Investigation of Multilayer Pervaporation Membrane by Positron Annihilation Spectroscopy

Abstract

To investigate the polyamide thin-film composite membranes structure in regard to the variation in the free volume in thin-film composite membrane polyamide active layers, positron annihilation spectroscopy (PAS) experiments using a slow positron beam were performed. The correlation between the pervaporation performance and polyamide active layer free volume explored using the slow positron beam technique was also investigated. The composite membranes were prepared via the interfacial polymerization reaction between ethylenediamine (EDA) and trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane (EDA−TMC/mPAN). The variations in the S parameter at positron incident energies of 0.5−2.5 keV indicate a decrease in the S parameter when the concentration of EDA in aqueous solution increased from 0.5 to 10 wt %. The positron annihilation took place at the surface of the polyamide active layer for the variations at low S parameters and high W parameters (positron incident energy <0.5 keV). The positron annihilation occurred at the free volume in the polyamide active layer for the variations at high S parameters and low W parameters (positron incident energy: 0.5−2.5 keV). From the o-Ps lifetime results, the density of EDA−TMC polyamide active layer decreases along the thin-film growth direction from the aqueous phase toward the organic phase in the range of 1−2 keV positron incident energy. From the positron annihilation lifetime spectroscopy, the variation in the free volume in the EDA−TMC active layer showed a good correlation with the pervaporation performance.

Characterization and pervaporation dehydration of heat-treatment PAN hollow fiber membranes

“…The S parameter is defined by the ratio of the central part of the annihilation spectrum to the total spectrum reflecting positron annihilation using low-momentum valence electrons. The S parameter value increases with increasing the relative contribution of low momentum electrons to the positron annihilation in the open volume defects [19,[21][22][23][24][25][26]. Therefore, DBES can be performed to measure the variation in free volume of a membrane.…”

“…The positron annihilation spectroscopy (PAS) technique is based on an investigation on annihilation phenomena after injecting positrons into the membrane. Recently, PAS becomes a new important method for probing the variation of free volume in the membranes [19][20][21][22][23][24][25][26]. The positron will be annihilated with an electron and emitted with two 511 keV ␥ quanta when the positron is implanted into a condensed matter.…”

Interfacially polymerized thin-film composite polyamide membrane: positron annihilation spectroscopic study, characterization and pervaporation performance

“…The S parameter value increases by increasing the relative contribution of low momentum electrons to the positron annihilation in the open volume voids. [18][19][24][25] DBES can, therefore, be applied to measure the variation in free volume in a composite membrane. The multilayer structure of a composite membrane can be analyzed from the S parameter variation (free volume variation).…”

“…Studies on interfacially polymerized thin-film composite (TFC) membranes are usually about their application in reverse osmosis [7][8][9][10][11] or nanofiltration, [12][13][14][15][16] but few reports on their application in pervaporation are available. [17][18][19] Therefore, in this study, to improve the pervaporation performance of polyamide membranes, TFC polyamide membranes were prepared through the interfacial polymerization reaction between amines (m-phenylenediamine (MPDA) or 1,3-phenylenediamine-4-sulfonic acid (MPDASA) (sulfonated MPDA)) and acyl chloride (trimesoyl chloride (TMC)) on the surface of a modified asymmetric polyacrylonitrile (mPAN) membrane. These TFC polyamide membranes were then applied in the pervaporation separation of aqueous isopropanol solution at 25 1C The polyamide layer's characteristics such as morphology, surface roughness, hydrophilicity, degree of crosslinking, free volume and thickness were correlated with the pervaporation performance.…”

“…[20][21][22][23] However, there are few studies on polymeric TFC pervaporation membranes investigated with PAS. [18][19][24][25] In this regard, to probe the variation in the free volume in the active polyamide layer, the TFC polyamide membrane was examined by conducting PAS experiments, in which a variable monoenergy slow-positron beam was used.…”