Thin Polyamide Films Research Articles

Development of Polyamide-Modified Membranes for Solar-Driven Seawater Desalination System

In response to the escalating global water crisis, this study introduces the development of polyamide-modified membranes (PA-PES, PA-PP, and PA-PTFE) through interfacial polymerization to enhance the efficiency of a passive solar desalination system. FTIR analysis and morphological characterization showed that a thin polyamide film formed above the modified membranes using m-phenylene diamine (MPD) and trimesoyl chloride (TMC). Notable improvements were observed in its productivity and distillate salinity by integrating these modified membranes into the membrane distiller of the system. Mainly, the PA-PES membrane achieved productivity of 764.56 ml/m2-h and reduced salinity to as low as 2 g NaCl/L. Despite challenges in salinity reduction, possibly due to residual chlorides, this study demonstrates the potential of polyamide-modified membranes in advancing solar-driven desalination, offering a promising solution to mitigate global water scarcity. This research paves the way for further advancements in sustainable desalination technology, emphasizing the need for continued optimization and exploration of membrane-based systems.

Energy harvesting from acid mine drainage using a highly proton/ion-selective thin polyamide film

A huge chemical potential difference exists between the acid mine drainage (AMD) and the alkaline neutralization solution, which is wasted in the traditional AMD neutralization process. This study reports, for the first time, the harvest of this chemical potential energy through a controlled neutralization of AMD using H+-conductive films. Polyamide films with controllable thickness achieved much higher H+ conductance than a commercially available cation exchange membrane (CEM). Meanwhile, the optimal polyamide film had an excellent H+/Ca2+ selectivity of 63.7, over two orders of magnitude higher than that of the CEM (0.3). The combined advantages of fast proton transport and high proton/ion selectivity greatly enhanced the power generation of the AMD battery. The power density was 3.1 W m–2, which is over one order of magnitude higher than that of the commercial CEM (0.2 W m–2). Our study provides a new sustainable solution to address the environmental issues of AMD while simultaneously enabling clean energy production.

Energy broadening of neutron depth profiles by thin polyamide films

Energy broadening of neutron depth profiles by thin polyamide films

Preparation and Properties of Thin-Film Composite Forward Osmosis Membranes Supported by Cellulose Triacetate Porous Substrate via a Nonsolvent-Thermally Induced Phase Separation Process.

A porous substrate plays an important role in constructing a thin-film composite forward osmosis (TFC-FO) membrane. To date, the morphology and performance of TFC-FO membranes are greatly limited by porous substrates, which are commonly fabricated by non-solvent induced phase separation (NIPS) or thermally induced phase separation (TIPS) processes. Herein, a novel TFC-FO membrane has been successfully fabricated by using cellulose triacetate (CTA) porous substrates, which are prepared using a nonsolvent-thermally induced phase separation (N-TIPS) process. The pore structure, permeability, and mechanical properties of CTA porous substrate are carefully investigated via N-TIPS process (CTAN-TIPS). As compared with those via NIPS and TIPS processes, the CTAN-TIPS substrate shows a smooth surface and a cross section combining interconnected pores and finger-like macropores, resulting in the largest water flux and best mechanical property. After interfacial polymerization, the obtained TFC-FO membranes are characterized in terms of their morphology and intrinsic transport properties. It is found that the TFC-FO membrane supported by CTAN-TIPS substrate presents a thin polyamide film full of nodular and worm-like structure, which endows the FO membrane with high water permeability and selectivity. Moreover, the TFC-FO membrane supported by CTAN-TIPS substrate displays a low internal concentration polarization effect. This work proposes a new insight into preparing TFC-FO membrane with good overall performance.

Toward Enhancing Desalination and Heavy Metal Removal of TFC Nanofiltration Membranes: A Cost-Effective Interface Temperature-Regulated Interfacial Polymerization.

Polyamide (PA) chemistry-based nanofiltration (NF) membranes have an important role in the field of seawater desalination and wastewater reclamation. Achieving an ultrathin and defect-free active layer via precisely controlled interfacial polymerization (IP) is an effective routine to improve the separation efficiencies of NF membranes. Herein, the morphologies and chemical structures of the thin-film composite (TFC) NF membranes were accurately regulated by tailoring the interfacial reaction temperature during the IP process. This strategy was achieved by controlling the temperature (-15, 5, 20, 35, and 50°) of the oil-phase solutions. The structural compositions, morphological variations, and separation features of the fabricated NF membranes were studied in detail. In addition, the formation mechanisms of the NF membranes featuring different PAs were also proposed and discussed. The temperature-assisted IP (TAIP) method greatly changed the compositions of the resultant PA membranes. A very smooth and thin PA film was obtained for the NF membranes fabricated at a low interfacial temperature; thus, a high 19.2 L m-2 h-1 bar-1 of water permeance and 97.7% of Na2SO4 rejection were observed. With regard to the NF membranes obtained at a high interfacial temperature, a lower water permeance and higher salt rejection with fewer membrane defects were achieved. Impressively, the high interfacial temperature-assisted NF membranes exhibited uniform coffee-ring-like surface morphologies. The special surface-featured NF membrane showed superior separation for selected heavy metals. Rejections of 93.9%, 97.9%, and 87.7% for Cu2+, Mn2+, and Cd2+ were observed with the optimized membrane. Three cycles of fouling tests indicated that NF membranes fabricated at low temperatures exhibited excellent antifouling behavior, whereas a high interface temperature contributed to the formation of NF membranes with high fouling tendency. This study provides an economical, facile, and universal TAIP strategy for tailoring the performances of TFC PA membranes for environmental water treatment.

Thin film composite membranes: Does the porous support truly have negligible resistance?

The permeation resistance of the porous support in a thin film composite (TFC) membrane is believed to be negligible compared with that of the thin polyamide film. Indeed, the resistance of a porous support, as determined from direct water permeation experiments as a function of transmembrane pressure (TMP), is only a fraction of the total resistance of a typical TFC membrane. However, the true resistance of the porous support in a TFC membrane, especially during high-pressure reverse osmosis (RO), could be significantly different from the value obtained via direct permeation measurement. Although the porous support is subjected to mechanical loading equivalent to the overall TMP, the effective TMP across the porous support that generates deformation can be significantly lower due to the internal pressure of the water within the pores. In this study we utilized a serial configuration, consisting of a TFC membrane on top of a representative porous support, to quantify the true resistance of the porous support under conditions of high mechanical loading but low permeation. Unsurprisingly, the results confirm that the porous support resistance appears negligible as compared with that of the TFC membrane under low TMP. However, after exposure to high TMP in the serial configuration, the porous support evidences up to 15X larger plastic strain and 28X higher resistance as compared to the same support tested separately under low TMP. At TMP = 8.3 MPa, the additional porous support beneath the TFC membrane increases the overall resistance by 31%. Using a resistance in-series model, the data suggest that the true resistance of the porous support could be as high as ~ 45% that of the thin film under the high-TMP but low-permeation condition encountered during high-pressure RO desalination.

Relating the performance of sulfonated thin-film composite nanofiltration membranes to structural properties of macrovoid-free polyethersulfone/sulfonated polysulfone/O-MWCNT supports

Sulfonated thin-film composite nanofiltration (TFC NF) membranes were produced on macrovoid-free polyethersulfone/sulfonated polysulfone/oxidised multi-walled carbon nanotube (PES/SPSf/O-MWCNT) supports via an interfacial polymerisation method. The aqueous phase solution consisted of a mixture of piperazine (PIP) and 2,4-diaminobenzene sulfonic acid (2,4-DABSA) and the organic phase solution consisted of trimesoyl chloride (TMC). The TFC NF membranes fabricated on the PES/SPSf/O-MWCNT supports showed a 35% improvement in pure water flux with comparable salt rejections from those prepared on PES/SPSf supports. The presence of hydrophilic O-MWCNTs in the PES/SPSf supports resulted in the formation of a thin polyamide film on the surface of the support with enhanced water permeability and salt rejection. The addition of low monomer weight ratio of 2,4-DABSA in the diamine aqueous mixture led to the generation of sulfonated TFC NF membranes with superior membrane performance in terms of pure water permeability (30.2 L/m2·h·bar), monovalent/bivalent salt selectivity (αNaCl/Na2SO4 = 25.0) at low operating pressures (3 bar) and at salt concentrations in the range of brackish waters. Moreover, the fabricated sulfonated TFC NF membranes exhibited good antifouling properties against bovine serum albumin, with a flux recovery ratio of 96.4% obtainable after three cycles of fouling and cleaning. The performance of the sulfonated TFC NF membranes remained fairly stable over a 10-day period of pure water flux and Na2SO4 salt rejection testing. The fabricated sulfonated TFC NF membranes displayed promising features for use as pre-treatment membranes for lower-pressure water softening and desalination of brackish water.

Quantitative Characterization of a Desalination Membrane Model System by X-ray Photoelectron Spectroscopy.

Aromatic polyamide films form the active layer in reverse osmosis desalination membranes. Despite widespread use of this technology, it suffers from low rejection rates for certain water contaminants and from membrane fouling. Through a better understanding of the fundamental surface chemical processes during reverse osmosis desalination, advances in membrane and material design are expected. The recent invention of a molecular layer-by-layer (mLbL) preparation technique [ Johnson , P. M. ; Molecular Layer-by-Layer Deposition of Highly Crosslinked Polyamide Films . J. Polym. Sci., Part B: Polym. Phys. 2012 , 50 ( 3 ), 168 - 173 ] yields films that are sufficiently smooth to warrant investigation with high-resolution microscopy and spectroscopy methods. We present high-resolution, quantitative X-ray photoelectron spectroscopy (XPS) data on the surface chemistry of ultrathin polyamide films that can serve as a model system for desalination membranes. We show that a quantitative analysis of the XPS spectra gives information about the functional groups of the film as well as other compounds present due to the synthesis under ambient conditions. Unpolymerized functional groups are identified and aid in understanding the degree of cross-linking. Investigation of polymers with synchrotron-based XPS requires taking beam-induced changes into account. We quantify X-ray beam damage and show that beam damage to the polyamide is limited, allowing long-term investigation of thin polyamide films. Characterizing mLbL-grown films via high-resolution XPS is the basis for a better understanding of the chemical interplay of polyamide surface functional groups with the major components of desalination systems.

Improved water management using subsurface membrane irrigation during cultivation of Phaseolus vulgaris

Subsurface membrane irrigation systems, controlled by changes in the water potential in the soil-plant-atmosphere continuum, were used to cultivate Phaseolus vulgaris over a full growth cycle (64 days). Membrane irrigation systems used a thin polyamide film supported on either a woven hydrophilic support (FO-TFC treatment) or a non-woven hydrophobic support (RO treatment). Water use efficiency was assessed using leaf biomass per unit irrigation water and compared to conventionally irrigated plants (control). Additionally, gas exchange and fluorescence parameters, as well as stable isotopes, were used to assess the plants’ physiological status. Soil water content over the growth cycle was maintained at 0.7 cm3 cm−3 under control conditions and declined from 0.6 to 0.12 cm3 cm−3 during plant growth, below residual moisture content, under both FO-TFC and RO membrane irrigation. Notwithstanding this, the total leaf dry matter was statistically equivalent for control plants (38.4 g) and FO-TFC treated plants (29.6 g) and approximately 68% lower for RO treated plants. The internal over external carbon concentration (Ci/Ca) in the leaves and efficiency of open Photosystem II reaction centres in the light (Fv'/Fm') were statistically equivalent in membrane treatments and control plants. Similarly, carbon (δ13C) and nitrogen (δ15N) isotope composition, as well as %N, of green bean pods and leaves were statistically equivalent for plants grown on FO-TFC and control, indicating no effect on beans protein content. Total bean production per parcel and plant water use efficiency (WUE) for conventional irrigation (0.24 kg at 10.2 kg m−3 WUE) was statistically equivalent to plants grown on FO-TFC treatment (0.19 kg at 12.8 kg m−3 WUE). Although the WUE for RO treatment (11.4 kg m−3) was statistically equivalent to control, the total bean production per parcel was significantly lower (0.07 kg). Results indicate that subsurface membrane irrigation may be a solution for improved water management without compromising yield production and quality.

Characterizing salt permeability in polyamide desalination membranes using electrochemical impedance spectroscopy

Improving the performance of desalination membranes requires better measurements of salt permeability in the polyamide separating layer to elucidate the thermodynamic and kinetic components of membrane permselectivity. In this work, electrochemical impedance spectroscopy (EIS) is introduced as a technique to measure the salt permeability and estimate the salt partition coefficient in thin polyamide films created using molecular layer-by-layer deposition. The impedance of supported polyamide films ranging in thickness from 3.5 nm to 28.5 nm were measured in different electrolyte solutions. Impedance spectra were modeled with equivalent circuits containing resistive and capacitive elements associated with the EIS measurement system as well as characteristic low-frequency parallel resistive and capacitive elements that are associated with the polyamide film. The characteristic polyamide membrane resistance increases with film thickness, decreases with solution concentration, and is an order of magnitude greater for a divalent cationic solution than for a monovalent cationic solution. For each polyamide film, salt permeability is calculated from the membrane resistance, and a salt partition coefficient is estimated. At the highest solution concentration measured, which is representative of brackish water desalination conditions, the calculated salt permeabilities range from Ps = 1.3×10−16 ms−1 to 3.9×10−16 m s−1, and the estimated salt partition coefficients range from Ks = 0.008 to 0.016. These measurements demonstrate that EIS is a powerful tool for studying membrane permselectivity through the measurement of salt permeability in thin polyamide films.

Nanofoaming of Polyamide Desalination Membranes To Tune Permeability and Selectivity

Recent studies have documented the existence of discrete voids in the thin polyamide selective layer of composite reverse osmosis membranes. Here we present compelling evidence that these nanovoids are formed by nanosized gas bubbles generated during the interfacial polymerization process. Different strategies were used to enhance or eliminate these nanobubbles in the thin polyamide film layer to tune its morphology and separation properties. Nanobubbles can endow the membrane with a foamed structure within the polyamide rejection layer that is approximately 100 nm in thickness. Simple nanofoaming methods, such as bicarbonate addition and ultrasound application, can result in a remarkable improvement in both membrane water permeability and salt rejection, thus overcoming the long-standing permeability–selectivity trade-off of desalination membranes.

Thin Film Polyamide Membranes with Photoresponsive Antibacterial Activity

AbstractMembranes containing a photosensitizer molecule as part of the selective layer are proposed with demonstrated anti‐biofouling activity. For the membrane preparation, mixtures of an amine‐functionalized photosensitizer molecule, (5,10,15,20‐(tetra‐4‐aminophenyl)porphyrin) and m‐phenylene diamine (MPD) reacted with trimesoyl chloride (TMC) by interfacial polymerization to form thin polyamide films on top of an asymmetric porous support. A highly permeable membrane (35.4 Lm−2h−1bar−1) with 99 % rejection of Brilliant Blue R (826 g/mol) was obtained using 0.25 wt% porphyrin and 0.75 wt% MPD as amine monomers. Under visible light exposure, singlet oxygen (1O2) is generated in the porphyrin containing‐polyamide film, reaching the bacteria in the feed by diffusion and enhancing the biofouling resistance and anti‐microbial activity. Anti‐biofouling and anti‐microbial photoactivity in solution are demonstrated on Staphylococcus aureus at different porphyrin concentrations and light exposure time.

Exploratory Experiments in Recording on Sputtered Magnetic Tape at an Areal Density of 148 Gb/in<inline-formula> <tex-math notation="LaTeX">$^{\textbf 2}$ </tex-math></inline-formula>

A sputter deposited CoPtCr-SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> perpendicular recording media with excellent orientation was successfully grown on a thin polyamide film. Using 32-channel GMR tape heads and advanced hard-disk drive heads, the recording performance and durability of this media was investigated. These studies demonstrated an unprecedented broadband signal-to-noise ratio of 17 dB at 896 kb/in using a 77 nm-wide TMR reader, corresponding to an estimated 148 Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> recording density, and provided a preliminary assessment of durability exceeding current tape media specifications.

Characterization of ion transport in thin films using electrochemical impedance spectroscopy: I. Principles and theory

The paper presents the principle and theoretical basis for application of electrochemical impedance spectroscopy (EIS) to study ion transport and partitioning in thin films or membranes supported by a solid electrode and exposed to an electrolyte solution. It is shown that the equivalent circuit is in general composed of two parallel branches: one corresponds to transient charge transfer processes, in which all ions (both electrochemically active and inactive) participate, and the other to the diffusion and reaction of electroactive ions only. Among the experimentally accessible parameters three appear to be of particular relevance to ion transport: (a) the high-frequency resistance of the film directly related to the sum of permeabilities of all mobile ions in the membrane including counter-ions bound to the fixed charges, (b) the diffusion impedance of the electroactive ion that is capable of separately retrieving the values of diffusion and partitioning coefficient of the specific ion and (c) dielectric capacitance of the film, which may yield the effective thickness of the film, particularly interesting if the membrane is not homogeneous. Such information may be highly relevant to analysis of ion exclusion mechanisms in the film and provide inputs to computational models of ion transport in membranes. Experimental examples involving thin polyamide films are provided to partly illustrate the use of equivalent circuit, data analysis and possible artifacts.

Use of Attenuated Total Reflection Infrared Spectroscopy for Analysis of Partitioning of Solutes between Thin Films and Solution

The paper examines attenuated total reflection (ATR) spectroscopy as a tool for quantifying the partitioning of small molecular species between a solution and a thin film, while the film is directly exposed to the solution for equilibration. For the case of a thin film having a thickness substantially smaller than the decay length of the evanescent wave, we developed suitable linear relationships that relate the measured absorption of the characteristic band to the concentration of the species under study in the film and in solution. In the application of ATR-Fourier transform infrared spectroscopy, the method is particularly suitable for films a few tens to hundreds of nanometers thick and for solutes that preferentially partition into the film. As an example, the partitioning isotherm of 1-pentanol between water and a thin polyamide film separated from a reverse osmosis membrane was determined experimentally, and the limitations of the method are discussed.

Synthesis and Characterization of Electrochromic Polyamides with Well‐Defined Molecular Structures and Redox Properties

AbstractIn this paper we report the synthesis and characterization of a series of electrochromic polyamides (alternating copolymers). The synthesis proceeds via the condensation polymerization between amine‐capped oligoaniline and acyl chlorides such as isophthaloyl dichloride, terephthaloyl chloride, azelaoyl chloride, and dodecanedioyl dichloride. Both the orthogonal tert‐butoxycarbonyl (BOC) group on the oligoaniline segment and the non‐conjugated aromatic or aliphatic segment on the polymer backbone play a vital role in the formation of the final polyamides with good solubility in common organic solvents. We cast thin polyamide films from their chloroform solutions and studied their electrochemical behavior and spectroscopic properties. In contrast to the polyaniline, the copolymers bearing oligoaniline segments show four distinct oxidation states, which were fully characterized using IR and UV‐vis spectroscopy. The copolymer thin films also exhibit electrochromic behavior when a linear potential sweep is applied. Compared with the polyaniline, the polyamides adhere much more strongly to the indium tin oxide (ITO) coated glass and show no signs of delamination after hundreds of redox cycles in a hydrochloric acid solution. We believe that these factors make these novel polyamides very attractive as electrochromic materials.

Crystallinity measurements of polyamides adsorbed as thin films

The crystallinity degree of thin polyamide films (PA66, 610 and 612) spin coated on four types of substrates are estimated. Two original methods based on the analysis of infrared spectra are proposed. The high sensitivity of polarization modulation reflection-absorption spectroscopy for the study of thin polymer films leads to quantitative results. These two methods offer the possibility to estimate the degree of crystallinity by using infrared spectroscopy, independently of any other technique, if the crystallinity degree in the isotropic bulk state is known. Polyamides are spin coated, on the one hand, on inert and highly reflecting gold substrates, and on the other hand, on the same gold substrates grafted with different chemical functionality. Our calculations show a lower crystallinity degree for inert substrate and higher values for functionalized systems with respect to the bulk. These results suggest that the surface chemical grafts not only play the role of nucleation seeds, but also affect the crystalline morphology as seen by atomic force microscopy.

The effect of fiber coating on the tensile properties of ionomer‐based composites

AbstractAsbestos fibers, of the chrysotile variety, were coated with a thin polyamide film by an in situ polycondensation technique. Ionomer‐based composites were prepared containing the so‐modified asbestos fibers in a random in‐plane orientation; results of testing the tensile properties of these asbestos/polyamide/ionomer composites are presented. Parameters investigated comprise the asbestos content in the composite and the polyamide content deposited on asbestos. A significant improvement in the tensile performance was established, especially at the intermediate polyamide content of 3.4 phr. The behavior is discussed in terms of possible interactions between the phases present in the composite material.

Chromatography in thin polyamide films

The applicability of Russian-made samples of polyamide for use as sorbents for the separation of some amino acid derivatives has been shown.