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The influence of substrate topography and interfacial polymerization (IP) conditions were investigated during the fabrication of patterned thin-film composite (TFC) membranes. Aromatic and semi-aromatic polyamide layers were formed atop patterned ultrafiltration (UF) membrane supports by IP using different concentrations of m-phenylenediamine (MPD) or piperazine (PIP) in water of 0.01–2% w/v with a fixed concentration of trimesoyl chloride in hexane of 0.1% w/v. For all the conditions evaluated, TFC membranes with regular surface patterns were achieved by maintaining amine soaking time and IP reaction time within 120 s. Importantly, the surface topography of the patterned TFC membranes was determined to be independent of IP reaction time. Characterization of the morphological details suggests non-conformal growth of the barrier layer on the patterned UF substrates. Results indicate that the extent of such non-conformal growth can be reduced by decreasing the amine concentration as well as by choosing an amine monomer such as PIP that produces a thinner semi-aromatic barrier layer. The overall findings of this study provide a means for achieving desired surface features for specific membrane applications. [ABSTRACT FROM AUTHOR]

Previous work has suggested that membrane patterning is a promising approach to fouling mitigation. In this systematic study, we describe performance metrics for the cross-flow filtration of colloidal suspensions through ultrafiltration membranes with lithographically patterned surfaces. The effects of particle size, cross-flow velocity, pattern size, and flow configuration on membrane performance are specifically considered. Using an unpatterned membrane as a reference, results show that the presence of surface patterns increases the critical flux associated with filtration of colloidal feed solutions. For the patterned membranes, the critical flux increases with particle size, cross-flow velocity, the angle between the feed flow and the pattern lines, and the pattern height. These experimental findings can be correlated with a back-transport mechanism such as shear-induced diffusion, which ultimately increases the threshold permeation flux associated with the onset of particle deposition. [ABSTRACT FROM AUTHOR]

Abstract: Thin film composite (TFC) membranes are critical components for reverse osmosis (RO) and nanofiltration (NF) processes. Similar to other liquid-based filtration membranes, TFC membranes are susceptible to concentration polarization and fouling/scaling. Recently, surface topography modification has been shown as a potential approach for fouling mitigation. However, for TFC membranes, tailoring the surface topography remains a challenge. Here, we demonstrate for the first time, successful fabrication of a patterned TFC membrane. A two-step fabrication process was carried out by (1) nanoimprinting a polyethersulfone (PES) support, and (2) forming a thin dense film atop the PES support via interfacial polymerization (IP) with trimesoyl chloride and 1,3-phenylenediamine solutions. Chemical, topographic, and permeation characterization was performed on the imprinted IP membranes, and their permselectivity was compared with that of a flat (non-imprinted) TFC membrane prepared using the same IP procedure. [Copyright &y& Elsevier]

Abstract: Synthetic membranes are used in applications such as controlled drug release, artificial organs, smart sensors, and water treatment that require knowing the pore-size distribution (PSD). Current PSD characterization methods can require dedicated and/or expensive equipment as well as special expertise to implement. Evapoporometry (EP) is a novel characterization technique based on vapor pressure depression that can accurately determine the pore size for ultrafiltration membranes using a simple diffusion cell and a microbalance. A straightforward characterization procedure and comprehensive error analysis are described. EP characterization of the PSD of a 100nm bilayer Anopore™ membrane used as a standard is shown to compare favorably with the nominal pore diameter, FESEM analysis, and analyses reported by prior investigators. In addition, EP is utilized for PSD characterization of commercially fabricated 20 and 50nm polyvinylidene fluoride (PVDF) membranes for which the results are compared with those obtained via liquid displacement porometry (LDP). The mean pore diameters determined by EP and LDP are in good agreement for the 50nm PVDF membranes, but the lower values obtained via LDP for the 20nm PVDF membranes may reflect the effects of high pressures that are not required in EP. The advantages and limitations of EP as well as other potential applications of this technique are discussed. [Copyright &y& Elsevier]

Abstract: A model for the dry-casting process for polymeric membrane formation is generalized to include a broader spectrum of boundary conditions. This model is used to conduct a sensitivity analysis to assess which properties and process parameters are most influential and hence need to be determined most accurately. The model predictions are relatively insensitive to changes in the nonsolvent/polymer and nonsolvent/solvent friction coefficients but moderately sensitive to changes in the solvent/polymer friction coefficient. However, the predictions are very sensitive to changes in the gas-phase mass-transfer coefficient, which needs to be well-characterized and carefully controlled during the dry-casting process. Experimental studies for the water/acetone/cellulose acetate system demonstrate that changes in the boundary conditions can result in dramatically different membrane morphologies. The results of the modeling, sensitivity analysis and experimental studies are used to advance a simple phenomenological model for the dry-casting process that explains all the observed trends. This is used to develop a set of design heuristics for dry-casting based on the effect of changes in the properties and parameters on the casting solution and gas-phase mass-transfer resistances, the solvent concentration at the interface and the mass-transfer rate. [Copyright &y& Elsevier]

Abstract: The summative and formative fouling potential of industrial fermentation broth engineered to produce valuable industrial enzymes was investigated. A resistance-in-series approach was adapted to estimate the relative fouling potential of broth components at two different cross-flow conditions under high-loading scenarios. Bench-scale tests were executed in cross-flow cell modules fitted with polysulfone microfiltration (MF) membranes (0.2μm nominal pore size) where fermentation broth and its isolated components, i.e., bacterial cells, particle-free media, surrogate proteins, or virgin media, were separately introduced. Setting and fouling behavior were assessed in situ, using continuous ultrasonic and permeate flow observations. Fouled membranes were characterized using scanning electron microscopy (SEM) and scanning acoustic microscopy (SAM). The largest flux declines were observed when membranes were challenged with fresh industrial broth. Flux was least affected by virgin media that had been clarified by centrifugation and by a solution of washed bacterial cells. Acoustic spectra showed significant increases in reflected power immediately following broth challenges. Above a threshold of 14μgcm−2, SAM showed that acoustic reflection patterns from fouled membranes were statistically different than their otherwise clean-condition counterparts. SEM observations were consistent with acoustic spectra and biochemical autopsy revealing rapid, progressive biomass build-up from dynamic conglomeration of “patchy”, heterogeneous biomass deposits that are loosely anchored to the membrane surface. Results were interpreted via modeling approaches using resistance-in-series as well as combined pore-blockage and cake filtration. [Copyright &y& Elsevier]

Abstract: A homologous series of thin film composite (TFC) membranes was made by interfacial polymerization (IP) of trimesoyl chloride (TMC) and m-phenylenediamine (MPD). Membrane flux and rejection as well as the chemical and mechanical properties of the unsupported IP film were evaluated as a function of monomer concentration. The surface characteristics of the IP films were determined using electron-spectroscopy-for-chemical-analysis (ESCA) and contact angle measurements, and the mechanical properties were obtained using pendant drop mechanical analysis (PDMA) and surface profilometry. Results indicate that the TMC concentration has a more pronounced effect on the IP film properties than the MPD concentration. Higher TMC concentration leads to a pronounced increase in the IP film thickness and surface hydrophilicity. In contrast, the thickness increase is smaller and surface hydrophilicity decreases when the MPD concentration is increased. Water flux was determined to depend mainly upon the IP film thickness and surface hydrophilicity whereby these two parameters have counterbalancing effects. Consequently, the decrease in water flux with increasing MPD concentration is pronounced, but a corresponding increase in the TMC concentration has a smaller effect. These studies provide an improved basis for understanding the factors that govern TFC membrane performance. [Copyright &y& Elsevier]

Abstract: A major concern with the use of polyamide thin film composite (TFC) membranes is their loss of performance when exposed to oxidizing agents such as aqueous chlorine that is used in membrane cleaning and water disinfection. A better understanding of this oxidative degradation process would facilitate the development of improved TFC membranes. This study utilizes pendant drop mechanical analysis (PDMA) to measure chlorine-exposure-induced changes in the behavior of polyamide barrier-layers formed by the interfacial polymerization (IP) of m-phenylenediamine (MPD) and trimesoyl chloride (TMC). PDMA enables the measurement of mechanical and transport properties of unsupported MPD–TMC thin films. Based upon the PDMA results as well as those obtained from experiments conducted on commercial TFC RO membranes, a hypothesis is presented describing a two-pathway mechanism for the chlorine degradation of polyamide TFC membranes. At a constant pH, a morphology change, not polymer chain scission, occurs leading to separation of the barrier layer from the support. A second degradation pathway is observed when chlorine exposure under acidic conditions is followed by exposure of the polyamide thin-film to caustic (pH >11) conditions. The results of this investigation provide a strong rationale for further refinement of the PDMA methodology for use in basic studies as well as for screening applications that could aid in the development of chlorine-resistant IP thin films. [Copyright &y& Elsevier]

This paper describes the development of an ultrasonic technique for the characterization of membrane morphology. Ultrasonic frequency-domain reflectometry (UFDR) using a 90 MHz focused immersion transducer has been employed to obtain characteristic acoustic responses from microporous polymeric membranes with nominal pore sizes in the range of 0.1–0.6 μm. Systematic and statistically significant differences in signal amplitude are observed in the frequency domain for reflections from the back surface of poly(vinylidene fluoride) (PVDF) and mixed cellulose ester (MCE) membranes. As the pore-size of the membranes increases, the amplitude of the reflected signal at high frequencies decreases due to increased scattering of the ultrasonic wave. These UFDR differences correspond well with those obtained from independent measurements including scanning electron microscopy (SEM) and gas–liquid porometry. A simple phenomenological artificial neural network (ANN) model has been developed to predict membrane pore-size based upon the signal amplitude at five frequencies. Such predictive capability suggests that the combination of UFDR and ANN may have significant utility for membrane quality control applications. [Copyright &y& Elsevier]

Poly(vinylidene fluoride) (PVDF) membranes fabricated from conventional processes have a limited range of microstructures. For example, PVDF membranes with spherulitic and isotropic microstructures containing macrovoids are extremely difficult to avoid using standard casting techniques such as wet-casting and thermally induced phase-separation (TIPS) casting. In order to create novel PVDF membrane microstructures such as a spongy, open-celled structure, a new membrane-formation process with six independent process parameters has been developed. Because this new process, thermally assisted evaporative phase separation (TAEPS), has a large number of parameters, the membrane microstructures are easily changed. The TAEPS process can fabricate a PVDF membrane with a spongy, anisotropic microstructure without macrovoids using a simple ternary system with no additives. In addition to studying the novel and unique microstructures available with the TAEPS process, the relationship between final morphology, performance, and processing conditions has been investigated in this paper. [Copyright &y& Elsevier]

Poly (ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene with an excellent combination of chemical, thermal and mechanical properties. Although the lack of a suitable solvent for ECTFE precludes membrane casting by conventional room-temperature processes of immersion precipitation or evaporative casting, thermally induced phase separation provides an attractive pathway for membrane fabrication. We have successfully identified three possible latent solvents for ECTFE and have studied the ECTFE-dibutyl phthalate (DBP) polymer-diluent system. ECTFE membranes were fabricated using a TIPS-casting apparatus that allowed control of several important process parameters. ECTFE membranes were characterized via scanning electron microscopy (SEM), porometry and permeation techniques. Results indicated that membranes with continuous pores having diameters in the microfiltration range (0.1–0.5 μm) could be reliably fabricated. [Copyright &y& Elsevier]

Investigates macrovoid growth in dry-cast polymeric membranes. Solutocapillary convection hypothesis; Solvent/non-solvent ratio; Videomicroscopy flow-visualization.

The Solutocapillary Convection (SC) hypothesis contends that macrovoid (MV) growth in dry-cast membranes is governed by a solutal-Marangoni convection-induced force caused by the rapid evaporation of volatile solvent from the liquid/gas interface, a viscous drag force, and a gravity-induced buoyancy force. Two different sets of experiments using the cellulose acetate-acetone-water system were conducted to test the SC hypothesis. Membranes were cast aboard a KC-135 aircraft that enabled short periods of microgravity (∼0-g) as well as 2-g conditions. The studied process variables included the solvent/non-solvent (S:NS) ratio, surface tension, and the magnitude of the body force (buoyancy). SEM analysis of the resulting membrane morphologies indicated that the MV morphology was strongly influenced by the S:NS ratio. However, dependence of MV size and number density on the buoyancy force could not be established. In the second set of experiments, videomicroscopy flow-visualization (VMFV) was utilized to measure fluid velocities at the MV/casting-solution interface and in the bulk solution. The magnitude of the solutocapillary convection was controlled via surfactant additions. A comparison of the ratio of the edge to the bulk velocity for MVs made from surfactant-free and surfactant-containing casting solutions did not provide evidence of a statistically significant surfactant effect. However, the presence of the surfactant did affect the MV number density. In addition, the presence of tracer particles inside the MVs indicated that a convective flow enables their transfer from the bulk to the interior of the MV. [Copyright &y& Elsevier]

Experiments were conducted onboard a NASA KC-135 aircraft in order to assess the validity of two hypotheses proposed for the growth of macrovoid (MV) pores formed during the dry-casting of cellulose acetate (CA)/acetone/water casting solutions. The KC-135 aircraft provides the capability for greatly reducing the effective gravitational body forces that influence the buoyancy force on MVs. Buoyancy should have no effect on MV growth as proposed in the purely diffusive growth hypothesis but should influence MV growth via the solutocapillary convection hypothesis since the latter involves a balance between Marangoni, viscous drag, and buoyancy forces. CA membranes were cast in low-gravity (low-g) (KC-135) and normal-gravity (1-g) (ground-based control) from CA/acetone/water solutions as a function of the solvent/non-solvent (S/NS) ratio. Morphological analysis indicated that MV growth was enhanced in low-g only for the case in which the S/NS ratio=2.0; no effect was observed for higher values of the S/NS ratio. These studies provide support for the solutocapillary convection hypothesis; however, the present data do not unambiguously demonstrate the occurrence of solutocapillary convection. Further research is required to provide such proof. [Copyright &y& Elsevier]

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. • A serial configuration is used to determine the true permeation resistance of the porous support under RO condition. • The plastic strain of the porous support under the serial configuration is determined. • The porous support experience significantly more deformation under RO condition than under direct permeation measurements. • True resistance of the porous support is significant for a TFC membrane under high-pressure RO. [ABSTRACT FROM AUTHOR]

Molecular layer deposition (MLD) is a gas-phase deposition technique that can create ultra-thin films with precisely controlled chemical composition and thickness by depositing one monolayer at a time. This makes MLD an attractive technology for desalination membranes among other applications. Given its relatively recent development, little information has been reported regarding the properties of MLD thin films. We present the results of an initial mechanical property study of MLD films with thicknesses ranging from ∼50 to 2000 nm. MLD was utilized to create crosslinked polyamide films grown using either m -phenylenediamine (MPD) and trimesoyl chloride (TMC) reactants or piperazine (PIP) and TMC reactants. The elastic modulus of the films was determined using atomic force microscopy (AFM). The results show that the modulus was independent of film thickness with values of 4.36 ± 1.19 GPa and 5.24 ± 1.06 GPa for the MLD films grown using the MPD-TMC and PIP-TMC chemistries, respectively. These values are of the same order of magnitude as those reported for much thicker polyamide films, but higher than the modulus of polyamide films fabricated using interfacial polymerization. [Display omitted] • All-organic polyamide thin films were fabricated using molecular layer deposition. • The elastic modulus of the films was measured using atomic force microscopy. • Two film chemistries with thicknesses between ∼50 and 2000 nm were evaluated. • Modulus was independent of chemistry and film thickness. • Modulus values of ∼3–6 GPa were similar to those of bulk polyamides. [ABSTRACT FROM AUTHOR]

This study directly compares the mechanical behavior of novel molecular layer deposition (MLD) and analogous interfacial polymerization (IP) polyamide thin films in environments relevant to reverse osmosis (RO) membrane operation. The elastic modulus of the films was determined using atomic force microscopy (AFM) in dry, hydrated, and chlorinated states. Surface roughness characteristics were also obtained given their potential influence on AFM modulus measurements. The much smoother MLD films demonstrated a statistically higher modulus in all states as compared to their IP counterparts. The MLD films maintained a modulus ∼3X and ∼5X greater than that of IP films after hydration and chlorination, respectively. Such differences in behavior may be due to the higher density and correspondingly lower void content of the MLD films. Results from this study provide a rationale for future development of MLD for fabrication of polyamide films for incorporation in RO membranes. [Display omitted] • Novel polyamide thin films were fabricated by molecular layer deposition (MLD). • Physical and mechanical characteristics of MLD films were compared to interfacially polymerized (IP) films of similar thickness. • Elastic modulus and RMS roughness were measured using atomic force microscopy. • Modulus was measured in dry, hydrated, and chlorinated conditions. • MLD films were much smoother and had a statistically greater modulus as compared to IP films in all conditions. [ABSTRACT FROM AUTHOR]

Abstract: Flux decline due to membrane fouling prevails in almost all pressure-driven liquid separations. The factors controlling fouling, ranging from surface chemistry to topographic roughness, have been extensively investigated. However, the role of surface patterns, particularly at a submicron scale, on membrane fouling remains unclear. Herein, we demonstrate that submicron patterns can be successfully imprinted onto a commercial polysulfone ultrafiltration membrane surface using nanoimprint lithography (NIL) without sacrificing its permeability properties. The presence of these patterns led to significantly improved deposition resistance during filtration of colloidal silica particle suspensions, as evidenced by a 19–45% increase in the apparent critical flux, with the magnitude dependent on particle size. Post-filtration visualization reveals an intriguing anisotropy in the particle deposition, whereby the degree of anisotropy depends on the orientation angle between the surface pattern and the flow direction of the feed. These results suggest a chemical-free route to post-formation, membrane surface modification. [Copyright &y& Elsevier]

Abstract: Potable water for municipal and agricultural use is produced in many regions of the world by membrane-based desalination processes. Brackish water is driven by a pump through pressurized modules where the water passes through a semi-permeable membrane, while rejected salt ions are retained. During pressure-driven desalination, the rejected salt ions accumulate by convective mass transport near the membrane surface, resulting in elevated concentration levels. Concentration polarization (CP) of the dissolved salts can lead to precipitation and crystal growth on the membrane, known as scaling. Over time, scaling can decrease process efficiency because water can no longer permeate through the affected areas. Scalant removal can incur significant chemical costs, result in system downtime, and reduce membrane lifetime. Several techniques have been reported in the literature for real-time monitoring of scaling, but little work has been conducted on real-time characterization of the concentration polarization that leads to scaling. This work describes an electrolytic sensor system that can be used in monitoring solute concentration within the thin concentration polarization boundary layer (CPBL) that forms near the membrane surface. All experiments were performed in a bench-scale flat-sheet cross-flow system using aqueous calcium sulfate feed solutions. This design has improved upon previously reported work by applying a more robust sensor system in a challenging flow-channel environment that more closely resembles industrial desalination units. [Copyright &y& Elsevier]

Abstract: Thin film composite (TFC) reverse osmosis (RO) membranes enjoy widespread use in desalination, but their sensitivity to oxidizing agents such as chlorine remains a continuing challenge. In contrast to many reports on the chemical aspects associated with decreased membrane performance after chlorine exposure, studies on the fundamental physical properties of the polyamide barrier layer (PBL) of TFC membranes are scarce. This omission is mostly due to the lack of techniques capable of characterizing such interfacially polymerized PBLs, which are ultrathin and insoluble. The focus of this study is the development of an AFM-based nano-thermal analysis technique that provides the first-ever result for the direct measurement of the glass transition temperature (Tg ) of the PBL on several commercial TFC RO membranes. Moreover, the technique is utilized to study the changes in Tg of the PBL after exposure to chlorine solutions as a function of concentration and duration at constant pH. Results indicate significant and systematic reduction in Tg of the PBL with increasing chlorine concentration and exposure time. [Copyright &y& Elsevier]

Permeability of a porous material with a fluid interface is shown to be related to the propagation of the slow longitudinal wave. The propagation threshold of the slow longitudinal wave occurs when the wave number is higher than the critical wave number, kcr. Measuring kcr can provide the intrinsic permeability of a porous interface. The ability to detect a change in kcr due to differences in pore size and fluid viscosity is demonstrated. This measurement is demonstrated in a model material with two pore sizes and two fluid viscosities. The results suggest opportunities to extend the method to a range of materials of scientific and technical importance. [ABSTRACT FROM AUTHOR]

Standard melting point analyses only partially describe the thermal properties of eusocial beeswaxes. Differential scanning calorimetry (DSC) revealed that thermal phase changes in wax are initiated at substantially lower temperatures than visually observed melting points. Instead of a sharp, single endothermic peak at the published melting point of 64"C, DSC analysis of Apis mellifera Linnaeus wax yielded a broad melting curve that showed the initiation of melting at approximately 40&x#00B0;C. Although Apis beeswax retained a solid appearance at these temperatures, heat absorption and initiation of melting could affect the structural characteristics of the wax. Additionally, a more complete characterization of the thermal properties indicated that the onset of melting, melting range and heat of fusion of beeswaxes varied significantly among tribes of social bees (Bombini, Meliponini, Apini). Compared with other waxes examined, the relatively malleable wax of bumblebees (Bombini) had the lowest onset of melting and lowest heat of fusion but an intermediate melting temperature range. Stingless bee (Meliponini) wax was intermediate between bumblebee and honeybee wax (Apini) in heat of fusion, but had the highest onset of melting and the narrowest melting temperature range. The broad melting temperature range and high heat of fusion in the Apini may be associated with the use of wax comb as a free-hanging structural material, while the Bombini and Meliponini support their wax structures with exogenous materials. [ABSTRACT FROM AUTHOR]

Extra-cellular polysaccharides (EPS), soluble microbiological products (SMP), dispersed bacterial cells, and a well-characterized natural organic matter (NOM) isolate were observed to determine their influence on the flux decline of model nanofiltration membrane systems. Biofouling tests were conducted using bench-scale, flat-sheet membrane modules, fed with particle-free (laboratory) waters and natural waters, some of which were augmented with readily biodegradable organic carbon. The modules were operated 6.7 × 105 Pa, and 21 ± 2° C. Membrane flux-decline was associated with increases in surface EPS mass: between 30 and 80% of normalized flux decline occurred when membrane-associated EPS content increased from 5to 50 μg/ cm². As judged by standard culturing, heterotrophic cell densities recovered from membrane biofilm samples showed no significant correlations with the different carbon sources present in the feedwaters, or flux decline rates. Results suggested that, in the absence of microbiological activity, SMP and NOM have intrinsic membrane fouling properties at levels that are operationally significant to commercial-scale membrane treatment practices. Results also suggested that SMP may have a biofouling potential significantly greater than some types of NOM. Trends obtained relating these compounds with flux decline were successfully described by expanding existing resistance-in-series models. [ABSTRACT FROM AUTHOR]

Beeswax is a multicomponent material used by bees in the genus Apis to house larvae and store honey and pollen. We characterized the mechanical properties of waxes from four honeybee species: Apis mellifera L., Apis andreniformis L., Apis dorsata L. and two subspecies of Apis cerana L. In order to isolate the material effects from the architectural properties of nest comb, we formed raw wax in to right, circular cylindrical samples, and compressed them in an electromechanical tensometer. From the resulting stress-strain curves, values for yield stress, yield strain, stress and strain at the proportional limit, stiffness, and resilience were obtained. Apis dorsata wax was stiffer and had a higher yield stress and stress at the proportional limit than all of the other waxes. The waxes of A. cerana and A. mellifera had intermediate strength and stiffness, and A. andreniforinis wax was the least strong, stiff and resilient. All of the waxes had similar strain values at the proportional limit and yield point. The observed differences in wax mechanical properties correlate with the nesting ecology of these species. A. mellifera and A. cerana nest in cavities that protect the nest from environmental stresses, whereas the species with the strongest and stiffest wax, A. dorsata, constructs relatively heavy nests attached to branches of tall trees, exposing them to substantially greater mechanical forces. The wax of A. andreniformis was the least strong, stiff and resilient, and their nests have low masses relative to other species in the genus and, although not built in cavities, are constructed on lower, often shielded branches that can absorb the forces of wind and rain. [ABSTRACT FROM AUTHOR]

Abstract: In membrane separation processes, the presence of the concentration polarization boundary layer (CPBL) often leads to a decline in the permeate flux and an increased risk of membrane fouling. Although the study of membrane fouling has benefited from the recent development of real-time, non-invasive acoustic measurements of the fouling process under realistic conditions, measurement of concentration polarization is still difficult and rather limited. This paper describes the development of interdigitated capacitive microsensors for real-time in-situ monitoring of CPBL growth in a cross-flow nanofiltration membrane module using calcium sulfate (CaSO4) solution as the feed. The developed capacitive sensors respond to changes in solute concentration as a function of distance from the membrane surface. Detection capability was determined in a series of comprehensive experiments with systematic changes in feed concentration and module operating parameters including upstream pressure, flow rate, and feed composition. The specially designed microscale capacitor assembly provides a unique capability for real-time characterization of the transient and steady-state concentration boundary layer polarization behavior. The capacitive microsensor concentration polarization measurements were corroborated via independent membrane morphological analysis and standard performance metrics. The experimental data were in excellent qualitative agreement with theoretical predictions from a mathematical model of concentration polarization behavior. In addition, the use of microcapacitor sensors in combination with ultrasonic time-domain reflectometry, enabled real-time observation of the development of scaling from the initiation of concentration polarization through the onset of membrane fouling. These results clearly demonstrate the advantages of a multisensor approach to the measurement of membrane phenomena, and provide a basis for the development of “smart” membranes. [Copyright &y& Elsevier]

Abstract: The major objective of this study was to develop a mathematical model that describes the solid–liquid (S/L) thermally induced phase separation (TIPS) membrane-formation process and captures the fundamental features of the evolving structure. This is the first mathematical model to describe S/L TIPS process from the initiation of casting to the development of the final membrane structure. The model predictions were validated with experimental measurements for the isotactic polypropylene/dotriacontane system using both scanning electron and optical microscopy to determine the final spherulitic size. These experiments encompassed two different process (boundary) conditions: controlled cooling rate and constant cooling-block temperature. The final spherulite diameter was in statistical agreement with the model predictions for the controlled cooling rate condition and the constant cooling-block temperature condition when the latter was equal to or higher than 25°C. The predicted spherulite diameter was larger than observed for lower block temperatures most likely due to diluent solidification, which was not accounted for in the model. This model can be used to determine the operating conditions required to produce desired membrane morphologies in the S/L TIPS process. Moreover, the formalism used to incorporate nucleation and growth of the dispersed phase in this model can be extended to other phase-inversion processes utilized for membrane manufacture. [Copyright &y& Elsevier]

Chemical characterization of scaling and removal processes was performed in real time via Raman spectroscopy in a bench-scale reverse osmosis (RO) system. A custom RO cross-flow cell was integrated with a Raman microscope objective, allowing for analysis of localized membrane scaling and scale removal. Permeate flux was also measured to provide a real-time metric for comparison. A commercial flat sheet, thin-film composite reverse osmosis (TFC RO) membrane was scaled using a calcium sulfate (CaSO 4 ·H 2 O) feed solution. Upon CaSO 4 scale detection, the feed was switched to DI water, which served as a cleaning agent to remove the CaSO 4 scale from the membrane. In addition to the real-time local (Raman) and global (permeate flux) measurements, membrane samples were characterized post-mortem using Raman spectroscopy, gravimetric analysis and scanning electron microscopy to provide important scaling and scale removal metrics. Results from real-time measurements indicated that changes in Raman intensity were a more sensitive indicator of local scale removal than changes in permeate flux, a standard cleaning performance metric; these findings were corroborated by the post-mortem analyses. Overall, the membrane cleaning experiments showed that Raman spectroscopy provided crucial real-time chemical composition and spatial distribution information, which can inform more effective antiscaling and cleaning strategies. Unlabelled Image • Raman spectroscopy provides real-time chemical analysis of localized RO membrane scaling and scale removal. • Real-time Raman results compared with permeate flux changes as well as multiple post-mortem metrics. • Raman spectroscopy with optimized sampling area could support improved anti-scaling and cleaning strategies. [ABSTRACT FROM AUTHOR]

Early-stage scaling detection is a crucial component for optimizing proactive anti-fouling measures that enhance membrane lifetime and decrease operation costs. In this work, we utilize Raman spectroscopy to detect and chemically quantify multiple scalants during bench-scale reverse osmosis desalination. The experiments were conducted with a commercial brackish water thin-film composite membrane at a feed pressure of 1.2 MPa (175 psi) and a feed flow velocity of 4.2 cm/s. Raman measurements were performed in real-time at a laser excitation wavelength of 785 nm. Experimental results from single-feed solutions of CaSO 4 and CaCO 3 show consistent detection of the corresponding scalants with less than a 15% permeate flux decrease at detection inclusive of the permeate decline due to compaction. Experiments utilizing a mixed-feed solution containing CaSO 4 and CaCO 3 were also conducted. Results for the mixed-feed experiments showed detection of CaSO 4 scaling only. Subsequent analysis indicated that a modified sampling strategy was required for successful real-time detection of both CaSO 4 and CaCO 3 scaling. • Real-time early-stage scaling detection via Raman spectroscopy. • Local scaling detection with chemical identification. • Demonstration of sensitive scaling detection in CaSO 4 and CaCO 3 feeds. • Modified sampling strategy for multiple scalant detection in mixed feed solutions. [ABSTRACT FROM AUTHOR]

In-situ monitoring techniques of reverse osmosis (RO) desalination systems, particularly those with chemical sensing capabilities, can provide the means for better understanding important scaling mechanisms as well as early scaling detection. In this work, both calcium sulfate and calcium carbonate scaling on RO membranes were detected concurrently in real time using Raman spectroscopy to provide a unique chemical fingerprint. Two different sampling methodologies (manual and automated) were employed, and their performance was evaluated by comparing the Raman detection times to concurrent values of flux decline. The manual sampling strategy resulted in the detection of calcium sulfate and calcium carbonate at mean permeate flux declines of 13 ± 10 % and 22 ± 3 %, respectively. The automated sampling strategy provided better performance, with detection of calcium sulfate and calcium carbonate at mean flux declines of 8 ± 5 % and 4 ± 3 %, respectively. The increased sensitivity and decreased variability of the automated sampling strategy provided valuable preliminary insights for the selection of optimized sampling strategies. The ability to identify the chemical composition of different scaling crystals including their polymorphs is an important step toward better understanding of the crystallization pathways of multi-component feed streams used in seawater and brackish water RO desalination. [Display omitted] • Real-time, concurrent detection of gypsum and calcite scaling using Raman spectroscopy • Raman results confirmed by post-mortem SEM analysis and gravimetric measurements • Improved detection results obtained using an automated sampling methodology • Early Raman detection of mixed-salt scaling achieved at low values of flux decline [ABSTRACT FROM AUTHOR]

Abstract It is commonly believed that the overall permeation resistance of thin film composite (TFC) membranes is dictated by the crosslinked, ultrathin polyamide barrier layer, while the porous support merely serves as the mechanical support. Although this assumption might be the case under low transmembrane pressure, it becomes questionable under high transmembrane pressure. A highly porous support normally yields under a pressure of a few MPa, which can result in a significant level of compressive strain that may significantly increase the resistance to permeation. However, quantifying the influence of porous support deformation on the overall resistance of the TFC membrane is challenging. In particular, it is difficult to determine the deformation/strain of the membrane during active separation. In this study, we use nanoimprint lithography (NIL) to achieve precise compressive deformation in commercial TFC membranes. By adjusting the NIL conditions, membranes were compressed to strain levels up to 60%. SEM and AFM measurements showed that the compression had minimal impact on the barrier-layer surface morphology and total surface area with most of the deformation occurring in the support layer. DI water permeation measurements revealed that the water flux reduction decreases with an increase of strain level. Most significantly, the intrinsic membrane resistance showed negligible changes at strain levels lower than 30%–40%, but increased exponentially at higher strain levels, reaching 250%–500% of pristine (unstrained) membrane values. Using a resistance-in-series model, the strain dependency of the TFC membrane resistance can be described. Highlights • Different levels of compressive strain were imposed on TFC membranes using Nanoimprint Lithography. • The intrinsic membrane resistance of the compressed TFC membranes was determined. • The intrinsic membrane resistance increases significantly when compressive strain in the support layer is above 40%. • The influence of support layer deformation on the TFC membrane resistance can be described using a resistance-in-series model. [ABSTRACT FROM AUTHOR]

Surface roughness of membranes is often perceived by many as a factor that promotes fouling during filtration, and thus is undesirable. Almost all liquid-based separation membranes display flat surfaces with an intrinsic surface roughness that is associated with the membrane manufacturing process. Recently, polymer ultrafiltration and thin film composite membranes containing regular, periodic surface patterns were fabricated using cost-effective lithographic methods. Here, we review the work to date on the fabrication and characterization of these patterned membranes with a focus on processing–structure–performance relationships. In addition, the antifouling performance of these membranes against model foulants including colloidal suspensions and protein solutions is also highlighted. [ABSTRACT FROM AUTHOR]

Imparting sub-micron periodic patterns on the surface of ultrafiltration (UF) membranes has been shown to improve their antifouling characteristics. However, the deformation mechanism underlying membrane surface-patterning with nanoimprint lithography (NIL) is currently unclear. In response to this need, this study addresses the influence of nanoimprinting on the structural and performance characteristics of a commercial polyethersulfone (PES) UF membrane. The work utilized a flat (no pattern) as well as a pattern-containing mold such that local surface deformation associated with pattern formation could be isolated from the overall mechanical deformation in compression. The mechanical properties of the UF membrane as a function of temperature and deformation rate were characterized, and the overall thickness, molecular weight cutoff, and DI water permeance were measured for membranes imprinted using the flat mold. The data show that the influence of the NIL process on the membrane structure is length-scale dependent. Furthermore, imprinting of the UF membrane with the pattern-containing mold was examined experimentally as well as with finite element simulation. Results indicate that the non-uniform contact deformation at the membrane–mold interface provides the potential to optimize the NIL conditions for achieving desired pattern geometries without significantly increasing the membrane resistance. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the effects of sub-micron surface patterns on the fouling of a model protein solution (bovine serum albumin (BSA)), was investigated during active filtration and simple adsorption conditions. Surface patterns were created directly onto a commercial polyethersulfone ultrafiltration membrane using nanoimprint lithography, which resulted in a moderately reduced molecular mass cut-off (MWCO) but similar permeance as its non-imprinted counterpart as well as significantly improved resistance to BSA fouling. Staged filtration experiments, with backwash cleaning, revealed that the permeate flux of the imprinted membrane was considerably higher than that of the non-imprinted membrane, consistent with UV–vis measurements showing less protein deposition on the imprinted membranes. This improvement in anti-fouling characteristics for the imprinted membrane was universally observed for varying feed-solution chemistry including changes in both pH and ionic strength. From controlled protein-adsorption experiments under non-filtration conditions, it appears that the observed decrease in protein adsorption on the imprinted membranes is likely associated with altered hydrodynamics due to the presence of the sub-micron patterns. [Copyright &y& Elsevier]

Abstract: Reverse osmosis (RO) desalination is a well-established process that removes salt from sea water or brackish water sources. However, scaling by sparingly soluble salts on the membrane surface has been shown to significantly degrade membrane performance. We report the results from a comprehensive study evaluating the effectiveness of flow reversal (FR) controlled by ultrasonic sensors in mitigating scaling during RO desalination. The work utilized a sophisticated multi-port bench-scale flat-sheet cross-flow module with the ability to operate in FR mode with externally mounted ultrasonic sensors. A novel signal-analysis methodology was developed to utilize the ultrasonic waveforms to control a switch in flow direction at the onset of local scaling. Experiments were conducted under controlled conditions with repeated forward-flow (FF) and reverse-flow (RF) cycles. Data from the experiments confirmed that FR controlled by ultrasonic sensors can effectively mitigate scaling on the membrane surface and avoid the expected level of permeate-flow decrease. These results were validated by post-mortem membrane analysis including scalant gravimetric and membrane area-coverage measurements. Overall, the work demonstrates the successful adaptation of ultrasonic sensors for active process control in which the timing of the change in flow direction is critical. [Copyright &y& Elsevier]

Abstract: The use of ultrasonic time-domain reflectometry (UTDR) in combination with statistically based analysis has been utilized to provide timely warning of the initial onset of local calcium carbonate scaling. The methodology was able to detect the onset of scaling in real time before any significant decrease in permeate flux was observed. Ultrasonic detection of scaling was confirmed via post-mortem examination of the membrane that showed the presence of aragonite crystals that were as small as 20μm and covered less than 10% of the membrane surface. The ultrasonic methodology was then employed to trigger a change in flow direction (reversal of the concentrate and feed ends of the flow channel) when scaling was detected. When in forward flow, the upstream, midstream and downstream sections of the membranes had aragonite supersaturation values of SI∼2.0, ∼5.3 and∼7.65, respectively; when the flow direction was changed, the SI values at the ends were switched but the SI at the midstream remained at SI∼5.3. Results indicated that flow reversal effectively mitigated scaling in downstream sections of the membrane even though they were periodically exposed to the highest supersaturation conditions. It was demonstrated that prompt intervention after an ultrasonic scaling signal improved the efficacy of flow reversal. The results reflect a significant advance in the use of UTDR in which the methodology is applied for active control of scaling miti ation rather than limited to passive detection of scale formation. [Copyright &y& Elsevier]

Abstract: In this study we report changes in the glass transition temperature (T g ) of the polyamide barrier layer (PBL) of a commercial RO membrane as a function of chlorine treatment in which concentration and pH were systematically varied. The results indicate a monotonic decrease of T g with increasing exposure time at a given chlorine concentration. Further, both the degree and the rate of T g decrease vary significantly with both the chlorine concentration and pH value of the aqueous chlorine solution. Moreover, the decrease in PBL T g correlates well with the reduction in the salt rejection of the membrane, but the magnitude of the correlation is specific to chlorine concentration and pH values. [Copyright &y& Elsevier]

Abstract: Nanofiltration (NF) membranes have found more frequent use in recent years for the desalination of seawater and other sources of brackish water because they can be used at lower pressures than more traditional reverse-osmosis (RO) technologies, and thus provide overall energy savings. However, membrane fouling still presents a common and significant challenge in practical applications. Currently, the performance of membrane-based liquid separation processes is most often monitored by external, volumetric flow-based techniques that provide delayed information on fouling layer development. The delay between initial growth and the observation of fully established fouling reduces the efficacy of cleaning and remediation measures. The focus of this study is the use of ultrasonic time–domain reflectometry (UTDR) as a non-destructive method for real-time, in-situ monitoring of early-stage inorganic scaling layer formation on NF membranes. This work utilizes miniature-scale ultrasonic transducers that are internally integrated into a flat-sheet cross-flow filtration module and in contact with the membrane. Comparisons are made with results obtained from externally mounted UTDR transducers, a more commonly used arrangement. Results show that while the internal sensors can be somewhat more sensitive, the significance of this improvement can be negated by scaling deposition that is hindered by the presence of the sensor. [Copyright &y& Elsevier]

Abstract: Poly(ethylene chlorotrifluoroethylene) (ECTFE) is a 1:1 alternating copolymer of ethylene and chlorotrifluoroethylene that offers excellent resistance in chemically and thermally challenging environments. ECTFE membranes with a variety of microstructures have been fabricated via thermally induced phase separation (TIPS) with dibutyl phthalate (DBP) as the diluent. A continuous flat sheet extrusion apparatus with a double rotating drum was used that permitted controlling both the casting solution thickness and axial tension on the nascent membrane. Initial compositions of ECTFE/DBP solutions in the liquid–liquid region of the binary phase diagram were chosen, resulting in membranes with an interconnected pore structure. The effects of several important process parameters were studied to determine their effect on the structure and properties of the membrane. The parameters evaluated included the initial ECTFE concentration, cooling rate, membrane thickness, co-extrusion of diluent, and stretching of the nascent membrane. The resulting membranes were characterized using SEM, porometry, and permeation measurements. For the range of process parameters studied, ECTFE membranes exhibited a decrease in surface porosity with increasing initial polymer concentration and cooling rate. The effect of membrane thickness on the permeation flux was not significant. Co-extrusion of diluent increased the surface porosity and eliminated the dense skin that was otherwise present under rapid cooling conditions. Subsequent stretching of the nascent membrane resulted in a more open structure and a significant increase in the permeation flux. [ABSTRACT FROM AUTHOR]

Abstract: Driven by the concerns over the dwindling supplies of petroleum and the dire consequences of global warming, the emergence of a hydrogen economy appears inevitable. Such development will require the advancement of separation technologies with significantly improved energy and cost efficiencies. Membrane technology is the ideal choice for hydrogen purification due to its lower power usage and costs, simplicity in operation, as well as compactness and portability. Assuming hydrogen purity requirements of <99.5% and relatively modest operating temperatures, polymeric membranes are preferred among the various alternatives. Generally, polymeric membranes for hydrogen enrichment are either H2- or CO2-selective, depending on the governing kinetic or thermodynamic factors. In this review, the current state-of-the-art for polymeric membranes applicable to hydrogen purification is considered, and the different approaches for enhancing intrinsic gas-separation performance are evaluated. An assessment of the benefits and shortcomings of the respective membrane types are presented, and the future directions most promising for the development of robust and high-performance polymeric membranes for the hydrogen economy are highlighted. [Copyright &y& Elsevier]

Abstract: A novel protocol is developed to characterize nanofiltration (NF) and reverse osmosis (RO) membranes that employ the Spiegler–Kedem membrane-transport model based on irreversible thermodynamics coupled with a Film Theory description of the concentration polarization. The novel aspect of this characterization protocol is extracting the concentration polarization boundary-layer thickness as well the three membrane transport parameters from permeation data. This methodology is applied to four dilute aqueous salt systems for a Dow Filmtech NF-255 membrane and one dilute aqueous salt system for a Dow Filmtech BS-30 membrane that were studied using a wellmixed flat sheet membrane permeation cell. Interestingly, the total volumetric flux and intrinsic rejection can be described quite well over the entire range of studied feed concentration, flow rates, and transmembrane pressures using constant membrane transport coefficients in the Spiegler–Kedem model. However, it should be emphasized that the conclusions drawn from this study are restricted to the dilute aqueous salt solutions that were employed. Some prior studies of aqueous salt systems have found it necessary to employ concentration-dependent transport coefficients to describe the permeation behavior. It is possible that the more exacting method for determining the thickness of the concentration boundary-layer thickness that is used in this study properly accounts for volumetric flow rate effects that have been attributed to nonconstant membrane transport coefficients. A design correlation for the intrinsic rejection of an NF or RO membrane as a function of the total volumetric flux is developed that encompasses the full range of concentrations used in the experiments, flow rates, and transmembrane pressures for a specified binary aqueous salt system. This design correlation formalism in principle can be used to characterize any NF or RO membrane irrespective of the type of membrane contactor employed. [Copyright &y& Elsevier]

Abstract: Biofilm growth on polymeric surfaces was monitored using ultrasonic frequency-domain reflectometry (UFDR). The materials utilized for this study included nonporous polycarbonate (PC) sheets, polyamide (PA) nanofiltration composite membranes and porous polyvinylidene fluoride (PVDF) microfiltration membranes (nominal pore size: 0.65 μm). Coupons of each material were placed in a biologically active annular reactor for up to 300 days, and subjected to a constant shear field (0.12 N m−2), which induced sessile microbial growth from acetate amended municipal tap water. Acoustic monitoring was non-destructively executed by traversing coupons in a constant temperature water bath using a spherically focused 20- MHz immersion transducer. This semi-automated system was configured to obtain reflections from 50 regions (c.a. 120×103 μm2) distributed evenly near the centerline of each coupon. The resulting reflected power distributions were compared with standard biochemical and microscopic assays that described surface associated biofilms. When compared to clean (virgin) conditions, biofilms growing on coupons induced consistent attenuations in reflection amplitude, which caused statistically significant shifts in reflected power (p <0.01). Using exocellular polysaccharides as a surrogate measure of total biofilm mass, UFDR was able to detect biofilms developing on any of the materials tested at surface-averaged masses ≤150 μg cm−2. Above these threshold levels, increasing amounts of exocellular polysaccharides correlated with significant decreases in total reflected power (TRP). The distribution of biomass on the coupon surfaces determined by acoustic spectra was consistent with that observed using environmental scanning electron microscopy (ESEM). These results suggest that UFDR may be used as a non-destructive tool to monitor biofouling in a wide variety of applications. [Copyright &y& Elsevier]

Abstract: Shape memory polymers (SMPs) can retain a temporary shape after pre-deformation at an elevated temperature and subsequent cooling to a lower temperature. When reheated, the original shape can be recovered. Relatively little work in the literature has addressed the constitutive modeling of the unique thermomechanical coupling in SMPs. Constitutive models are critical for predicting the deformation and recovery of SMPs under a range of different constraints. In this study, the thermomechanics of shape storage and recovery of an epoxy resin is systematically investigated for small strains (within ±10%) in uniaxial tension and uniaxial compression. After initial pre-deformation at a high temperature, the strain is held constant for shape storage while the stress evolution is monitored. Three cases of heated recovery are selected: unconstrained free strain recovery, stress recovery under full constraint at the pre-deformation strain level (no low temperature unloading), and stress recovery under full constraint at a strain level fixed at a low temperature (low temperature unloading). The free strain recovery results indicate that the polymer can fully recover the original shape when reheated above its glass transition temperature (T g). Due to the high stiffness in the glassy state (T < T g), the evolution of the stress under strain constraint is strongly influenced by thermal expansion of the polymer. The relationship between the final recoverable stress and strain is governed by the stress–strain response of the polymer above T g. Based on the experimental results and the molecular mechanism of shape memory, a three-dimensional small-strain internal state variable constitutive model is developed. The model quantifies the storage and release of the entropic deformation during thermomechanical processes. The fraction of the material freezing a temporary entropy state is a function of temperature, which can be determined by fitting the free strain recovery response. A free energy function for the model is formulated and thermodynamic consistency is ensured. The model can predict the stress evolution of the uniaxial experimental results. The model captures differences in the tensile and compressive recovery responses caused by thermal expansion. The model is used to explore strain and stress recovery responses under various flexible external constraints that would be encountered in applications of SMPs. [Copyright &y& Elsevier]

Video-microscopy flow-visualization (VMFV) is adapted to study the development of macrovoid (MV) pores in the dry-casting of cellulose acetate (CA)/acetone/water solutions. Particle tracer velocities provide the first direct evidence for the presence of solutocapillary-driven convection that can enhance mass-transfer to a MV. Three phases of MV development are observed: fast initial growth, slow growth, and collapse. During the latter, MVs were observed on occasion to initiate far from the demixing front. These studies have led to a significantly modified hypothesis for MV development. Extremely rapid initial MV growth is thought to occur owing to coalescence of dispersed phase microdroplets. To ensure net mass-transfer to a growing MV, it is postulated that a homogeneous supersaturated solution layer must exist between the demixed fluid layer and the homogeneous stable solution layer. Fast growth also involves convective mass-transfer to the MV whose surface is initially entirely immersed in this homogeneous supersaturated solution layer. Slow growth involves net transport that results from both convective mass-transfer to the MV across the portion of its surface in contact with the homogeneous supersaturated solution layer, and convective mass-transfer from the portion of its surface that extends into the homogeneous stable solution layer. Active collapse is thought to occur owing to skin formation at the MV surface. Passive collapse occurs when the convective mass-transfer from the MV in the homogeneous stable solution layer exceeds that entering the MV in the homogeneous supersaturated solution layer. [Copyright &y& Elsevier]

The recent advancement of semiconductor devices to the near-atomic scale necessitated the development of atomic layer processing methods, including molecular layer deposition (MLD). This gas-phase deposition technique creates semipermeable polymer films with precise control of composition and thickness. Herein, MLD was used to produce thin-film composite reverse osmosis membranes. Aromatic polyamide films as thin as 0.5 nm were applied to NF270 nanofiltration membranes using m -phenylenediamine and trimesoyl chloride. Within two molecular layers, desalination performance was affected. As film thickness increased to 15 nm (48 MLD cycles), performance progressed from nanofiltration to reverse osmosis metrics in terms of salt rejection and water permeance. With film thickness > 5 nm, rejection values exceeded a small sampling of commercial membranes. In all cases, a tradeoff between rejection and permeance was observed. Atomic force microscopy measurements indicate that MLD enhancement led to removal of small-scale roughness features and resulted in a root mean square roughness difference of <0.1 nm from the substrate. These initial MLD studies represent a novel processing approach that offers a potential pathway for the fabrication of membranes with finely tailored properties. [Display omitted] • MLD added an ultrathin MPD-TMC polyamide active layer to commercial NF membranes. • Progressive MLD systematically altered flux/rejection metrics from NF to RO values. • Controlled increase of MLD layer thickness increased rejection but decreased flux. • Atomic force microscopy revealed that MLD removed small-scale roughness features. [ABSTRACT FROM AUTHOR]

The recent advancement of semiconductor devices to the near-atomic scale necessitated the development of atomic layer processing methods, including molecular layer deposition (MLD). This gas-phase deposition technique creates semipermeable polymer films with precise control of composition and thickness. Herein, MLD was used to produce thin-film composite reverse osmosis membranes. Aromatic polyamide films as thin as 0.5 nm were applied to NF270 nanofiltration membranes using m -phenylenediamine and trimesoyl chloride. Within two molecular layers, desalination performance was affected. As film thickness increased to 15 nm (48 MLD cycles), performance progressed from nanofiltration to reverse osmosis metrics in terms of salt rejection and water permeance. With film thickness > 5 nm, rejection values exceeded a small sampling of commercial membranes. In all cases, a tradeoff between rejection and permeance was observed. Atomic force microscopy measurements indicate that MLD enhancement led to removal of small-scale roughness features and resulted in a root mean square roughness difference of <0.1 nm from the substrate. These initial MLD studies represent a novel processing approach that offers a potential pathway for the fabrication of membranes with finely tailored properties. [Display omitted] • MLD added an ultrathin MPD-TMC polyamide active layer to commercial NF membranes. • Progressive MLD systematically altered flux/rejection metrics from NF to RO values. • Controlled increase of MLD layer thickness increased rejection but decreased flux. • Atomic force microscopy revealed that MLD removed small-scale roughness features. [ABSTRACT FROM AUTHOR]