on the substrate and grafting conditions.…”

Laser-Based Characterisation of the Copper Uranyl Sulphate, Johannite

“…The same sample mounting method used for luminescence analysis was applied to measure the Raman spectra from a Renishaw InVia Reflex Microscope (inVia TM , Reinshaw plc, Wotton-under-Edge, Gloucestershire, UK) equipped with four lasers operating at 785, 633, 532, and 457 nm with a typical laser power of 1.5, 2.0, 2.5, and 0.1 mW, a grating size of 1200, 1800, 2400, and 2400 nm, and a laser beam spot size of 1.28, 1.03, 0.87, and 0.74 μm, respectively [31]. Each spectrum was measured using a ×50 magnification lens from four accumulations with a laser exposure time of 10 s per accumulation.…”