Device Performance of a Tubular Membrane Dialyzer Incorporating Ultrafiltration Effects on the Dialysis Efficiency.

Membrane dialysis is one of the membrane contactors applied to wastewater treatment. The dialysis rate of a traditional dialyzer module is restricted because the solutes transport through the membrane only by diffusion, in which the mass-transfer driving force across the membrane is the concentration gradient between the retentate and dialysate phases. A two-dimensional mathematical model of the concentric tubular dialysis-and-ultrafiltration module was developed theoretically in this study. The simulated results show that the dialysis rate improvement was significantly improved through implementing the ultrafiltration effect by introducing a trans-membrane pressure during the membrane dialysis process. The velocity profiles of the retentate and dialysate phases in the dialysis-and-ultrafiltration system were derived and expressed in terms of the stream function, which was solved numerically by the Crank-Nicolson method. A maximum dialysis rate improvement of up to twice that of the pure dialysis system (Vw=0) was obtained by employing a dialysis system with an ultrafiltration rate of Vw=2 mL/min and a constant membrane sieving coefficient of θ=1. The influences of the concentric tubular radius, ultrafiltration fluxes and membrane sieve factor on the outlet retentate concentration and mass transfer rate are also illustrated.

Nanostructured polymers with embedded self-assembled networks: reversibly tunable phase behaviors and physical properties.

1,3:2,4-Dibenzylidene sorbitol (DBS) can self-assemble into nanofibrillar networks to form organogels in a variety of organic solvents and liquid polymers. In this study, we induced the formation of organogels in solid poly(ethylene glycol) (PEG) polymers. The DBS gels appeared at temperatures above the melting point of PEG. When the DBS/PEG systems were heated at higher temperatures, they exhibited transparent, clear solution states due to the collapse of the DBS networks. Upon cooling to room temperature, the DBS self-assembled nanostructures appeared again, followed by the solidification (crystallization) of PEG. These DBS/PEG systems possess three different phases (solid, gel and liquid) and can be tuned by changes in the composition and temperature. Using polarized optical microscopy, all the gel systems were found to exhibit spherulite-like morphologies. Small-angle X-ray scattering results revealed lamellar packing in these spherulite-like morphologies. Transmission electron microscopy verified that these features were formed due to the presence of DBS nanofibrillar networks consisting of fibrils that were approximately 10-20 nm in diameter. In addition, the crystallization of PEG was strongly templated by the existing DBS nanofibrils. Moreover, there were no significant distortions in the PEG crystal structures due to the confinement of PEG between the DBS nanofibrils.

Novel Composite Gel Electrolytes with Enhanced Electrical Conductivity and Thermal Stability Prepared Using Self-Assembled Nanofibrillar Networks.

Novel composite gel electrolytes were prepared using self-assembled organogels as scaffolds. Mixing silica with the low-molecular-weight poly(ethylene glycol) (PEG)-based electrolytes resulted in precipitation due to significant aggregation of silica. However, clear and transparent PEG-silica composite gel electrolytes were obtained with 1,3:2,4-dibenzylidene-d-sorbitol (DBS) organogels. The organogels resulted from the formation of DBS nanofibrillar networks in which the diameter sizes of the nanofibrils ranged from 10 to 100 nm, as observed by transmission electron microscopy. These three-dimensional nanofibrillar networks entrapped the silica and prevented its aggregation. The thermal properties, such as gel dissolution and thermal degradation temperatures, of the composite gels significantly increased with increasing silica content, as determined by polarizing optical microscopy and thermogravimetric analysis. The conductivity of the prepared composite gel electrolytes was clearly enhanced by increasing the silica content. The silica was well dispersed along the DBS nanofibrillar networks, establishing homogeneous microstructures and effective contact with other components of the electrolytes, leading to an increase in the conductivity.

Self-assembly behaviors of dibenzylidene sorbitol hybrid organogels with inorganic silica.

Molecular interactions, rheological behaviors and microstructures of 1,3:2,4-dibenzylidene-d-sorbitol (DBS)/poly(ethylene glycol) (PEG) organogel-inorganic silica hybrid materials are discussed in this study. DBS can dissolve in low-molecular-weight PEG to form organogels. The self-assembly behavior of these organogels was significantly influenced by the addition of the inorganic silica. The π interactions between the phenyl rings of DBS were not influenced by silica addition; however, the addition of silica affected the intermolecular hydrogen bonding of DBS, which interacts with PEG. The silica more likely interacted with PEG and decreased the intermolecular interactions between DBS and PEG, which resulted in an increase in the self-assembly of DBS. Therefore, the gel formation time and gel dissolution temperature increased as the amount of silica increased, as determined by dynamic rheological instruments. In addition, these organogel systems were all found to exhibit spherulite-like textures under polarized optical microscopy. The addition of silica and the increased DBS self-assembly in PEG resulted in a higher self-assembly temperature of the organogels. The higher temperature resulted in the presence of fewer nucleation sites and larger spherulite sizes in these systems. Small-angle X-ray scattering results demonstrated lamellar packing in these spherulite-like morphologies. Furthermore, the organogels with silica affected the intermolecular hydrogen bonding between DBS and PEG to facilitate the self-assembly of DBS, which resulted in increased diameter sizes of the DBS nanofibrils, as observed using scanning electron microscopy. It was observed that the silica was entrapped within these nanofibrillar networks.

Preparation of Nanowire Silica Inside Self-Assembled Sodium Bis(2-ethylhexyl) Sulfosuccinate (AOT) Gels.

In conventional sol-gel methods, gel formation occurs due to aggregation of particles into irregular shapes of larger size. In this study, we conducted hydrolysis-condensation reactions of tetraethyl orthosilicate (TEOS) within water-laden channels inside the space created by self-assembled AOT molecules to prepare regular and nanosized silica in self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) gels. The AOT gels were obtained by adding small amounts of water to organic solvents containing high concentrations of AOT. Adding silica significantly influenced the rheological properties and microstructures of these AOT/silica gels. Rheological studies showed that the storage modulus G' and loss modulus G″ of the AOT gel systems became very close and even crossed, indicating that the gel is "weak"; however, for the AOT/silica gel systems, the rheological data demonstrated that G' is greater than G″ at all frequencies, indicative of a real gel with a G' of approximately 10(5) pa. Small-angle X-ray scattering (SAXS) results showed that the gels initially had a hexagonal close-packed cylindrical structure with long-range order and transitioned to nonclose-packed cylindrical structures without long-range order as the silica formed. The cylinder is expected to comprise stacks of silica molecules surrounded by AOT molecules, and the radius of the cylinder is close to the sum of the length of one AOT molecule and half the size of one silica molecule. The rheological and SAXS data show that silica in the AOT/silica systems grew in the axial direction due to the confinement of these cylindrical structures, leading to nanowire silica structures. After removal of the AOT components, the nanowire silica was approximately 5-10 nm in diameter, as observed using transmission electron microscopy (TEM).

NiOx Electrode Interlayer and CH3 NH2 /CH3 NH3 PbBr3 Interface Treatment to Markedly Advance Hybrid Perovskite-Based Light-Emitting Diodes.

The performance of hybrid perovskite-based light-emitting diodes (LEDs) is markedly enhanced by the application of a NiOx electrode interlayer and moderate methylamine treatment. A hybrid perovskite-based LED exhibits a peak luminous efficiency of 15.9 cd A-1 biased at 8.5 V, 407.65 mA cm-2 , and 65 300 cd m-2 , showing a distinctive impact for future applications.

Novel poly(ethylene glycol) gel electrolytes prepared using self-assembled 1,3:2,4-dibenzylidene-D-sorbitol.

Gel electrolytes have usually been prepared by adding gelators or polymers to the liquid organic solvent-based electrolytes. In this study, we proposed a method to prepare gel electrolytes using gelators in liquid (low molecular weight) polymer-based electrolytes. Inexpensive 1,3:2,4-dibenzylidene-D-sorbitol (DBS) was chosen as a gelator for poly(ethylene glycol) (PEG)-based electrolytes at relatively low DBS concentrations. A series of gel electrolytes was produced by varying the DBS amounts, PEG molecular weights and PEG end groups. First, we found that DBS molecules self-assembled into 3-D networks consisting of nanofibrils that were approximately 10 nm in diameter, as measured by transmission electron microscopy; they exhibited spherulite-like morphologies under polarizing optical microscopy. Second, the dynamic rheological measurements demonstrated that the elastic modulus and the dissolution temperature of DBS-PEG gels increased with the increasing DBS content. The thermal degradation temperature of these gels also increased when the DBS concentration increased, as determined by thermogravimetric analysis. In addition, adding DBS may help to facilitate the dissolution of iodide and iodine in PEG due to its ether groups. Furthermore, the conductivity of the prepared DBS-PEG gel electrolytes was similar to that of the liquid PEG electrolytes (without DBS). When used in dye-sensitized solar cells (DSSC), the PEG-based electrolytes having inactive methyl end groups achieved the highest energy conversion efficiency among the tested cells. The efficiency of DSSC filled with our gel electrolytes remained basically the same over a one-month period, implying that the materials were relatively stable.

New phases found in reverse micelle systems with high concentrations of AOT.

This paper discusses the phase behavior, rheology, and structure of self-assembled sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle systems at high AOT concentrations. When the amount of AOT and w(o) (the molar ratio of water to AOT) were changed, many different phases were found, a fact which is not discussed in the literature. Opaque gel-like phase (phase separation) occurred with high concentrations of AOT in organic solvents without water. When the AOT concentration and w(o) were increased to 18-72 m and 2, respectively, the samples were gel-like and translucent. Dynamic rheological results indicate that the viscoelastic transition agreed with a multirelaxation time model. Small-angle X-ray scattering (SAXS) results imply that these samples showed a hexagonally close-packed cylindrical structure in which the diameter of a cylinder was ~2.5-3.0 nm, depending on the water contents. Moreover, these AOT cylinders self-assembled into fiber bundles with a diameter of 1-10 µm, as determined using a polarized optical microscope. As w(o) was increased to 2-6 in 72 m AOT samples, similar rheological and SAXS results were obtained. However, a different type of viscoelastic transition occurred, from multirelaxation to single-relaxation, when w(o) was increased to 7-11. The samples were in the transparent gel-like phase, and the structures determined by SAXS were a combination of hexagonally packed cylindrical and lamellar structure. The close-packed cylindrical structures had larger radii and shorter lengths with increasing w(o). Furthermore, when w(o) was increased to 12, the gel-like phase disappeared and a highly viscous solution was observed. This is because all the cylindrical structures collapsed and transformed into lamellar structures when the amount of water was further increased.

Effect of hydrophobicity of monomers on the structures and properties of 1,3:2,4-dibenzylidene-D-sorbitol organogels and polymers prepared by templating the gels.

The effects of hydrophobicity of monomers on the structures and properties of 1,3:2,4-dibenzylidene-D-sorbitol (DBS) organogels and nanostructured polymers prepared by templating the self-assembled organogels were investigated in this study. Hydrophobic styrene (St), hydrophilic methyl (methacrylate) (MMA), and their mixtures were chosen as the monomers. Though the gelation time varied, the average diameters (around 10 nm) of DBS nanofibrils found in the resulting organogels did not change significantly, for monomers of different hydrophobicity, as observed by transmission electron microscopy (TEM). Nonetheless, new structures, DBS microaggregates, appeared when the MMA content in the monomers was high enough. These irregular, micrometer-sized DBS structures (microaggregates) may have formed because the aggregated DBS molecules were influenced by the MMA monomers, due to the hydrogen bonding between DBS and MMA. This was confirmed by Fourier transform infrared (FTIR) spectroscopy and could also explain the differences in the gelation time of the DBS organogels: gels form more slowly in MMA than in St because of the competing interaction, hydrogen bonding, between DBS and MMA. Subsequently, we thermally initiated the free-radical polymerization of these St/MMA co-monomers. PS/PMMA copolymers were obtained, and no macroscopic phase separation occurred after the polymerization. Finally, the porous structures of the polymers produced by the solvent extraction of the DBS templates were observed, using TEM.

Thermal behavior and crystal structure of poly(L-lactic acid) with 1,3:2,4-dibenzylidene-D-sorbitol.

This study investigated the effect of 1,3:2,4-dibenzylidene-D-sorbitol (DBS) on the thermal behavior and crystal structure of poly(L-lactic acid) (PLLA) by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). Different PLLA crystal structures (α- or α'-form crystal) were found by the change of the DBS amount and PLLA crystallization temperature. The order and regular α-form of PLLA was favored as the DBS component was added. The α-form crystal formed more at lower temperatures. Therefore, the disorder-to-order (α'-to-α) phase-transition temperature of PLLA was found to shift at lower temperatures as more DBS content was added. In the proposed structure of PLLA with DBS, the DBS molecules are stacked together through π-π interaction to form a strand with the PLLA molecules by hydrogen bonding. Because of these interactions, PLLA could have a more regular structure with the addition of DBS. In addition, the equilibrium melting point and glass-transition temperature of PLLA were not significantly changed with the addition of DBS. However, the addition of DBS changed the crystal structure of PLLA and thus affected the crystallization rate of PLLA.

Optical design of automotive headlight system incorporating digital micromirror device.

In recent years, the popular adaptive front-lighting automobile headlight system has become a main emphasis of research that manufacturers will continue to focus great efforts on in the future. In this research we propose a new integral optical design for an automotive headlight system with an advanced light-emitting diode and digital micromirror device (DMD). Traditionally, automobile headlights have all been designed as a low beam light module, whereas the high beam light module still requires using accessory lamps. In anticipation of this new concept of integral optical design, we have researched and designed a single optical system with high and low beam capabilities. To switch on and off the beams, a DMD is typically used. Because DMDs have the capability of redirecting incident light into a specific angle, they also determine the shape of the high or low light beam in order to match the standard of headlight illumination. With collocation of the multicurvature reflection lens design, a DMD can control the light energy distribution and thereby reinforce the resolution of the light beam.

Novel polymeric nanocomposites and porous materials prepared using organogels.

We propose a new method for preparing polymeric nanocomposites and porous materials using self-assembled templates formed by 1,3:2,4-dibenzylidene sorbitol (DBS) organogels. DBS is capable of self-assembling into a 3D nanofibrillar network at relatively low concentrations in some organic solvents to produce organogels. In this study, we induced the formation of such physical cross-linked networks in styrene. Subsequently, we polymerized the styrene in the presence of chemical cross-linkers, divinyl benzene (DVB), with different amounts of DBS using thermal-initiated polymerization. The resulting materials were transparent, homogeneous polystyrene (PS) nanocomposites with both physical and chemical cross-links. The porous polymeric materials were obtained by solvent extraction of the DBS nanofibrils from the PS. Brunauer-Emmett-Teller (BET) measurements show that the amounts of DBS and DVB influenced the specific surface area after the removal of the DBS fibrils.

Nanostructured polymers prepared using a self-assembled nanofibrillar scaffold as a reverse template.

We describe the preparation of nanostructured polymeric materials by polymerizing a monomer within a scaffold composed of self-assembled nanofibrils. 1,3:2,4-Dibenzylidene sorbitol (DBS) is an inexpensive sugar derivative that can form nanofibrillar networks in a variety of organic solvents at relatively low concentrations. Here, we induce DBS nanofibrils in styrene and then thermally initiate the free-radical polymerization of the monomer. The polymerization proceeds without any evidence of macroscopic phase separation, ultimately yielding a transparent solid of polystyrene. Within this material, intact DBS nanofibrils (diameter 10-100 nm) are preserved, as shown by atomic force microscopy (AFM). The DBS fibrils can also be subsequently extracted from the polymer, leaving behind a network of nanoscale pores. The porosity of the resulting polymer has been characterized by the BET technique.

Condensed multilamellar structure of a complex of DNA with an amphiphilic block copolymer.

Deoxyribonucleic acid (DNA) is an attractive building block for self-assembled nanostructures, because the anionic phosphate group and the base moiety allow it to bind with a broad spectrum of organic and inorganic species through ionic and hydrogen bonding. Here we present a hierarchical structure formed by the ionic complex of DNA with an amphiphilic block copolymer comprising a cationic block. Upon the complexation the cationic block chains wrap around DNA for charge matching and the microphase separation between the hydrophobic block and the hydrophilic component yields a multilamellar structure with liquid crystalline ordering of the DNA chains condensed in the hydrophilic microdomains. Each hydrophilic lamellar domain is found to contain two DNA sublayers separated by a thin water gap, with each sublayer comprising two rows of densely packed DNA chains to lower the interfacial free energy for the present system with strong polar-nonpolar repulsion.

Analysis of rapid chain dynamics in isochronal dielectric measurements of polymers.

Fast dynamics within the microwave frequency range (approximately gigahertz) in polymer systems as a function of temperature (in the range from 20 to 190 degrees C) were studied using high frequency dielectric spectroscopy. The frequency of radiation was varied from 0.5 to 18 GHz. The isochronal dielectric loss data were taken to eliminate the complexity arising from the frequency-independent, temperature-dependent background loss in the condensed phase. These studies were conducted for poly(caprolactone) (PCL), poly(ethylene oxide) (PEO), poly(ethylene oxide) with methoxy end group (PEO-CH3), PLA-b-PEO-b-PLA triblock copolymers, and several polymers with high glass transition temperatures. These polymers possess glass temperatures ranging from -62 degrees C (PCL) to 110 degrees C (PMMA). One broad relaxation process was found only for polymers (PCL, PEO, and PLA-b-PEO-b-PLA) with low glass transition temperatures. The effect due to end groups was investigated by comparing the results of PEO with hydroxy versus methoxy end groups. The measured relaxation process was determined not to be associated with end groups. The results from temperature-dependent dielectric spectroscopy indicate that the relaxation process follows an Arrhenius T dependence suggesting that it is due to local motions. The activation energy of the relaxation process was measured and investigated based on the coupling model. The results suggest that the observed relaxation process behaves as a Johari-Goldstein beta relaxation.