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Ultrapure water production is vital for sustainable green hydrogen production by electrolysis. The current industrial process to generate ultrapure water involves energy-intensive processes, such as reverse osmosis. This study demonstrates a facile method to produce ultrapure water from simulated seawater using a low capital cost and low-energy-consuming membrane distillation (MD) approach that is driven by the waste heat from photovoltaic (PV) panels. To optimize the PV-MD operation, modeling efforts to design a multilayered MD system were carried out. The results were used to guide the construction of several prototype devices using different materials. The best performing PV-MD device, containing evaporation and condensation regions made from steel sheets and polytetrafluoroethylene (PTFE) membranes, can produce high-purity water with conductivity less than 40 mS and flux higher than 100 g/m2 h, which is suitable for typical electrolyzer use. [ABSTRACT FROM AUTHOR]

Thin-film nanofibrous composite (TFNC) membranes, containing a multi-layered structure, for nanofiltration (NF) were demonstrated. The best performing membranes consisted of a three-layered structure, including the poly(ethylene terephthalate) (PET) non-woven support, polyacrylonitrile (PAN) electrospun mid-layer, and composite barrier layer based on cellulose nanofibers (CN) and polyamide (PA) matrix made by interfacial polymerization. Under the chosen test conditions (482 kPa, 2000 ppm MgSO 4 as the feed solution), all manually coated TFNC-NF membranes exhibited high rejections (above 99%), where the best membrane showed a flux of 44.7 L/m 2 h (LMH), significantly higher than that of the membrane prepared by the conventional phase-inversion substrate (its flux was 27.6 LMH). Transmission electron microscopy (TEM) indicated that the CN component embedded in the PA matrix probably introduced directed water channels, thus increasing the permeability of the barrier layer. The machine-driven slot-die coating method was applied to improve the membrane performance by reducing the barrier layer thickness through regulating the organic solution delivery in interfacial polymerization. With the optimized organic solution delivery, the membranes exhibited a flux of 71.7 LMH and a rejection of 98.5%, which were better than those of a commercial NF membrane (DOW Filmtec NF 270) having similar barrier layer chemical compositions. The flux of the slot-die coated TFNC-NF membrane was further improved by using 20 wt% bipiperidine (BP) with respect to the total amine monomers for interfacial polymerization, where the membrane exhibited a flux of 94.3 LMH (i.e., doubling the flux of NF 270) and a rejection of 96.7% (the rejection of NF 270 was 97%). [ABSTRACT FROM AUTHOR]

The crystal structure of poly(4,4′-diphenylsulfonyl terephthalamide) ( pt-PSA) is studied by X-ray diffraction and molecular simulation. Although the number of observed reflections is limited to warrant a precise determination of the unit cell structure and symmetry, a reasonable monoclinic unit cell is suggested with dimensions of a = 0.645 nm, b = 0.488 nm, c = 3.010 nm, and γ = 122.5°. A twofold molecule with two monomeric units forming a large zigzag conformation satisfies the X-ray diffraction data. A layer structure is formed in the crystal phase, which is stabilized by the hydrogen bond between NH and CO and the parallel-displaced π-π stacking from the distortional coplanarity of the benzene rings and amide group. [ABSTRACT FROM AUTHOR]

Abstract: A new kind of high flux ultrafiltration (UF) membrane based on poly(vinyl alcohol) (PVA) electrospun nanofibrous scaffold support and PVA hydrogel coating has been demonstrated. The long-term performance of such membranes was optimized by a variation of degree of hydrolysis (i.e. 88–99%) and molecular weight (e.g. 13,000–124,000g/mol) in the electrospun PVA scaffold in conjunction with chemical crosslinking of PVA hydrogel coating. It was found that the electrospun scaffold fabricated by 96% hydrolyzed PVA with relatively high molecular weight (e.g. 85,000–124,000g/mol) exhibited very good overall mechanical performance before and after crosslinking. A PVA hydrogel coating, fabricated from the same material composition as the electrospun scaffold but different crosslinking conditions, was used as the anti-fouling layer for high-throughput water ultrafiltration. Results indicated that such unique hydrophilic nanofibrous composite membranes exhibited a flux rate (>130L/m2 h) significantly higher than commercial UF membranes but with similar filtration efficiency (rejection rate >99.5%). [Copyright &y& Elsevier]

Simultaneous measurements of Raman spectroscopy and synchrotron two-dimensional (2D) wide-angle x-ray diffraction (WAXD) have been successfully demonstrated for in situ study of an anisotropic system: isotactic polypropylene (iPP) fiber under tensile deformation. A fiber-optic probe was used to remotely deliver the incident laser beam on the sample as well as to collect the Raman signal based on the confocal arrangement, whereas high resolution 2D WAXD patterns were obtained simultaneously at the same position during deformation of polymers. The combined techniques yielded complementary information on the molecular structural evolution in both crystalline and amorphous phases. 2D WAXD results showed that the α-form iPP crystals were converted into the mesophase upon stretching at room temperature. Corresponding Raman spectra showed that characteristic bands from the crystal phase became weaker or disappeared during the transition from the crystal phase to the mesophase. However, the bands associated with the helical structure were still present, indicating the remainder of the helical conformation in the mesomorphic phase. The persistence of the Raman band at 812 cm[sup -1] in the mesophase implied that the structural difference between the crystal phase and the mesophase in iPP is due to the packing defects, rather than the conformational deviations from the (...TGTG...) sequence in chains. The variations in the Raman intensity ratio (I812/I843) indicated that the overall orientation of the fiber increased during stretching. The demonstrated techniques will be particularly useful for in situ studies of anisotropic polymers, where orientational dependent structural information from both crystalline and amorphous phases needs to be collected simultaneously. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Abstract: A novel class of high-flux thin film nanofibrous composite (TFNC) ultrafiltration membrane, consisting of UV-cured poly(vinyl alcohol) (PVA) hydro-gel barrier layer, electrospun nanofibrous PVA mid-layer scaffold and polyethylene terephthalate (PET) non-woven substrate, was investigated. The barrier layer was fabricated by photo-crosslinking of UV-reactive PVA (UV-PVA) on a chemically cross-linked nanofibrous PVA scaffold. The effects of concentration and viscosity of the UV-PVA solution on the flux and rejection rate of the TFNC membrane were studied. It was found that UV curing of a 5-wt% UV-PVA solution coating over 20-s time period yielded a high flux, high rejection UF membrane with good fouling resistance for separation of oil and water emulsion. [Copyright &y& Elsevier]

The design, construction and initial tests on a combined laser light scattering and synchrotron X-ray scattering instrument can cover studies of length scales from atomic sizes in Angstroms to microns and dynamics from microseconds to seconds are presented. In addition to static light scattering (SLS), dynamic light scattering (DLS), small angle X-ray scattering (SAXS) and wide angle X-ray diffraction (WAXD), the light scattering instrument is being developed to carry out studies in mildly turbid solutions, in the presence of multiple scattering. Three-dimensional photon cross correlation function (3D-PCCF) measurements have been introduced to couple with synchrotron X-ray scattering to study the structure, size and dynamics of macromolecules in solution.

A novel high flux filtration medium, consisting of a three-tier composite structure, i.e., a nonporous hydrophilic nanocomposite coating top layer, an electrospun nanofibrous substrate midlayer, and a conventional nonwoven microfibrous support, was demonstrated for oil/water emulsion separations for the first time. The nanofibrous substrate was prepared by electrospinning of poly(vinyl alcohol) (PVA) followed by chemical cross-linking with glutaraldehyde (GA) in acetone. The resulting cross-linked PVA substrates showed excellent water resistance and good mechanical properties. The top coating was based on a nanocomposite layer containing hydrophilic polyether-b-polyamide copolymer or a cross-linked PVA hydrogel incorporated with surface-oxidized multiwalled carbon nanotubes (MWNTs). Scanning electron microscopy (SEM) examinations indicated that the nanocomposite layer was nonporous within the instrumental resolution and MWNTs were well dispersed in the polymer matrix. Oil/ water emulsion tests showed that this unique type of filtration media exhibited a high flux rate (up to 330 L/m2-h at the feed pressure of 100 psi) and an excellent total organic solute rejection rate (99.8%) without appreciable fouling. The increase in the concentration of surface-oxidized MWNT in the coating layer generally improves the flux rate, which can be attributed to the generation of more effective hydrophilic nanochannels for water passage in the composite membranes.

Objectives: The objective of this study was to evaluate the efficacy of nonwoven bioabsorbable nanofibrous membranes of poly(lactideco-glycolide) for prevention of postsurgery-induced abdominal adhesions., Summary Background Data: Recent reports indicated that current materials used for adhesion prevention have only limited success. Studies on other bioabsorbable materials using a new fabrication technique demonstrated the promising potential of generating an improved and inexpensive product that is suitable for a variety of surgical applications., Methods: All rats underwent a midline celiotomy. The cecum was identified and scored using an abrasive pad until serosal bleeding was noted on the anterior surface. A 1 x 1 cm of abdominal wall muscle was excised directly over the cecal wound. The celiotomy was then closed in 2 layers immediately (control) after a barrier was laid in between the cecum and the abdominal wall. All rats underwent a second celiotomy after 28 days to evaluate the extent of abdominal adhesions qualitatively and quantitatively., Results: Cecal adhesions were reduced from 78% in the control group to 50% in the group using biodegradable poly(lactide-co-glycolide) (PLGA) nonwoven nanofibrous membranes (n = 10, P = 0.2) and to 22% in the group using membranes containing PLGA and poly(ethylene glycol)/poly(D,L-lactide) (PEG-PLA) blends (n = 9, P = 0.03). Electrospinning method also enabled us to load an antibiotic drug Cefoxitin sodium (Mefoxin; Merck Inc., West Point, PA) with high efficacy. The electrospun PLGA/PEG-PLA membranes impregnated with 5 wt% cefoxitin sodium, which amounts to approximately 10% of the systemic daily dose typically taken after surgery in humans, completely prevented cecal adhesions (0%) in rats., Conclusions: Electrospun nonwoven bioabsorbable nanofibrous membranes of poly(lactide-co-glycolide) were effective to reduce adhesions at the site of injury using an objective rat model. The membrane acted as a physical barrier but with drug-delivery capability. The combined advantages of composition adjustment, drug-loading capability, and easy placement handling (relatively hydrophobic) make these membranes potentially successful candidates for further clinical evaluations.

In this study, hyaluronic acid (HA) was electro-spun and electro-blown to prepare nonwoven nanofibrous membranes. Critical parameters for processing and corresponding effects on the membrane morphology were investigated using the methods of rheology and scanning electron microscopy (SEM). During electro-spinning, the optimal HA concentration window for nanofibrous formation was determined within a narrow range of 1.3-1.5 w/v %, corresponding to a solution viscosity range of 3-30 Pa s at a shear rate of 1 s(-1). SEM results indicated that, with increases in (1) the total concentration by blending of low molecular weight HA, (2) the evaporation rate by the addition of ethanol, and/or (3) the feeding rate of solution, the electro-spinning performance for creating nanofibers was improved. However, the improvement was not sufficient to achieve a consistent production of high quality nonwoven nanofiber membranes. This problem was overcome by a new electro-blowing process using the combination of air flow and electro-spinning. Although air blowing at room temperature around the spinneret orifice did not exhibit a remarkable enhancement of nanofiber formation of HA, the performance was significantly improved with an increase in the air blowing rate. SEM results showed that the temperature of air-blowing was the most effective parameter in ensuring HA nanofiber formation. As the temperature of the blown air increased from 25 to 57 degrees C, the nanofiber formation became consistent and uniform. A high quality HA nonwoven membrane of nanofibers was successfully produced by blowing air at 57 degrees C with a 70 ft(3)/hr flow rate.

Dextran is soluble in both water and organic solvents, so it could be a versatile biomacromolecule for preparing nanofibrous electrospun membranes by blending with either water-soluble bioactive agents or hydrophobic biodegradable polymers for biomedical applications. We have formulated electrospun dextran membranes, and the effects of various processing parameters on the membrane properties were investigated. It was found that uniform nanofibrous dextran membranes could be formed by using water, DMSO/water, and DMSO/DMF mixtures as solvents through adjusting the processing conditions (solution concentration, voltage, and the distance between the electrode and the collecting plate). When water was used as a solvent, up to 10% (w/w) of bovine serum albumin (BSA) or lysozyme could be directly incorporated into the dextran electrospun membrane without compromising its morphology. No significant effect of the electrospinning process on lysozyme activity was observed. The composite electrospun membranes consisting of poly(D,L-lactide-co-glycolide) (PLGA) and dextran were obtained using DMSO/DMF (50/50, volume ratio) mixture as solvents. For cross-linking the electrospun membrane, dextran was modified by substitution of methacrylate groups at the hydroxyl sites. It was found that the electrospun membranes prepared from methacrylated dextran can be cured by UV irradiation in the presence of 1% of 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator.

Ibuprofen-loaded composite membranes composed of poly(lactide-co-glycolide) (PLGA) and poly(ethylene glycol)-g-chitosan (PEG-g-CHN) were prepared by electrospinning. The electrospun membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), mechanical evaluation and contact angle measurements. Shrinkage behavior of the membrane in buffer at 37 degrees C was also evaluated. It was found that PLGA glass transition temperature (Tg) decreased with increasing PEG-g-CHN content in the composite membranes, which results in a decrease in tensile stress at break but an increase in tensile strain of the membranes. The degree of shrinkage of these composite membranes decreased from 76 to only 3% when the PEG-g-CHN content in the membranes increased from 10 to 30%. The presence of PEG-g-CHN significantly moderated the burst release rate of ibuprofen from the electrospun PLGA membranes. Moreover, ibuprofen could be conjugated to the side chains of PEG-g-CHN to prolong its release for more than two weeks. The sustained release capacity of the PLGA/PEG-g-CHN composite membranes, together with their compliant and stable mechanical properties, renders them ideal matrices for atrial fibrillation.

Electrospun poly(glycolide-co-lactide) (PLA10GA90, LA/GA ratio 10/90) biodegradable nanofiber membranes possessed very high surface area to volume ratios and were completely noncrystalline with a relatively lowered glass transition temperature. These characteristics led to very different structure, morphology, and property changes during in vitro degradation, which were examined systematically. A shrinkage study showed that the electrospun crystallizable but amorphous PLA10GA90 membranes exhibited a very small shrinkage percentage when compared with the electrospun membranes of noncrystallizable poly(lactide-co-glycolide) (PLA75GA25, LA/GA 75/25) and poly(d,l-lactide). Although the weight loss of electrospun PLA10GA90 membranes exhibited a similar degradation behavior as cast thin films, detailed studies showed that the structure and morphology changes in electrospun membranes followed different pathways during the hydrolytic degradation. After 1 day of degradation in buffer solution at 37 degrees C, electrospun PLA10GA90 membranes exhibited a sudden increase in crystallinity and glass transition temperature, due to the fast thermally induced crystallization process. The continuous increase in crystallinity and apparent crystal size, as well as the decrease in long period and lamellae thickness, indicated that the thermally induced crystallization was followed by a chain cleavage induced crystallization process. The mass loss rate was accelerated after 6 days of degradation. The increase in glass transition temperature during this period further confirmed that the degradation of PLA10GA90 nanofibers was initiated from the amorphous region within the lamellar superstructures. A mechanism of structure and morphology changes during in vitro degradation of electrospun PLA10GA90 nanofibers is proposed.

A noncross-linked interpenetrating polymer network (IPN), consisting of poly(N,N-dimethylacrylamide) (PDMA) and polyvinylpyrrolidone (PVP, weight-average molecular weight M(w) = 1 x 10(6) g/mol) was synthesized by polymerizing N,N-dimethylacrylamide (DMA) monomers directly in PVP buffer solution and tested as a separation medium for double-stranded (ds)DNA analysis without further purification. Due to the incompatibility of PVP and PDMA, a simple solution mixture could incur a microphase separation and showed poor performance on dsDNA separation. However, a dramatic improvement was achieved by the formation of an IPN. We attributed the high sieving ability of IPN as due to an increase in the number of entanglements by the more extended polymer chains. Apparent viscosity studies showed that the IPN had a much higher viscosity than the simple mixture containing the same amount of PDMA and PVP. In 1 x Tris-borate-EDTA (TBE) buffer, the concentration ratio of PDMA and PVP had a great effect on the DNA separation. At optimal conditions, the 22 fragments in pBR322/HaeIII DNA were successfully separated within 15 min, with a resolution of better than 1.0 for 123/124 bp.