Solvent Evaporation Time Research Articles

Study of the optimization factors for preparation of heterogeneous reverse osmosis membranes

The influence of the preparation factors such as casting solution composition, different methods of coal modification, evaporation time of solvent and their optimization on performance of cellulose acetate heterogeneous reverse osmosis membranes have been studied. Three types of membranes were made from a blend of cellulose acetate (CA) and coal by weight ratios 1:1.5, 1:1.75 and 1:2. The powdered coal was modified with nitric acid and aryl diazonium salts in acetonitrile medium at constant modification time. The membranes were prepared by phase inversion process from a casting solution of cellulose acetate-coal and magnesium perchlorate in acetone water mixture at varying evaporation time of solvent at constant temperature using the same gelation medium. The composition of raw and modified coals was examined by IR spectroscopy. Membranes obtained with a casting solution composition of cellulose acetate-coal in weight ratios of 1:1.5 and 1:1.75, modified coals and longer evaporation time of solvent showed the best performance.

The high flux poly (m-phenylene isophthalamide) nanofiltration membrane for dye purification and desalination

The aromatic poly (m-phenylene isophthalamide) (PMIA) nanofiltration (NF) membrane with polyvinyl pyrrolidone (PVP) and LiCl as additives was fabricated by phase inversion. The effects of additive content in the casting solution, solvent evaporation temperature and evaporation time during membrane fabrication on the performance of the PMIA NF membrane were investigated. The rejection of the PMIA NF membrane for dyes Eriochrome black T, Eriochrome blue black B and Alizarine red were all over 98%, with a flux about 80 L/m 2h , while the rejection for NaCl was only about 5.5% when tested at 0.4 MPa. The PMIA NF membrane was applied in the desalination and purification process of Eriochrome black T and NaCl mixed solution. The flux increased largely with the increase of the operation pressure and the temperature, while the rejection for dye remained over 99%. The flux decreased with the increase of the concentration of dye and salt in the feed solution while the rejection for dye and salt remained relative stable. The desalination and purification experiment exhibits that the rejection for the dye remained over 99% throughout the whole experiment which indicated that the PMIA-NF membranes could be successfully applied in the dye purification and desalination process.

Tailoring bi-soft segment poly (ester urethane urea) integral asymmetric membranes for CO 2 and O 2 permeation

Integral asymmetric bi-soft segment poly (ester urethane urea) membranes are casted through a novel procedure where a reaction is introduced in the casting solutions preparation step of the phase inversion technique. Two reactive pre-polymers, the polypropylene oxide-based with three terminal isocyanate groups and the polycaprolactone diol with two terminal hydroxyl groups, are dissolved in a single solvent, dimethyl formamide and in a solvent mixture of dimethyl formamide (DMF)/diethyl ether (DEE) and the polymerization reaction is carried out in a homogeneous phase. The weight ratio of DMF/DEE is varied over 11, 5 and 3. The membrane casting is carried out at solvent evaporation times of 30 s, 60 s and 90 s. For all the membranes prepared, the cross-sections of the scanning electron microscopy (SEM) images display asymmetric structures dependent on the casting solutions composition and on the casting evaporation times. The carbon dioxide and oxygen volumetric fluxes measured at pressures ranging from 76 cmHg to 380 cmHg were correlated to the active layer thickness of the asymmetric membranes. The achievement of increasing the O 2 and the CO 2 permeation rates is the result of the casting of poly (ester urethane urea) asymmetric membranes with the minimization of the thickness of the dense layers. This is coupled with the introduction of the reactive caprolactone pre-polymer that enhances hemocompatibility. These are two strong assets for membrane blood oxygenators.

Self-healing capability of porous polymer film with corrosion inhibitor inserted for corrosion protection

Porous polymer films with varying pore sizes were prepared by changing the evaporation time of an organic solvent. A specimen was prepared consisting of porous polymer film containing corrosion inhibitor coated onto carbon steel. The specimens were scratched with a knife-edge, and the polarization resistance was monitored in a sodium chloride solution. An increase in polarization resistance was confirmed, and the films with larger-sized pores demonstrated a higher self-healing capability.

Kinetic control of preparing honeycomb patterned porous film by the method of breath figure

In this article, linear and star-shaped poly(styrene- block-butadiene) copolymers have been used to study the kinetics of breath figure fabrication, which is a well known method to prepare honeycomb patterned porous film. The fabrication was carried out in an almost sealed chamber, in which a relatively stable water vapor was obtained by positioning some water in advance. The influences of the solvent evaporation speed and the water vapor pressure on the breath figure fabrication were studied. The effect of the starting polymer concentration on the formation of honeycomb porous pattern were investigated in detail. The results indicate that the polymer solution could reach a level of “solidification” to fix the condensed water droplets in a reasonable time of solvent evaporation, and to prevent the water droplets from coalescing. Therefore, a proper solvent vapor together with a fair fabrication temperature are required in order to obtain a honeycomb patterned porous film with good quality. The thus obtained honeycomb film was further UV irradiated for cross-linking to improve its properties such as solvent and thermal resistances, so that broadened applications of such films could be expected.

Experimental design and optimization of asymmetric flat-sheet membranes prepared for direct contact membrane distillation

Flat-sheet poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-HFP, membranes have been prepared using the phase inversion technique based on fractional factorial design. Combined effects of polymer and additive (polyethylene glycol, PEG) concentrations in the casting solutions, solvent evaporation time and coagulation bath temperature on the structural characteristics of the prepared membranes as well as on their direct contact membrane distillation (DCMD) performance have been investigated using statistical approach. The morphological properties of the membranes have been studied in terms of scanning electron microscopy, atomic force microscopy and void volume fraction. The factorial linear models have been developed to describe the main effects of factors on the DCMD responses namely, pure water permeation flux, permeate flux when using salt solution and salt rejection coefficient of the prepared membranes. Analysis of variance showed that all factors have significant effects on the responses. However, the coagulation bath temperature is the least influential factor, while the PVDF-HFP concentration has the greatest effects on both the permeate flux and the salt rejection coefficient. Optimization of membrane preparation conditions has been carried out using a minimum number of experiments and applying Lagrange multipliers optimization method. Under the obtained optimum conditions, 19.1 wt.% PVDF-HFP concentration, 4.99 wt.% PEG concentration, 35 °C coagulation bath temperature and 102 s solvent evaporation time, the prepared membrane exhibits the highest salt rejection coefficient, 99.95%, with a permeate flux of 4.41 L/h m 2.

Preparation, characterization and performance of Al 2O 3/PES membrane for wastewater filtration

Membrane bioreactors (MBRs) have been widely used as advanced wastewater treatment processes in recent years. However, membrane fouling and its consequences in terms of plant maintenance and operating costs limit the widespread application of MBRs. Thus great efforts have focused on fouling mitigation. In this study, Al 2O 3 entrapped polyethersulfone (PES) ultrafiltration membranes were prepared and applied to activated sludge filtration in order to evaluate their fouling characteristics. The impact of solvent evaporation time and polymer concentrations on ultrafiltration (UF) membrane characteristics and performance was studied. PES was employed as a base polymer, while N-methyl pyrrolidone (NMP) was used as a solvent. The flat sheet membranes, prepared via phase inversion, were characterized using scanning electron microscope (SEM). Membrane performance was changed by the addition of Al 2O 3 nanoparticles to the casting solution. Al 2O 3 entrapped membrane showed lower flux decline compared to that of neat polymeric membrane. Fouling mitigation effect increased with nanoparticle content. No significant effect of the nanoparticles distribution pattern inside the membrane matrix was found on the membrane performance. This study highlights the potential of Al 2O 3 immobilized membranes in MBR application.

Importance of the Spreading Solvent Evaporation Time in Langmuir Monolayers

Herein, it is shown that aromatic spreading solvents can be detected using in situ UV spectroscopy at the air−water interface beyond the common accepted time for evaporation of 10−20 min in the preparation of a Langmuir monolayer. Toluene and benzene, even though not significantly surface active, can be detected, and their behavior as a function of time and temperature is investigated. To our knowledge, this is the first time that the vibrational fine structure of the benzenoid bands are detected at the air−water interface.

Self‐Organization, Optical, and Electrical Properties of α‐Quinquethiophene–Dinucleotide Conjugates

The synthesis and properties of (5')TA(3')-t5 (8a) and (5')CG(3')-t5 (8b) conjugates, in which the self-complementary dinucleotides TA and CG are covalently bound to the central ring of alpha-quinquethiophene (t5), are described. According to molecular mechanics calculations, the preferred conformation of both 8a and 8b is that with the dinucleotide folded over the planar t5 backbone, with the nucleobases facing t5 at stacking distance. The calculations show that the aggregation process of 8a and 8b is driven by a mix of nucleobase-thiophene interactions, hydrogen bonding between nucleobases (non Watson-Crick (W&C) in TA, and W&C in CG), van der Waals, and electrostatic interactions. While 8b is scarcely soluble in any solvents, 8a is soluble in water, indicating that the aggregates of the former are more stable than those of the latter. Microfluidic-induced self-assembly studies of 8a showed the formation of lamellar, spherulitic, and dendritic supramolecular structures, depending on the concentration and solvent evaporation time. The self-assembled structures displayed micrometer dimensions in the xy plane of the substrate and nanometer dimensions in the z direction. Spatially resolved confocal microscopy and spectroscopy showed that the aggregates were characterized by intense fluorescence emission. Cast films of 8a from water solutions showed chirality transfer from the dinucleotide to t5. The hole mobility of the cast films of 8a was estimated using a two-electrode device under high vacuum and found to be up to two orders of magnitude greater than those previously measured for dinucleotide-quarterthiophene conjugates under the same experimental conditions.

Preparation and characterization of novel hydrophobic/hydrophilic polyetherimide composite membranes for desalination by direct contact membrane distillation

Two different types of hydrophobic surface modifying macromolecules (SMMs) were synthesized and characterized for fluorine content, average molecular weight and glass transition temperature. The synthesized SMMs were blended into polyetherimide (PEI) hydrophilic host polymer to form porous hydrophobic/hydrophilic composite membranes by the phase inversion method. The prepared membranes were characterized by the contact angle measurements, X-ray photoelectron spectroscopy test, gas permeation test, liquid entry pressure of water and scanning electron microscopy. Finally, these membranes were tested for desalination by direct contact membrane distillation (DCMD). Different parameters affecting the membrane preparation process were studied and their effects on the membrane morphology as well as on the membrane performance in desalination by DCMD were identified. These parameters include the SMMs type, SMMs concentration, solvent type and solvent evaporation time before gelation. An attempt to link the membrane morphology to its performance in DCMD is presented. This leads to better understanding of the effect of the membrane preparation on its performance. It was found that increasing the solvent evaporation time before gelation decreased the membrane flux since smaller pore sizes were observed. The membranes with higher contact angles and fluorine contents (more hydrophobic) exhibited smaller permeate fluxes. The membranes having sponge-like structures at the hydrophilic layer exhibited higher fluxes than those having finger-like structure at the hydrophilic layer. Moreover, the results were compared to a commercial polytetrafluoroethylene (PTFE) membrane. It was observed that most of the SMMs blended PEI membranes achieved better DCMD fluxes than those of the commercial membrane. A permeate flux 55% higher than that of PTFE was achieved. For both PTFE commercial membrane and all SMMs blended PEI membranes, the NaCl separation factor was found to be higher than 99% except for the PEI membrane prepared without SMMs.

Organic Solar Cells Using Nanoimprinted Transparent Metal Electrodes

Cost effective and highly efficient renewable energy is becoming ever more important in our age of rising energy prices and global climate change. Solar energy is a nonexhaustible and green energy. Organic solar cells (OSC) have the merits of low cost and simplistic fabrication in addition to compatibility with flexible plastic substrates over large areas. They have therefore been considered a promising energy conversion platform for clean and carbon-neutral energy production. In recent years, the power conversion efficiency of OSCs based on conjugated polymers has steadily increased through improved energy harvesting, enhanced exciton separation in improved device structures, and optimization of processing parameters, e.g., solvent evaporation time, and annealing conditions. Most OSCs are built on indium tin oxide (ITO) coated substrates because ITO offers transparency in the visible range of the electromagnetic spectrum as well as good electrical conductivity. However, ITO is not the optimum electrode for solar cell applications as it has been reported that the band structure of ITO hinders efficient photocurrent generation. Moreover, the poor mechanical stability of ITO can cause device failure when an ITO-coated flexible substrate is bent. In addition, the limited supply of indium and the increasing demand from the rapidly expanding display market have increased the cost of ITO drastically, which potentially prevents the realization of low cost and large scale OSC fabrication. Therefore, there is a strong need to find alternative materials that can replace ITO as high transparency electrode. Some examples that have been investigated recently are nanotube networks, and Ag wire grids. In this communication, we report on high transparency metal wire grid electrodes for organic solar cell applications. The high transparency metal electrodes are fabricated by nanoimprint lithography (NIL), and have several advan-

Processing of thin SU-8 films

This paper summarizes the results of the process optimization for SU-8 films with thicknesses ⩽5 µm. The influence of soft-bake conditions, exposure dose and post-exposure-bake parameters on residual film stress, structural stability and lithographic resolution was investigated. Conventionally, the SU-8 is soft-baked after spin coating to remove the solvent. After the exposure, a post-exposure bake at a high temperature TPEB ⩾ 90 °C is required to cross-link the resist. However, for thin SU-8 films this often results in cracking or delamination due to residual film stress. The approach of the process optimization is to keep a considerable amount of the solvent in the SU-8 before exposure to facilitate photo-acid diffusion and to increase the mobility of the monomers. The experiments demonstrate that a replacement of the soft-bake by a short solvent evaporation time at ambient temperature allows cross-linking of the thin SU-8 films even at a low TPEB = 50 °C. Fourier-transform infrared spectroscopy is used to confirm the increased cross-linking density. The low thermal stress due to the reduced TPEB and the improved structural stability result in crack-free structures and solve the issue of delamination. The knowledge of the influence of different processing parameters on the responses allows the design of optimized processes for thin SU-8 films depending on the specific application.

Optimization of formulation variables for the development of long acting microsphere based depot injection of olanzapine

This work was aimed to optimize the composition of microspheres of olanzapine to design long acting depot injection for the treatment of psychosis. Solvent evaporation method was used for the fabrication of microspheres. Different formulation variables for the solvent evaporation method, viz., effect of theoretical drug loading, type of surfactant and its concentration, temperature, volume of external phase and presence of salt in external aqueous phase, conditions and time of solvent evaporation and drying methodology were optimized. The microspheres were characterized for encapsulation efficiency, particle size, surface morphology, residual solvent content, drug release profile and drug release kinetics. The optimized formulation showed consistent drug release for upto 14 days time period.

Silica cages with controllable frameworks: synthesis, structure-tailoring, and formation mechanism

A simple method was developed for the synthesis of novel macroporous silica cages with tailored pore architecture and high thermal stability. The silica cages possess anamorphic spherical morphology and narrow particle size distribution (∼1.5 µm), consisting of numerous channels interconnected with one another to form a fully open three-dimensional network. The morphology and structure of macroporous silica cages are strongly affected by synthetic conditions, including the molar compositions of reactants, the evaporation time of solvent, and the aging conditions. The number of silica crystal nuclei in the synthesis system is the major factor that determines the formation of silica cages and the disorder-to-order transformation, which can be controlled by changing the reactant molar concentrations and the solvent evaporation time. Using the appropriate aging time in ethanol provides the possibility of effecting the transformation from disordered twisting silica nanofibers with random branches to silica cages. The transformation from the macroporous cages to the mesostructures and the formation mechanism of the cages are also discussed in detail.

Effects of preparation conditions on the surface modification and performance of polyethersulfone ultrafiltration membranes

AbstractThe impact that some membrane preparation steps had on ultrafiltration (UF) membrane characteristics and performance was studied. Polyethersulfone (PES) was employed as base polymer, while N‐methyl pyrrolidone (NMP) was used as a solvent, and polyvinylpyrrolidone (PVP) was used as a nonsolvent pore‐forming additive. The manufacturing variables studied were solvent evaporation time and membrane surface modification, using a fluorine‐based copolymer referred to as surface‐modifying macromolecule (SMM). The flat sheet membranes, prepared via phase inversion, were characterized using solute transport data, X‐ray photoelectron spectroscopy (XPS), and contact angle measurements. Membrane performance was evaluated via filtration test protocol that included a 6‐day filtration of concentrated river water. The flux reduction with time was modeled using single and dual mechanisms of fouling. The pore blockage/cake filtration model described better the behavior of the permeation rate along the experiments. Increasing the solvent evaporation time decreased the size of the pores and the permeation rate. However, it did not significantly affect the removal of the organic compounds naturally present in the river water used as feed. XPS and contact angle measurements proved that the short evaporation periods did not allow enough SMM migration to the surface to provoke a significant effect on the membrane performance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006

Analysis of Captan on Nitrile Glove Surfaces Using a Portable Attenuated Total Reflection Fourier Transform Infrared Spectrometer

This study developed a method to produce uniform captan surface films on a disposable nitrile glove for quantitation with a portable attenuated total reflection Fourier transform infrared (ATR-FTIR) spectrometer. A permeation test was performed using aqueous captan formulation. Uniform captan surface films were produced using solvent casting with 2-propanol and a 25 mm filter holder connected to a vacuum manifold to control solvent evaporation. The coefficient of variation of the reflectance at 1735 +/- 5 cm(-1) was minimized by selection of the optimum solvent volume, airflow rate, and evaporation time. At room temperature, the lower to upper quantifiable limits were 0.31-20.7 microg/cm2 (r = 0.9967; p < or = 0.05) for the outer glove surface and 0.55-17.5 microg/cm2 (r = 0.9409; p < or = 0.05) for the inner surface. Relative humidity and temperature did not affect the uncoated gloves at the wavelength of captan analysis. Glove screening using ATR-FTIR was necessary as a control for between-glove variation. Captan permeation, after 8 hours exposure to an aqueous concentration of 217 mg/mL of Captan 50-WP, was detected at 0.8 +/- 0.3 microg/cm2 on the inner glove surface. ATR-FTIR can detect captan permeation and can determine the protectiveness of this glove in the field.

Membrane surface modification and characterization by X-ray photoelectron spectroscopy, atomic force microscopy and contact angle measurements

Surface modifying macromolecules (SMMs) were used to modify the top surface of polymeric membranes. SMMs are oligomeric fluoropolymers synthesized by polyurethane chemistry and tailored with fluorinated end groups. In this study, the surface of polyetherimide (PEI) flat-sheet membranes prepared by the phase inversion method was modified using 2wt.% of SMM and 15wt.% PEI concentration in the polymer casting solution. The effect of solvent evaporation time on membrane surface modification was investigated. X-ray photoelectron spectroscopy analysis shows enrichment of fluorine on the modified PEI membrane surfaces and their contact angles were higher than those of the unmodified PEI membrane. Both the surface fluorine content and contact angles of the SMM/PEI blended membrane increased when the solvent evaporation time was increased up to 5min. The SMM modified and unmodified PEI membranes were characterized by means of tapping mode atomic force microscopy (TM-AFM). The mean pore size, nodule size, pore density, surface porosity and mean roughness of the modified membranes were determined and compared with those of the unmodified membrane.

Influence of processing conditions on the properties of ultrafiltration membranes

The effect of four processing variables on the final properties of ultrafiltration (UF) membranes was investigated. Flat-sheet polyethersulfone (PES) membranes were prepared by wet phase inversion. The variables of interest were: the concentration of base polymer in the casting solution (dope solution), the solvent evaporation time, the addition of surface modifying macromolecules (SMMs), and the use of the additive polyvinylpyrrolidone (PVP). The membranes were characterized by solute transport and scanning electron microscopy (SEM). No appreciable difference between the structures of surface–modified and unmodified membranes was observed by SEM. Membranes prepared with PVP had pure water permeation rates (PWP) significantly higher than membranes prepared without the PVP additive. However, the average polyethylene glycol (PEG 35 ku (35 kDa)) separation by membranes with PVP was approximately 15% lower than the tightest membranes prepared without PVP. The effect of surface modification with fluorinated additives and solvent evaporation time was observed only with high molecular weight cut-off (MWCO) membranes prepared with 12 wt.% PES casting solution.

Manufacturing conditions of surface-modified membranes: effects on ultrafiltration performance

The treatment of surface water was studied using different experimental ultrafiltration surface-modified polyethersulfone membranes. They were prepared adjusting three membrane-manufacturing variables: addition of three surface modifying macromolecules (SMMs), the solvent evaporation time and the polyethersulfone concentration in the casting solution. Membrane performance was evaluated in terms of total organic carbon removal, the amount of natural organic matter deposited on top of the membrane after filtration, the permeate flux and the flux reduction. In order to define the manufacturing conditions resulting in the “best membrane”, in addition to the performance results, other considerations such as membrane strength and SMM compatibility were necessary. Membranes prepared with a novel polypropylene diol-based additive proved to have a positive effect on the treatment of this particular surface water. A trade-off between total organic carbon removal and permeate flux, and a logical connection between membrane characteristics and performance were observed. Membranes with small molecular weight cut-off (and pore size) had high total organic carbon removals and low-permeate fluxes, consequently, fouling was small.

Full Finite Element Analyses for Leveling of a Polymer/Solvent Film Accompanying with Drying Shrinkage

A mathematical model for the leveling process of a polymer/solvent film coated on a flat substrate was constructed by employing a two-dimensional finite element analysis, in which the film thinning due to solvent evaporation was taken into account in addition to the spatial and temporal variations of the physical properties. Then, the effects of the solvent evaporation rate, the wavelength, and amplitude of disturbances on the leveling behavior were numerically investigated. As a result, the critical value of the Biot number, beyond which the coated film with irregular surface geometry is frozen due to the completion of solvent evaporation before the film surface becomes uniform by leveling, decreased with increasing wavelength of disturbances. Also, the leveling time at which the film becomes flat by leveling increases rapidly with the Biot number, and then the shortest drying time could be found as the time at which the leveling time coincides with the time of complete solvent evaporation.