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Interfacial polymerization (IP) is considered as an emerging technique for fabricating pervaporation (PV) membranes. Typically, PV membranes fabricated through IP achieve high separation efficiency and overall performance as they possess characteristics that play vital roles in defying the limiting trade-off between permeation flux and separation factor. There is a great deal of flexibility in the IP technique. Therefore, this article reviews evolving trends in developing PV membranes fabricated through IP in terms of methods of fabrication and modification strategies, active layer and membrane support selections, and potential industrial applications. Moreover, we also emphasized the free volume analysis of the membranes prepared through IP. Future plans for furthering IP as a fabrication technique for PV membranes are also explored.

• Promoting the separation efficiency of pervaporation membranes is a must to meet the growing demands of society. In this study, acetone-assisted interfacial polymerization was employed to produce thin-film composite (TFC) pervaporation membranes with improved performance. Two monomers were considered—diethylenetriamine (DETA) and trimesoyl chloride (TMC); they reacted with each other to form a thin polyamide layer, which was deposited on a hydrolyzed polyacrylonitrile (HPAN) substrate. Aqueous solutions containing different concentrations of acetone were used to dissolve DETA. Introducing acetone as a cosolvent of water enhanced the sorption of DETA in the HPAN support. It also altered and improved the physicochemical properties of the TFC membranes. An optimum concentration of 50 wt% aqueous acetone solution was established. Through acetone-assisted interfacial polymerization, a TFC membrane was then fabricated, and it exhibited a high separation efficiency: permeation flux = 1641 ± 134 g∙m−2 h−1 and water concentration in the permeate = 98%–99% (feed =70 wt% aqueous isopropanol solution). Moreover, the modified TFC membrane displayed a high separation performance at a wide range of operating conditions.

Choosing the property of the supporting membrane is crucial in preparing high performing nanofiltration membranes through interfacial polymerization. In this study, an oxygen rich membrane – cellulose triacetate (CTA) – was used to fabricate the support membrane. Polyamide was deposited onto the CTA support using interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC). The concentration of the monomers was optimized. Furthermore, the polyamide layer prepared on CTA support exhibited higher separation efficiency for sodium sulfates and dyes compared to using traditional polysulfone (PSf) support. The oxygen groups of CTA facilitate better adsorption of amines on the surface; thus, using low concentration of PIP could still provide a defect-free polyamide layer. Utilizing the optimum condition, the polyamide/CTA membrane delivered a high pure water flux (operating at 6 bar) of 179.5 L/m2h with the following rejections: Na2SO4 = 98.4%; MgSO4 = 60.3%; MgCl2 = 15.0%; NaCl = 3.7%; Rose Bengal = 95.5%; Brilliant Blue R = 99.9%; Amido Black 10B = 90.6%; Orange G = 67.3%. Moreover, the polyamide/CTA membrane had excellent stability at a wide range operating conditions.

Graphene quantum dots(GQDs) were used to possibly cover the structural defects on the graphitic regions of reduced graphene oxide(rGO). The resulting homostructure nanocomposite fillers(rGO + GQD) were incorporated in an alginate solution creating a dense composite membrane for pervaporation. The membranes were applied to separate alcohol/water mixtures in which the successful covering of structural defects was observed with good separation performance of lower molecular weight alcohols. The Raman spectra and elemental analyses confirmed the successful changes on the physical and chemical structures of the homostructured fillers. The X-ray diffraction pattern showed that the crystallinity of the membrane was greatly affected when incorporated with rGO + GQD. The alginate incorporated with 3 wt% of rGO + GQD(Alg-rGO + GQD) has the best pervaporation performance in separating methanol/water mixture with a permeation flux of 2323 g m−2 h−1 and water concentration in permeate of 92.7% at 70 °C. While the positron annihilation lifetime spectroscopy results supported that the minimization of the structural defects enhanced the water selectivity of the membrane by easy transport of water molecules through the free volume spaces and blocks methanol molecules. The results in this study may provide the possible sealing or curing the defects on rGO with GQDs and improve the interfacial interaction with the polymer matrix.

We modified thin-film nanofiltration membranes by embedding in them silica nanoparticles (SiNPs) coated with polydopamine (PDA), which is well-known to mimic the adhesive characteristics of mussels. The coating process was triggered by the oxidative self-polymerization of dopamine on the surface of SiNPs, and the membranes were fabricated through interfacial polymerization (reaction between piperazine and trimesoyl chloride, TMC). Thin-film nanofiltration membranes embedded with PDA-SiNPs (TFNPDA-SiNPs) were compared with pristine polyamide membrane, as well as with polyamide membrane embedded with uncoated SiNPs. Energy-dispersive X-ray spectroscopy confirmed that TFNPDA-SiNPs contained more nanoparticles than the polyamide membrane with uncoated SiNPs. Accordingly, the hydrophilicity of TFNPDA-SiNPs was higher. TFNPDA-SiNPs fabricated from using a concentration of 0.35 g PDA-SiNPs/g TMC delivered the highest pure water flux of 80.0 ± 4.6 L⋅m−2⋅h−1 at 6 bar; salt rejections were as follows: RNa2SO4 = 97%; RMgSO4 = 94%; RMgCl2 = 68%; RNaCl = 35%. The TFNPDA-SiNPs also demonstrated the greatest antifouling ability, as its flux was the highest at the end of three cycles of antifouling tests, where bovine serum albumin was used as model protein foulant.

Thin-film nanocomposite (TFN) membranes enjoy advantages over the traditional membranes for water purification purposes. TFN membranes are fabricated primarily through interfacial polymerization: d...

A series of thin-film composite (TFC) polyamide membranes was fabricated through interfacial polymerization on a modified polyacrylonitrile (mPAN) substrate, where an aqueous solution of diamine was reacted with an organic solution of diacyl chloride. Various monomers were used: two different diamines [1,3-diamino-2-propanol (DAPL) and hydrazine] and two different diacyl chlorides [succinyl chloride (SCC) and trans-5-norbornene-2,3-dicarbonyl chloride]. Combining these monomers resulted in a new polyamide layer. We investigated the effect of the monomer chemical structure and interfacial polymerization conditions on the membrane pervaporation performance in dehydrating an aqueous solution of ethanol. According to field emission scanning electron microscopy, DAPL-SCC provided the thinnest polyamide layer, which was also confirmed through positron annihilation lifetime spectroscopy. The results were used to correlate the variation in the membrane microstructure with the pervaporation performance of the fabricated TFC polyamide membranes. Both microstructural characteristics and surface properties affected the pervaporation performance. DAPL-SCC/mPAN membranes with lower free-volume sizes and suitable hydrophilicity were evaluated to deliver the highest water concentration in permeate and the lowest permeation flux (on the basis of the pervaporative dehydration of an aqueous solution of 90 wt% ethanol at 25 °C).

We propose in this study a facile and versatile strategy for fabricating thin-film nanocomposite (TFN) membranes, wherein polydopamine-piperazine (PDP) nanoparticles were formed in situ from the oxidative polymerization reaction of dopamine and its subsequent reaction with piperazine. Accordingly, PDP nanoparticles were then directly used as nanofillers for TFN membranes fabricated through interfacial polymerization. The characteristics of PDP nanoparticles and the performance of TFN membranes were easily tailored by varying the water-ethanol ratio in the PIP solution, solution pH, dopamine concentration, and reaction time. The TFN-PDP membranes exhibited an optimum separation performance (high water permeability and high salt selectivity): JH2O = 59.1 ± 3.3 L m−2 h−1; RNa2SO4 = 98.0%; RNaCl = 44.1% (6 bar, 25 °C). Moreover, the TFN-PDP membranes demonstrated high water flux recovery and enhanced antifouling property during cycles of filtration tests, with bovine serum albumin protein used as model foulant.

We synthesized silica particles with varying sizes of 50, 200, and 500 nm. These particles were added to a trimesoyl chloride (TMC) solution and used as fillers to produce thin-film nanocomposite (TFN) polyamide membranes through interfacial polymerization. The effect of the particle size and concentration on the nanofiltration membrane performance was systematically investigated. Scanning electron microscopic images showed that small particles were dispersed in the membrane with spaces between them, but large particles clustered together and gathered into a crowd or mass, forming a layer of particles. When the particle concentration was low (0.35 g silica/g TMC), TFN50 (membrane with 50-nm particles, the smallest of the additives used in this study) delivered the highest pure water flux (58.3 ± 3.8 L m−2 h−1); the salt rejection [RNa2SO4 (99.0 ± 0.6%) > RMgSO4 (96.5 ± 2.6%) > RMgCl2 (67.2 ± 1.3%) > RNaCl (42.6 ± 2.3%)] was comparable with that for the other membranes. At a high concentration of particles (0.75 g silica/g TMC), the water flux delivered by membranes that differed in the size of embedded particles was the same; however, the salt rejection decreased with increasing particle size. In antifouling tests with bovine serum albumin used as model foulant, membranes with silica particles indicated high water flux recovery and remarkable antifouling property.

The advancement in membrane science and technology, particularly in nanofiltration applications, involves the blending of functional nanocomposites into the membranes to improve the membrane property. In this study, Ag-polydopamine (Ag-PDA) particles were synthesized through in situ PDA-mediated reduction of AgNO3 to silver. Infusing Ag-PDA particles into polyethersulfone (PES) matrix affects the membrane property and performance. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of Ag-PDA particles on the membrane surface. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) describe the morphology of the membranes. At an optimum concentration of Ag-PDA particles (0.3 wt % based on the concentration of PES), the modified membrane exhibited high water flux 13.33 L∙m−2∙h−1 at 4 bar with high rejection for various dyes of &gt, 99%. The PESAg-PDA0.3 membrane had a pure water flux more than 5.4 times higher than that of a pristine membrane. Furthermore, in bacterial attachment using Escherichia coli, the modified membrane displayed less bacterial attachment compared with the pristine membrane. Therefore, immobilizing Ag-PDA particles into the PES matrix enhanced the membrane performance and antibacterial property.

In this study, polydopamine (PDA) particles were embedded into polyethersulfone (PES) membrane through wet-phase separation. We considered two concentration of PES solution—17 and 19 wt%. Adding different concentration of PDA (0–0.7 wt%) into the two solutions revealed an opposite effect on the characteristic and performance of the membrane. Incorporating PDA particles in 17 wt% PES solution was resulted in a decreased in pure water flux, and increased in dye rejection; Whereas, incorporating PDA particles in 19 wt% PES solution boosted the pure water flux with keep dye rejection of ~99.0%. At the optimum concentration of 0.5 wt% PDA added to 19 wt% PES solution, the following dye rejections were obtained: RMethylene Blue = 99.90 ± 1.45%; RProcion Blue H-5R = 98.33 ± 0.57%; RDirect Red 23 = 99.90 ± 1.82%; RBrilliant Blue = 99.90 ± 0.94%; RRose Bengal = 99.90 ± 0.0%; RDirect Red 80 = 99.12 ± 0.41%; for the salt rejections: (RNaCl = 10.59 ± 5.23%; RNa2SO4 = 8.87 ± 4.99%; RMgCl2 = 10.45 ± 6.85%; RMgSO4 = 10.02 ± 3.87%). This shows that the selectivity of the fabricated membrane towards different dyes and common inorganic salts is high. PDA is a favorable option for fabricating membranes for dye desalination under appropriate PES concentration.

In this study, the basal spacing of montmorillonite (MMT) was modified through ion exchange. Two kinds of MMT were used: sodium-modified MMT (Na-MMT) and organo-modified MMT (O-MMT). These two particles were incorporated separately into the thin-film nanocomposite polyamide membrane through the interfacial polymerization of piperazine and trimesoyl chloride in n-hexane. The membrane with O-MMT (TFNO-MMT) has a more hydrophilic surface compared to that of membrane with Na-MMT (TFNNa-MMT). When various types of MMT were dispersed in the n-hexane solution with trimesoyl chloride (TMC), O-MMT was well-dispersed than Na-MMT. The poor dispersion of Na-MMT in n-hexane led to the aggregation of Na-MMT on the surface of TFNNa-MMT. TFNO-MMT displayed a uniform distribution of O-MMT on the surface, because O-MMT was well-dispersed in n-hexane. In comparison with the pristine and TFNNa-MMT membranes, TFNO-MMT delivered the highest pure water flux of 53.15 &plusmn, 3.30 L∙m&minus, 2∙h&minus, 1 at 6 bar, while its salt rejection for divalent ions remained at 95%&ndash, 99%. Furthermore, it had stable performance in wide operating condition, and it exhibited a magnificent antifouling property. Therefore, a suitable type of MMT could lead to high separation efficiency.

Thin-film composite polyamide membranes were fabricated through cosolvent-assisted interfacial polymerization on a polyvinylidene fluoride (PVDF) hollow fiber support. An m-phenylenediamine (MPD) monomer was dissolved in an aqueous solution containing acetone of varying concentrations. Upon contact of this MPD solution with PVDF, the acetone enhanced the PVDF swelling, resulting in a higher MPD sorption. When an organic phase of toluene comprising a trimesoyl chloride (TMC) monomer was contacted with the wet PVDF, the acetone also enhanced the miscibility between water and toluene, facilitating the diffusion of MPD through the organic phase toward TMC. Hence, MPD cross-linked with TMC at a higher degree. Field emission scanning electron microscopy revealed that the formed polyamide layer grew thicker with increasing acetone concentration. The composite membrane fabricated from using 75 wt% aqueous acetone solution delivered optimal pervaporative dehydration of a 90 wt% aqueous tert-butanol solution: permeation flux = 437.2 g/m2 h; water concentration = 99.88 wt%. At varying feed temperatures and concentrations, flux increased with temperature but decreased with increasing tert-butanol content. The membrane performance on aqueous n-butanol and isobutanol feed systems was high - 93.47 and 93.37 wt% water in permeate, respectively. Overall, the composite membrane performed well on different aqueous butanol feed solutions.

In recent years, layer-by-layer self-assembly technology is one of the methods of preparing thin film composite membrane with ultra-thin selection layer. In this study, a single bilayer polyelectrolyte/hydrolyzed polyacrylonitrile (HPAN) hollow fiber membranes were fabricated by self-assembly technique for pervaporation. Branched polyethyleneimine (BPEI) and polyacrylic acid (PAA) were used as the cation polyelectrolyte and anion polyelectrolyte, respectively. Polycation/HPAN composite hollow fiber membranes were prepared by self-assembling BPEI onto the outer surface of HPAN hollow fiber membranes through electrostatic interaction. Subsequently, polycation/HPAN composite hollow fiber membranes were self-assembled with PAA to form polyanion/polycation/HPAN composite hollow fiber membranes. The effect of hydrolyzed and self-assembly on the property and pervaporation performances of aqueous ethanol solution through resulted hollow fiber membranes were investigated. By using the BPEI/PAA self-assembly, a single bilayer polyanion/polycation/HPAN composite hollow fiber membrane with excellent pervaporation performances was obtained. Furthermore, the effects of pervaporation conditions such as feed concentration, feed temperature, and downstream pressure on the pervaporation performances through BPEI/PAA/HPAN composite hollow fiber membranes were also investigated in this study.

Polydopamine (PDA) simulates the adhesive properties of mussels and modifies the surface of hydrophobic materials. In this study, the mussel-inspired deposition of PDA on a polyvinylidene fluoride support was adopted. Afterward, the catecholamine in PDA was cross-linked with trimesoyl chloride (TMC). Attenuated total reflectance-Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy validated the success of the cross-linking process. Scanning electron microscopy illustrated that the cross-linking induced the reduction of nodules. Water contact angle measurements indicated that the cross-linked membrane exhibited a higher contact angle compared with the pristine membrane. Atomic force microscopy showed that the cross-linked membrane surface was smoother than that of the membrane without cross-linking. Pervaporation tests demonstrated that the cross-linked membrane could separate water from isopropanol. Several parameters were varied: dopamine concentration, buffer solution pH, self-polymerization time, TMC concentration, cross-linking time, and annealing time. At optimum conditions, the permeate flux was 2411 ± 33 g·m−2·h−1 and the water concentration in permeate was 95.72 ± 0.44 wt% (feed = 70 wt% isopropanol at 25 °C). At a feed temperature of 70 °C, the permeate flux was 11001 ± 989 g·m−2·h−1 and the water concentration in permeate was 93.61 ± 0.45 wt%. This indicates that a composite membrane containing cross-linked PDA is stable at a high feed temperature.

In this investigation, a new concept for fabrication polyamide (PA)/polyacrylonitrile (PAN) composite hollow fiber membrane by using a triple orifice spinneret was explored. Tetraethylenepentamine (TEPA) and trimesoyl chloride (TMC) were used as the monomers of aqueous solution and acid chloride solution, respectively. The PAN dope, TEPA solution and TMC solution were pumped into the outermost, middle and inner channel of the triple orifice spinneret, respectively, and then co-extruded into water from the outlet of the spinneret simultaneously. The PA layer then was formed on the lumen surface of the synchronous wet-spun PAN hollow fiber membrane. SiO2 was added into the dope to increase the hydrophilicity of the dope. The resultant PA/PAN composite hollow fibers were characterized by using FTIR-ATR, SEM, light transmission, contact angle and positron annihilation spectroscopy (PAS). The effects of SiO2 content, TEPA concentration, as well as the TEPA solution flow rate on the properties and pervaporation performances of resultant PA/PAN composite hollow fibers were investigated. The PA layer was completely attached to the lumen surface of the resulted hollow fibers through the spinning and interfacial polymerization synchronous procedure. The pervaporation performances with 419 g/m2h of permeation flux and 96.6 wt% of water content in permeate of the 90 wt% aqueous isopropanol solution at 25 °C can be obtained through the synchronous fabricated PA/PAN composite hollow fiber membrane which was fabricated by the 18 wt% PAN dope containing 5 wt% SiO2, 1 ml/min of 14 wt% TEPA solution and 2 ml/min of 1 wt% TMC solution.

A graphene oxide (GO) nano-additive was incorporated into a polyelectrolyte complex (PEC) to prepare water selective membranes for a water desalination process. The synthesized thin film composites consisted of a PEC-GO separation layer, a microporous poly(vinylidene fluoride) layer, and a non-woven substrate. The crosslinking agent glutaraldehyde (GA) was used to enhance the stability of the PEC composite membranes. The resulting membranes were investigated in nanofiltration systems to examine their permeance and salt rejection efficiency. The results demonstrated that 100 ppm GO in the PEC exhibited a high desalination efficiency on a 1000 ppm NaCl solution. This composite exhibited permeance values in the range of 69–89 kg m−2 h−1 MPa−1 for various salt solutions. The Na2SO4 solution resulted in the highest rejection ratio of 62.1%, followed by the NaCl rejection (38.6%). The MgCl2 and MgSO4 solutions had lower rejections of 12.2% and 22.0%. It seems that the GA_PEC-GO composite was more efficient in removing divalent ions than monovalent ions, while maintaining high filtration flux.

In this study, Polyamide (PA)/polyacrylonitrile (PAN) thin-film composite (TFC) hollow fiber membranes were fabricated to investigate the dehydration performances of ethanol mixtures by pervaporation. Amine monomers (ethylenediamine (EDA), 1, 6-hexanediamine (HDA), diethylenetriamine (DETA), and tetraethylenepentamine (TEPA)) with difference number of functional groups or chain length were selected to react with trimesoyl chloride (TMC) to prepare a PA dense thin-film onto the surface of asymmetric PAN hollow fiber membranes by way of interfacial polymerization. Attenuated total reflection infrared spectroscopy (FTIR-ATR), scanning electron microscope (SEM), atomic force microscope (AFM), light transmission, contact angle and positron annihilation spectroscopy (PAS) were used to characterize the physicochemical properties, morphologies and microstructure of the PA thin layer. The pervaporation performances of aqueous ethanol solution showed the permeation flux decreased while water content in permeate increased with increasing number of amine groups. The effects of monomer concentration and reaction time on the pervaporation performances of aqueous ethanol solution through TEPA-TMC/PAN TFC hollow fiber membranes were also investigated. A 342.0 ± 22.3 g/m 2 h permeation flux and 97.6 ± 0.3 wt.% water content in permeate were obtained for the pervaporation of 90 wt.% aqueous ethanol solution at 25 °C through the PA/PAN TFC hollow fiber membrane which was fabricated by immersing PAN hollow fiber membrane into 2 wt.% TEPA aqueous solution for 1 min and then contacting 1 wt.% TMC solution for 0.5 min.

Carbon molecular sieve (CMS) membranes were prepared by controlled pyrolysis of polyetherimide (PEI) blended with polyimide (PI). The microstructure and gas separation properties of the precursor membranes and supported CMS membranes were characterized in terms of the different weight ratios of PI to PEI. The thermogravimetric analysis indicated that the co-pyrolysis in the PEI/PI appeared above 450 °C. Both permeability and selectivity of supported CMS membranes increased with increasing PI content in the precursors. The positron annihilation lifetime (PAL) results showed that the free volume size and the pore size were enhanced as the PI content is increased and that there is a close relationship between the microstructures of polymer blend precursors and CMS membranes. These results confirmed that the microstructure and gas separation performance of CMS membranes can be adjusted by blending two thermally stable polymers. For CMS membrane derived from a precursor containing 75 wt% PI and pyrolyzed at 700 °C, the gas permeance for CO2 was 40 GPU and CO2/N2 selectivity was 39.

Composite polyelectrolyte pervaporation membranes were fabricated through layer-by-layer self-assembly method. Cationic polyethyleneimine (PEI) and anionic poly(4-styrene sulfonic acid-co-maleic acid) (PSSMA) polyelectrolytes were deposited one after the other on a porous asymmetric modified polyacrylonitrile (mPAN) substrate. Attenuated total reflection–Fourier transform infrared spectral analysis and X-ray photoelectron spectrometry confirmed the deposition of polyelectrolytes on the mPAN support. Field emission scanning electron microscopy depicted that pores in the mPAN support were covered with layers of polyelectrolytes. Atomic force microscopy illustrated that the deposition of polyelectrolytes led to a smooth surface of the membrane. Moreover, the membrane exhibited improved hydrophilicity. We investigated the effect of polyelectrolyte concentrations on the efficiency of dehydrating 90 wt% aqueous alcohol solutions through pervaporation. The results established that bilayer polyelectrolyte membranes fabricated from 0.9 wt% PEI and 0.1 w% PSSMA delivered maximal dehydration efficiency.

The type of organic solvents used in interfacial polymerization affects the surface property, free volume, and separation performance of the thin-film composite (TFC) polyamide membrane. In this study, TFC polyamide membrane was fabricated through interfacial polymerization between diethylenetriamine (DETA) and trimesoyl chloride (TMC). Four types of organic solvent were explored in the preparation of pervaporation membrane. These are tetralin, toluene, hexane, and isopentane. The solubility parameter distance between organic solvents and DETA follows in increasing order: tetralin (17.07 MPa1/2) &lt, toluene (17.31 MPa1/2) &lt, hexane (19.86 MPa1/2) &lt, isopentane (20.43 MPa1/2). Same trend was also observed between the organic solvents and DETA. The larger the solubility parameter distance, the denser and thicker the polyamide. Consequently, field emission scanning electron microscope (FESEM) and positron annihilation spectroscopy (PAS) analysis revealed that TFCisopentane had the thickest polyamide layer. It also delivered the highest pervaporation efficiency (permeation flux = 860 &plusmn, 71 g m&minus, 2 h&minus, 1, water concentration in permeate = 99.2 &plusmn, 0.8 wt%, pervaporation separation index = 959,760) at dehydration of 90 wt% aqueous ethanol solution. Furthermore, TFCisopentane also exhibited a high separation efficiency in isopropanol and tert-butanol. Therefore, a suitable organic solvent in preparation of TFC membrane through interfacial polymerization enables high pervaporation efficiency.

Spherical, cubic, or rodlike hollow silica nanoparticles were embedded in nanofiltration polyamide membranes. Each nanoparticle was separately added to an n-hexane solution of trimesoyl chloride, which was reacted with piperazine through interfacial polymerization. The modified membranes exhibited higher hydrophilicity. Field emission scanning electron microscopy depicted less aggregation in the case of the embedded spherical silica nanoparticles, on account of the smallest dimensions. Moreover, the corresponding modified membrane delivered the greatest water flux. The weight ratio of the spherical nanoparticles to trimesoyl chloride was established to be optimum at 0.5, at which the membrane yielded a pure water flux of 90 ± 3 L/m2 h (6 bar), and the rejection of different salts followed this trend: Na2SO4 (92%) > MgSO4 (70%) > MgCl2 (14%) > NaCl (11%). Therefore, the shape of hollow silica nanoparticles exerts an influence on the separation efficiency of the modified nanofiltration membranes.

In this study, polyacrylic acid (PAA) was grafted onto a polyamide (PA) surface through ultraviolet-initiated graft polymerization to improve the pervaporative dehydration of aqueous alcohol solutions. The PA layer was formed on the surface of a polyacrylonitrile support by the interfacial polymerization of 1,4-bis(3-aminopropyl)piperazine and trimesoyl chloride. Afterward, the PAA was deposited under varying grafting conditions—different acrylic acid concentrations, periods of irradiation time, and irradiation distances. Attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectra indicated the presence of more carboxyl groups on the membrane surface after grafting PAA. Images from field emission scanning electron microscopy and atomic force microscopy illustrated that the membrane became rougher. PAA also improved the membrane hydrophilicity. The dehydration of 90 wt% aqueous ethanol solutions by pervaporation demonstrated that the flux and water concentration in permeate were enhanced from 803 ± 55 to 830 ± 59 g m−2 h−1 and 84.9 ± 2.5 to 99.5 ± 0.3 wt%, respectively. Furthermore, the PAA-PA membranes showed stable performance at wide operating conditions.

In this work, amorphous amino-modified silica nanoparticles (AAMSN) were successfully synthesized via the sol-gel method and combined with the polyimide (PI) 4,4′-oxydiphthalic anhydride-2,2′-bis(trifluoromethyl) benzidine (ODPA-TFMB) to prepare mixed matrix membranes (MMMs) for gas separation. The physicochemical properties of the AAMSNs were characterized by thermogravimetric analysis, X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy, and the CO2 capture and O2 enrichment behaviors of MMMs with different AAMSN contents were compared with those of a control PI membrane. The sorption isotherm and permeation data revealed that addition of AAMSNs not only increases the diffusion coefficient of the resulting membranes but also increases their adsorption coefficient due to the amorphous characteristics of the nanoparticles and good adhesion between these particles and the PI. The CO2 permeation properties and CO2/N2 selectivity of the MMM with 20 wt% AAMSN were 210.1 barrer and 30.8, respectively, while those of the control membrane were 66.7 barrer and 27.8, respectively. Mixed gas permeation results also showed that the gas permeability of the MMMs improves and their gas selectivity is maintained compared with those of the control PI membrane. The unique structure of the AAMSN/PI membrane makes it an attractive candidate for CO2 capture and O2 enrichment applications.

Nanofiltration membranes have evolved as a promising solution to tackle the clean water scarcity and wastewater treatment processes with their low energy requirement and environment friendly operating conditions. Thin film composite nanofiltration membranes with high permeability, and excellent antifouling and antibacterial properties are important component for wastewater treatment and clean drinking water production units. In the scope of this study, thin film composite nanofiltration membranes were fabricated using polyacrylonitrile (PAN) support and fast second interfacial polymerization modification methods by grafting polyethylene amine and zwitterionic sulfobutane methacrylate moieties. Chemical and physical alteration in structure of the membranes were characterized using methods like ATR-FTIR spectroscopy, XPS analysis, FESEM and AFM imaging. The effects of second interfacial polymerization to incorporate polyamide layer and &lsquo, ion pair&rsquo, characteristics, in terms of water contact angle and surface charge analysis was investigated in correlation with nanofiltration performance. Furthermore, the membrane characteristics in terms of antifouling properties were evaluated using model protein foulants like bovine serum albumin and lysozyme. Antibacterial properties of the modified membranes were investigated using E. Coli as model biofoulant. Overall, the effect of second interfacial polymerization without affecting the selectivity layer of nanofiltration membrane for their potential large-scale application was investigated in detail.

This study fabricates a transparent cyclic olefin copolymer (COC)/thermally reduced graphene oxide (TRGO) composite film with low content of TRGO, which exhibits high water vapor barrier properties. With only 0.06 wt% (0.028 vol%) TRGO, the COC/TRGO composite film reduces the water vapor permeability by ∼21%. The amount of TRGO in this work is 10–100 times lower than that in other polymer/clay or polymer/graphene composites that reduce the water vapor permeability at the same percentage. Low TRGO content has benefits of fabricating a film with low cost, high transparency, and truly excellent flexibility. The water vapor permeabilities of COC/TRGO composites are much lower than those predicted by Cussler or Nielsen model because of the significant rigidification of COC chains near TRGOs. The COC/TRGO composite film was annealed at different temperatures and then surface modified with amphiphilic polymer to further improve its barrier performance. By treating the film with 0.06 wt% TRGO, the water vapor permeability is greatly reduced by ∼65%.

The demand for flexible and transparent barrier films in industries has been increasing. Learning from nature, borate ions were used to cross-link poly(vinyl alcohol) (PVA) and graphene oxide (GO) to produce flexible, transparent high-barrier composite films with a bio-inspired structure. PVA/GO films with only 0.1 wt% GO and 1 wt% cross-linker exhibited an O2 transmission rate 85%; thus, they can be used for flexible electronics. Fourier transform infrared spectrometry and X-ray photoelectron spectroscopy indicated that the outstanding barrier properties are attributed to the formation of chemical cross-linking involving borate ions, GO sheets, and PVA, similar to the borate cross-links in high-order plants. Comparing our experimental data with the Cussler model, we found that the effective aspect ratio was significantly increased after cross-linking, suggesting that cross-linking networks connected GO with each other to form ultra-large impermeable regions. A feasible green technique, with potential for commercial production of barrier films for flexible electronics was presented.

Membrane support properties influence the performance of thin-film composite nanofiltration membranes. We fabricated several polysulfone (PSf) supports. The physicochemical properties of PSf were altered by adding polyethylene glycol (PEG) of varying molecular weights (200⁻35,000 g/mol). This alteration facilitated the formation of a thin polyamide layer on the PSf surface during the interfacial polymerization reaction involving an aqueous solution of piperazine containing 4-aminobenzoic acid and an organic solution of trimesoyl chloride. Attenuated total reflectance-Fourier transform infrared validated the presence of PEG in the membrane support. Scanning electron microscopy and atomic force microscopy illustrated that the thin-film polyamide layer morphology transformed from a rough to a smooth surface. A cross-flow filtration test indicated that a thin-film composite polyamide membrane comprising a PSf support (TFC-PEG20k) with a low surface porosity, small pore size, and suitable hydrophilicity delivered the highest water flux and separation efficiency (J = 81.1 ± 6.4 L·m-2·h-1, RNa2SO4 = 91.1% ± 1.8%, and RNaCl = 35.7% ± 3.1% at 0.60 MPa). This membrane had a molecular weight cutoff of 292 g/mol and also a high rejection for negatively charged dyes. Therefore, a PSf support exhibiting suitable physicochemical properties endowed a thin-film composite polyamide membrane with high performance.

Low permeation fluxes with high separation factors were obtained when hydrophilic dense membranes were used for the dehydration of tetrahydrofuran (THF) by pervaporation. To improve the pervaporation performance of a membrane, the polyamide thin-film composite (TFC) membranes were prepared through interfacial polymerization by reacting 1,3-diaminopropane (DAPE), 1,3-cyclohexanediamine (CHDA), or m -phenylenediamine (MPDA) with trimesoyl chloride (TMC) on the surface of a polyacrylonitrile (PAN) membrane (DAPE–TMC/PAN, CHDA–TMC/PAN, and MPDA–TMC/PAN). Pervaporation separation of an aqueous THF solution with polyamide TFC membranes was investigated as functions of diamine structure and operating conditions. Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), positron annihilation spectroscopy (PAS), and water contact angle measurements were applied to analyze the chemical structure, surface chemical composition, morphology, surface roughness, free volume, and hydrophilicity of the active polyamide layer of TFC membrane. Varying the diamine structure did affect the physicochemical properties and pervaporation performance of the polyamide TFC membranes. Compared with the CHDA–TMC/PAN and MPDA–TMC/PAN membranes, the DAPE–TMC/PAN membrane showed a lower permeation flux and a higher water concentration in permeate. This was in good agreement with the result of characterization. With an increase in the operating temperature of pervaporation, an increase in the permeation flux and a high water concentration in permeate (>99 wt%) were obtained for the DAPE–TMC/PAN membrane. It was also found that the DAPE–TMC/PAN membrane exhibited a superior performance compared with the several hydrophilic polymers and commercial inorganic membranes discussed in the literature.

Aim To investigate the influence of mineral trioxide aggregate (MTA) on angiogenesis of primary human dental pulp cells (hDPCs) via the MAPK pathway, in particular p38. Methodology Human dental pulp cells were cultured with MTA to angiogenesis, after which cell viability, ion concentration, osmolality, NO secretion, the von Willebrand factor (vWF) and angiopoietin-1 (Ang-1) protein expression were examined. PrestoBlue® was used for evaluating the proliferation of hDPCs. An enzyme-linked immunosorbent assay was employed to determine vWF and Ang-1 protein secretion in hDPCs cultured on MTA and the control. Cells cultured on the tissue culture plate without the cement were used as the control. The t-test was used to evaluate the significance of the differences between the mean values. Results Mineral trioxide aggregate elicited a significant (P

Hydrophobic composite membranes for dehydrating aqueous alcohol mixtures by pervaporation were investigated. It was suited for applications at high temperatures and for feed mixtures of water and alcohols with high number of carbon atoms. With increasing operating temperatures, pervaporation data indicated simultaneous increase in permeation flux and concentration of water in permeate. At 70 °C and for a feed mixture of 10 wt% water and 90 wt% ethanol, the composite poly(2,6-dimethyl-1,4-phenylene oxide) membrane delivered a high flux of 1333 g/(m2h) and a high permeate content of 96.4 wt% H 2 O. For a feed with higher water content, the membrane performance was further enhanced. The microstructure of the selective layer was probed with positron annihilation lifetime spectroscopy at varying temperatures. A bimodal free volume distribution was obtained, which described different shifts of free volume as temperature increased: a shift of smaller free volume to a region of much smaller free volume and a shift of bigger free volume to a region of much bigger free volume.

We prepare highly ordered flexible layers of graphene oxide (GO) on modified polyacrylonitrile substrates by the pressure-assisted self-assembly technique. This composite membrane shows excellent performance during the pervaporation separation of a 70 wt.% isopropyl alcohol (IPA)/water mixture: 99.5 wt% water in permeate and 2047 g m−2 h−1 permeation flux. Despite the specific GO deposition increase from 4.3 to 43.3 × 10−5 g cm−2 (ninefold layer thickness growth), its effect on the permeation flux is not significant, as manifested by only a little decrease in the flux. At 70 °C feed temperature, the permeate water concentration remains 99.5 wt% and the permeation flux reaches 4137 g m−2 h−1. The high selectivity may be due to the dense GO film consisting of highly ordered and packed laminates, allowing water but inhibiting IPA molecules to pass through. GO is demonstrated to be amphiphilic: water molecules adsorb first at the hydrophilic edge (hydroxides) and then rapidly diffuse through the hydrophobic core (mainly carbon), forming a water passage channel that promotes high permeation flux. When water molecules permeate through the GO layers, they accumulate and form a monolayer structure that pushes the successive layers away from each other, leading to widening of the d-spacing.

This work introduces the preparation of zeolite-filled porous mixed matrix membranes (MMMs) and discusses their potential use for air separation. Porous polysulfone (PSF) matrix membranes were prepared using the nonsolvent-induced phase separation process. Scanning electron microscope and gas permeation experiments suggested the presence of closed pores in the porous matrix membranes. Furthermore, porous MMMs containing zeolite 4A particles as filler were prepared and characterized. The permeation properties of porous MMMs were highly dependent on the zeolite content. The introduction of zeolite particles distorted the closed pores in the PSF matrix and formed nonselective voids which resulted in very high oxygen flux but low O2/N2 selectivity. The annealing technique for modifying the nonselective pores present in the polymer–zeolite interface is also described in this study. The resulting annealed porous MMMs had the ability to separate O2 from N2 more effectively than traditional dense MMMs.

Zwitterionic copolymers, poly(glycidyl methacrylate-sulfobetaine methacrylate) [poly(GMA-SBMA)], was incorporated into graphene oxide (GO) to form a GO–poly(GMA-SBMA) framework. This compound was then deposited onto a polysulfone support through pressure-assisted filtration to fabricate hybrid membranes. Optimum fabrication conditions were determined by varying the poly(GMA-SBMA) loading. Attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectroscopy confirmed the covalent bonding between poly(GMA-SBMA) and GO. On account of loading incremental amounts of poly(GMA-SBMA), the membrane thickness was increased (illustrated by field emission scanning electron microscopic images), the interlayer spacing between GO sheets was expanded (shown by X-ray diffraction patterns), and the membrane hydrophilic properties were enhanced (indicated by water contact angle data). Relative to the pristine GO membrane, hybrid membranes fabricated at optimum conditions exhibited superior separation performance (99.60 wt% water concentration in permeate and 1102 g m−2⋅h−1 permeation flux) on dehydrating a 70 wt% aqueous isopropanol solution by pervaporation. This present study explored the potential of poly(GMA-SBMA) for developing hybrid membranes with excellent pervaporation performance.

To improve the pervaporation performance in separating an aqueous ethanol solution, polyamide thin-film composite (TFC) membranes (m-tolidine-H-TMC/mPAN) were prepared through the interfacial polymerization reaction between trimesoyl chloride (TMC) and 2,2'-dimethylbenzidine hydrochloride (m-tolidine-H) on the surface of a modified polyacrylonitrile (mPAN) membrane. The effects of the feed ethanol concentration on the pervaporation performance and the durability of m-tolidine-H-TMC/mPAN TFC membranes were investigated. To choose the optimal mPAN membrane as the TFC substrate, the effect of hydrolysis time on the chemical properties and separation performance of an mPAN substrate was also studied. An appropriate hydrolysis time of 15 min was chosen to obtain the mPAN substrate due to the corresponding high permeation flux. The m-tolidine-H-TMC/mPAN TFC membrane exhibited a high pervaporation performance for ethanol dehydration. A positron annihilation lifetime spectroscopy experiment was used to estimate the mean free-volume radius of the m-tolidine-H-TMC polyamide selective layer, which lay between the radii of the water and ethanol molecules. © 2013 Society of Chemical Industry

In this study, an atmospheric pressure high temperature plasma torch (APHTPT) was used to modify poly(dimethylsiloxane) (PDMS) membranes in order to form a thin SiO x layer on the membrane surface. The chemical properties of the PDMS and APHTPT-treated membranes, as well as the conversion of polysiloxane, were determined by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray (EDX) microanalysis. The microstructure of the membranes as a function of depth was obtained with a variable monoenergy slow positron beam (VMSPB) spectroscopy. Results of XPS and EDX indicated that the conversion of polysiloxane to silica was favored with increasing plasma power. VMSPB data demonstrated that the treated membrane exhibited an asymmetric organic–inorganic hybrid structure. Based on the analysis of the treated membrane, the free-volume size increased with the depth and showed a bi-modal distribution. The gas permeation properties of O 2 , N 2 , and CO 2 were tested. The change in the applied plasma power was found to have a great effect on the membrane gas separation performance. The membrane selectivity for O 2 /N 2 and CO 2 /N 2 increased from 2.11 to 4.93 and from 9.54 to 17.19, respectively, after treatment at 10 kW. The APHTPT-treated PDMS membrane was found to have the advantages of both organic and inorganic membranes, leading to outstanding gas separation performance.

The development of the microstructure of carbon molecular sieve membranes (CMSMs) was examined using a variable monoenergy slow positron beam (VMSPB). To vary the structure of the CMSMs fabricated by pyrolyzing a Kapton precursor, different pyrolysis temperatures at a fixed heating rate under vacuum conditions and various periods of holding time at a given pyrolysis temperature were applied. The VMSPB was integrated with the platinum (Pt) capping technique, in which a layer of Pt was sputtered on the membrane surface to eliminate the back diffusion effect of positrons. On the basis of the depth profile obtained, the membranes carbonized at 800 and 900 °C were demonstrated to exhibit asymmetric microstructures at the top layer. The analysis of positron annihilation spectroscopic data of the membranes using a VEPFIT program revealed three structural layers at the most: a dense top layer, a transition layer, and an underlying layer. At prolonged holding time, it was found that the decrease in the gas permeat...

Polyamide thin-film composite (TFC) membranes were prepared by interfacial polymerization. The purpose is to improve the pervaporation performance of polyamide membranes in separating an aqueous ethanol solution. A novel amine monomer 2,2′-dimethylbenzidine hydrochloride (m-tolidine-H) was reacted with an acyl chloride monomer trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane. The effects of the following interfacial polymerization conditions on the TFC membrane pervaporation performance were investigated: monomer concentration, immersion time of mPAN in aqueous m-tolidine-H solution, and interfacial polymerization (IP) time for reacting m-tolidine-H with TMC. Attenuated total reflectance Fourier transform infrared spectroscopy and scanning electron microscopy were used to characterize the chemical structure and the morphology of the membranes, respectively. To probe the variation in the fine-structure of the polyamide active layer and the free volume depth profile in the TFC membranes, positron annihilation lifetime spectroscopy (PALS) experiments coupled to a variable monoenergy slow positron beam were conducted. The densest portion of the polyamide layer was at the interface of the two immiscible monomer solutions, as detected based on the smallest o-Ps annihilation lifetime at positron incident energies of 1 and 2 keV with 0.05 and 0.5 wt% TMC, respectively. A high pervaporation performance of 2191 g/m2h permeation flux and 99 wt% water content of permeate was delivered by the polyamide TFC membrane that was prepared by immersing the mPAN membrane in a 1.5 wt% aqueous m-tolidine-H solution for 10 s, followed by contacting it with a 0.05 wt% organic TMC solution for 10 s.

Background/purpose: β-Tricalcium phosphate (β-TCP) is an osteoconductive material which has been used for clinical purposes for several years, as is polycaprolactone (PCL), which has already been approved for a number of medical and drug delivery devices. In this study we have incorporated various concentrations of β-TCP into PCL with the aim of developing an injectable, mechanically strong, and biodegradable material which can be used for medical purposes without organic solvents. Materials and methods: This study assesses the physical and chemical properties of this material, evaluates the in vitro bioactivity of the PCL/β-TCP composites, and analyzes cell proliferation and osteogenic differentiation when using human bone marrow mesenchymal stem cells (hBMSCs). Results: The results show that weight losses of approximately 5.3%, 12.1%, 18.6%, and 25.2%, were observed for the TCP0, TCP10, TCP30, and TCP50 composites after immersion in simulated body fluid for 12 weeks, respectively, indicating significant differences (P

To improve the pervaporation performance of thin-film composite membranes, novel thin-film composite membranes were prepared via interfacial polymerization by reacting 5-nitrobenzene-1,3-dioyl dichloride (NTAC) or 5-tert-butylbenzene-1,3-dioyl dichloride (TBAC) with triethylenetetraamine (TETA) on the surface of a modified polyacrylonitrile (mPAN) membrane (TETA-NTAC/mPAN and TETA-TBAC/mPAN). The effect of the acyl chloride monomers chemical structure on the pervaporation separation of an aqueous ethanol solution was investigated. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and water contact angle measurements were applied to analyze the chemical structure, surface chemical composition, surface roughness and hydrophilicity of the polyamide active layer of the composite membrane. To correlate the variations in the free volume of the polyamide active layers with the pervaporation performance, positron annihilation spectroscopy (PAS) experiments were performed with a variable monoenergetic slow positron beam. From the results of the PAS and XPS experiments, the S parameter, o-Ps annihilation lifetime τ 3 (corresponding to free volume size) and its intensity I 3 (corresponding to free volume concentration), the τ 3 and I 3 of TETA-NTAC polyamide layer (positron incident energy of 1–1.7 keV) were both higher than those of TETA-TBAC polyamide layer. The S parameter for TETA-NTAC polyamide layer was also higher than that of the TETA-TBAC polyamide layer even though the former was more crosslinking than that of the latter. In the aqueous ethanol solution dehydration experiments, the TETA-NTAC/mPAN membrane produced both a higher permeation rate and water concentration in the permeate than the TETA-TBAC/mPAN membrane.

In this study, heat-treated polyacrylonitrile (PAN) hollow fiber membranes have been used to investigate the pervaporation performances of aqueous ethanol solution. The heat-treated PAN hollow fiber membranes were prepared by heat treating the as-spun PAN precursor hollow fiber membranes at 120, 160 and 210 °C for 12 h under air atmosphere, respectively. Scanning electron microscopy (SEM), Fourier transform infrared (FT-IR), simultaneous thermal analysis/mass spectrometry (TA/MS) and thermogravimetric analysis (TGA) are used to characterize the properties of hollow fiber membranes. The 90 wt.% aqueous ethanol solution at 25 °C has been used to investigate the pervaporation performances through hollow fiber membrane. Furthermore, in this investigation, we also use the positron annihilation spectroscopy (PAS) to identify the effect of heat-treatment on free volume variation of PAN hollow fiber membranes. To our knowledge, it is the pioneering work for PAS analysis technique used in hollow fiber membranes. The results have shown that the pervaporation performances of PAN hollow fiber membrane can be improved by heat-treatment. The permeation rate decreases while water content in permeate increases with increasing heat-treatment temperature. These phenomena might be due to that after heat-treating, the PAN hollow fiber membrane morphology becomes denser and the free volume of PAN polymer chain is reduced. Finally, heat-treated PAN/polyethylene glycol (PEG)10K blended hollow fiber membranes are also fabricated to investigate the pervaporation performance of aqueous ethanol solution. It has shown that the permeation rate as well as water content in permeate increases with increasing heat-treatment temperature. These phenomena can be interpreted that some of the PEG10K in hollow fiber membrane matrix has burnt away by heat-treating, and the occupied space of PEG10K would lead water molecules more easy to permeate. The long-term pervaporation stability of 210 °C heat-treated PAN hollow fiber membranes was also investigated in this study. It has shown that the long-term pervaporation stability can last at least 250 days.

In this study, the microstructural changes in polycarbonate (PC) membranes induced by the CO2 sorption were investigated using the CO2 sorption isotherm data and the positron annihilation lifetime spectroscopy (PALS). The effects of the PC exposure to CO2 at different temperatures and gas pressures on the free-volume distribution were discussed. The distribution at ambient conditions or 5 atm He pressure displayed a monomodal curve, whereas that at different CO2 pressures showed a bimodal curve, indicating the presence of small and big free-volume sizes due to the serious plasticization caused by CO2.

The free volume sizes and distributions and multilayer structures in asymmetric thin layer polyamide membranes in the wet state have been first time measured using the variable monoenergy slow positron beam (VMSPB). This paper presents a newly developed method which combines the technique of plasma-enhanced chemical vapor deposition to form a barrier layer for high-vacuum condition to seal the composite polyamide and of interfacial polymerization between 2-aminoethanethiol (AETH) and trimesoyl chloride (TMC) on the surface of modified asymmetric polyacrylonitrile (mPAN) membrane (AETH-TMC/mPAN), under the wet condition encountered during the pervaporation process in which they are in direct contact with the liquid environment provided by the feed solution. During the VMSPB experiments under a high vacuum, our new method maintained the thin-film composite (TFC) membrane in the wet conditions typically experienced in VMSPB experiments wherein it directly contacts the liquid feed environment, which is essent...

High-performance thin-film composite polyamide membranes for pervaporative dehydration processes were prepared by means of the interfacial polymerization of triethylenetetramine (TETA) and trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane support. The effects of annealing processes applied during and after the composite membrane preparation on the pervaporation performance were investigated. Two annealing processes were applied. One was to the composite membrane formed after the interfacial polymerization by subjecting it to different annealing temperatures and the other to the aqueous amine (TETA) solution used during the interfacial polymerization process by varying its temperature. Positron annihilation spectroscopy experiments using a slow positron beam were carried out. One of the positron annihilation techniques, Doppler broadening energy spectroscopy (DBES), was used to study the effect of the annealing processes on the S parameter (corresponding to the free volume in the membrane). The first plateau (S1 = 0.47798 ± 1.86E−4, L1 = 182 ± 84 nm) in the curve obtained for the polyamide layer in the Type-B composite membrane was higher than that (S1 = 0.47659 ± 2.74E−4, L1 = 196 ± 52 nm) in the Type-A composite membrane. In other words, this corresponds to a higher S parameter and a thinner layer for the Type-B membrane than the Type-A membrane. This implies that the free-volume amount in the former membrane is higher than that in the latter. It was found that these two annealing processes greatly improved the pervaporation separation performances of the thin-film composite polyamide membranes prepared in this study in dehydrating aqueous alcohol solutions.

To investigate the variation in the fine structure of polyamide thin-film composite (TFC) membranes prepared via two different interfacial polymerization conditions (IP-I and IP-II), experiments on Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), water contact angle, and positron annihilation spectroscopy (PAS) coupled to a slow positron beam were conducted. Polyamide TFC membranes were prepared via the interfacial polymerization reaction between triethylenetetramine (TETA) and trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane. Compared with the polyamide TFC membrane prepared via IP-I, the polyamide layer prepared via IP-II showed a shorter S plateau length (thinner thickness), a higher o-Ps intensity I3 value (higher free-volume concentration), and a smaller o-Ps lifetime τ3 value (smaller free-volume size), resulting in higher permeation rate and separation factor obtained from the pervaporative separation of a 70 wt% isopropanol aqueous solution at 25 °C.

A series of aromatic polyamide membranes for the pervaporation separation of aqueous ethanol mixtures was investigated. It was found that the permeation rate could be increased by the introduction of bulky substituted groups and arylene ether groups into the polymer backbone. The influence of the substituted group structure on the free volume in and the pervaporation performance of the aromatic polyamide membranes were systematically analyzed by positron annihilation spectroscopy (PAS) and molecular dynamics (MD) simulation. The trend of the ortho-positronium (o-Ps) lifetime and the free-volume size data evaluated by the PAS measurement and the MD simulation was highly consistent with the chemical structure of the aromatic polyamide pervaporation membranes.

A radioisotope slow positron beam has been built at the Chung Yuan Christian University in Taiwan for the research and development in membrane science and technology. Doppler broadening energy spectra and positron annihilation lifetime have been measured as a function of positron energy up to 30 keV in a polyamide membrane prepared by the interfacial polymerization between triethylenetetraamine (TETA) and trimesoyl chloride (TMC) on modified porous polyacrylonitrile (PAN) asymmetric membrane. The multilayer structures and free-volume depth profile for this asymmetric membrane system are obtained. Positron annihilation spectroscopy coupled with a slow beam could provide new information about size selectivity of transporting molecules and guidance for molecular designs in polymeric membranes.

High-performance polyamide thin-film composite membranes were successfully prepared using interfacial polymerization of triethylenetetramine (TETA) and trimesoyl chloride (TMC) on the surface of a modified polyacrylonitrile (mPAN) membrane for alcohol dehydration by pervaporation. Attenuated total reflection infrared spectroscopy (FTIR-ATR), scanning electron microscope (SEM), atomic force microscope (AFM) and the contact angle were used to characterize the chemical structures, morphologies and hydrophilicity of the composite membrane active layers. The best pervaporation performance was achieved by using the TETA–TMC/mPAN composite membrane that is prepared by immersing mPAN in 0.1 wt.% aqueous TETA solution for 5 s and then contact with 0.05 wt.% organic TMC solution for 10 s. The pervaporation separation of a 70 wt.% isopropanol–water mixture through the composite membrane with the ultra thin polyamide layer at 70 °C, the permeation rate and water concentration in permeate were 3.4 kg/m2 h and higher than 99 wt.%, respectively. It was also found that TETA–TMC/mPAN exhibited superior performance to the composite membranes discussed in the literature.

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 ...