Light Transmittance Experiments Research Articles

Effect of adding carbon quantum dots to a NMP solution of cellulose acetate on the formation mechanism of ensuing membrane

BackgroundCarbon quantum dots (CQDs) can improve membrane separation efficiency and significantly contribute to solving global problems. Investigating the influence of adding CQDs on phase separation of cellulose acetate (CA)/ N-methyl-2-pyrrolidone (NMP) solution would provide more understanding of membrane formation. MethodsCA+CQDs membrane was fabricated through non-solvent induced phase separation, using water as coagulant. Kinetic and thermodynamics behavior of polymer solution affected the phase separation mechanism. The thermodynamic behavior was observed in cloud-point curve from the ternary phase diagram of CA/NMP/water, whereas the kinetic was studied by correlating the viscosity of the dope with light transmittance experiment and optical microscope observation. Fourier transform infrared microscope measured the time of phase separation at different depths of the casting plate. Significant findingsAdding CQDs can affect both the kinetics and thermodynamic behavior CA/NMP solution. At the top of the casting plate, phase separation behavior was affected mainly by the formation of pseudo water layer, causing fast demixing rate with more porous structure. In the inner part, phase separation was facilitated by kinetic of the dope. The 1,000 ppm CQDs added CA membrane delivered the highest pure water flux of 731.90 ± 68.27 L·m−2·h−1 (1 bar).

Microprobe electrode array with individual interconnects through substrate using silicon through-glass via

This paper presents the fabrication and measurements of a vertical out-of-plane microprobe electrode array with individual interconnects through the substrate using a silicon through-glass via (TGV) with transparent properties. The TGV was fabricated using a low-resistance silicon (LRS) via and the glass reflow process. The microprobe structure was formed by multiple deep reactive ion etching and reactive ion etching processes using one-step photolithography and a single etch mask. The height and pitch of the microprobe are designed to be 90 μm and 210 μm, respectively. Cr and Au conductive layers were deposited and patterned on the silicon microprobe structure. A parylene-C thin film was used as an insulating layer and it was etched only at the tip-end through the self-alignment fabrication process using a thick photoresist to expose the conductive part. Each microprobe electrode was independently connected to the backside of the substrate through the silicon TGV. The single via resistance was measured to be 1.26 ± 0.041 Ω. To verify the electrochemical characteristics of the microprobe electrodes with individual interconnects, the steady-state limiting current through the redox reaction was measured by the cyclic voltammetry method for each electrode. The measured steady-state peak current of the microprobe electrode was compared with the theoretical calculation. Further, the electrode impedance was measured and the equivalent circuit analysis was constructed using the Zview impedance modeling software. Experiments were conducted to measure the impedance of 16 microprobe electrodes, and it was confirmed that the impedance did not exceed 1 MΩ at 1 kHz. Then, primary rat cortical neuron cells (DIV 7) were cultured on the fabricated microprobe electrodes and neural spike signals were successfully measured. Also, the light transmittance experiment was conducted to measure the transparency of the TGV structure fabricated through the glass reflow process.

Electro-optical, thermal and dielectric properties of ternary mixture of E7/6CB/6BA liquid crystal mixture complex

In this study, a novel liquid crystal mixture complex was designed and synthesized from the nematic liquid crystal mixture E7, hexylcyanobiphenyl (6CB) and hexylbenzoic acid (6BA). The thermal and morphological properties were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The DSC and POM results show that the liquid crystal complexes exhibit liquid crystalline properties with smectic and nematic phase. While the E7 ratio is 80%, the mixture complex has the widest nematic range and exhibits E7 properties. When the E7 weight ratio is less than 80%, with the formation of hydrogen bonds the number of mesogenic phases increases and the nematic range decreases. The electrical properties of obtained samples were measured by impedance spectroscopy technique. The birefringence and contrast ratio of samples also investigated by the help of light transmittance experiment.

Thermal and electro-optic properties of graphene oxide-doped hexylcyanobiphenyl liquid crystal

Hexylcyanobiphenyl liquid crystal was doped with graphene oxide at ratios %0.25GO, %0.5GO, %1GO and %2GO, and the change in physical properties of pristine and the doped liquid crystals has been investigated. The phase transitions of prepared samples were studied by differential scanning calorimeter and polarized optical microscopy. The differential scanning calorimeter and polarized optical microscopy results are in good agreement when examining the nematic–isotropic liquid phase transition temperatures of the hexylcyanobiphenyl. The liquid crystal texture images obtained with polarized optical microscopy reveals that thermal stability of sample changed with graphene oxide concentration, i.e., increased with graphene oxide concentration. Impedance, capacitance, conductivity and real and imaginary dielectric constants of the pure and doped liquid crystals were obtained depending on frequency and voltage at the room temperature by using impedance analyzer. These electrical properties of the pure and the graphene oxide-doped samples showed an increase with increasing the graphene oxide ratio. The voltage-dependent light transmittance experiment revealed that threshold voltage of LC cells decreased for %0.25GO- and % 1GO-dispersed samples, but it was increased at %0.5GO- and %2GO-dispersed samples.

Fouling behavior of urban sewage on binary blend PVDF UF membrane

Polyvinylidene fluoride (PVDF) ultrafiltration membranes with better performance were prepared by blending with PVA, polyvinylpyrrolidone, polyethylene glycol, and polymethylmethacrylate through phase inversion via immersion precipitation method. Phase inversion progress of membranes was investigated though light transmittance experiment. Membrane components and morphologies were analyzed by FTIR, scanning electron microscopy, and atomic force microscopy, respectively. Membrane performance was evaluated in terms of pure water permeation, BSA rejection, and water contact angle. Membranes fouling behavior was evaluated according to dynamic fouling resistance analysis, using secondary effluent of urban sewage as separation object. The results showed that PVDF UF membranes with high hydrophilicity, dense surface, and through macrovoids in cross-section had small sewage flux decline and low fouling during filtration, and the main fouling resistance was due to concentration polarization and cake layer resistance, and membrane fouling was reversible. While the UF membranes with porous surface, not through internal macrovoids, and loose sponge-like structure were trend to bring about pore plugging resistance, and membrane fouling was irreversible. The surface roughness had certain influence on the antifouling performance of PVDF UF membranes.

Effects of Sugars on the Light Transmittance of Tapioca Starch Pastes during Cold Storage

The aim of this study is to study the influence of sugars (glucose, sucrose and trehalose) on the light transmittance of Tapioca Starch (TS) gels during cold storage. The effects of sugars on the light transmittance of TS gels were investigated at the concentration of starch 2% (w:w) during cold storage. The results showed the light transmittance of TS gels could be improved by sugar addition, according to the sugar type and concentration. The light transmittance increased with the increase of the concentration of the same kind of sugar. And the improvement of light transmittance with the sugar type was according to the order: trehalose>sucrose>glucose. Whether addition of sugar or not, light transmittance decreased with the extension of storage days. Therefore, light transmittance experiment is a simple and inexpensive method to study the effects of sugars on the retrogradation of starch gels with low-concentration.

Study of polymer concentration and evaporation time as phase inversion parameters for polysulfone-based SRNF membranes

The preparation of polysulfone (PSf) solvent resistant nanofiltration (SRNF) flat sheet membranes was investigated. Membranes were prepared via the phase inversion process by means of immersion precipitation. The membrane formation process was studied at the level of the casting solution composition (polymer concentration) as well as on the level of post-casting (evaporation time). Membrane preparation and filtration were performed in a high-throughput fashion. The performance of the synthesized membranes was tested in SRNF by measuring iso-propanol permeances and rejections of Rose Bengal. Rejections varied from 37% to 92% when the polymer concentration in the casting solution was increased from 13 to 25wt% and permeance decreased from 9.7 to 0.07L/m2h bar. When evaporation time increased from 0 to 120s, rejections increased from 47% to 76% and permeance decreased from 2.37 to 0.08L/m2h bar. Scanning electron microscopy (SEM) was used to investigate the morphology of the membrane cross sections. Viscosity measurements and light transmittance experiments were conducted in order to describe precipitation kinetics of PSf solutions. Depending on the evaporation time, polymer precipitation took place after 4–10s. Viscosity changed from 0.14 to 15.4Pas when the polymer concentration varied from 13 to 29wt%. Cloudpoint measurements were performed to determine the precipitation curve on a quasi-ternary diagram. The measurements were used to try to better understand the thermodynamic and kinetic aspects of membrane formation.

Effects of nucleating agents on the morphologies and performances of poly(vinylidene fluoride) microporous membranes via thermally induced phase separation

AbstractThe effects of nucleating agents on the morphology and performance of poly(vinylidene fluoride) (PVDF) microporous membranes via thermally induced phase separation were investigated. The nucleating agents studied were dicyclohexyl benzene amide (TMB‐5), 2,2‐methylene bis(4,6‐tertiary butyl phenol) sodium phosphate (TMP‐1), and 1,3 : 2,4‐di‐p‐methylbenzylidene sorbitol (DM–LO). Light transmittance experiments and differential scanning calorimetry (DSC) were performed to obtain phase diagrams of PVDF/tributyl citrate/di(2‐ethylhexyl) phthalate/nucleating agent doped solutions. The morphology and performance of the prepared PVDF microporous membranes were characterized with scanning electron microscopy and microfiltration experiments. The results show that the thermodynamics of liquid–liquid phase separation were not affected by the addition of the nucleating agents, but solid–liquid phase separation was influenced. The system with 0.3 wt % TMB‐5 had the fastest crystallization rate and a better nucleation ability. The PVDF microporous membranes had a partly closed, lacy bicontinuous structure with TMP‐1 and DM–LO, whereas the membrane with 0.3 wt % TMB‐5 had an interconnected bicontinuous structure. The pore size distribution became narrower with the addition of nucleating agent. With 0.3 wt % TMB‐5, the membrane had the minimum mean pore size (0.095 μm), a porosity of 80.3%, and a pure water flux of 270 L·m−2·h−1; these values were higher than those of the pure PVDF membrane. The performances of the membranes decreased with additions of TMB‐5 of greater than 0.3 wt %. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Quantitative optical analysis of filler dispersion degree in MWCNT–epoxy nanocomposite

Recently developed methodology of quantitative analysis based on optical analysis of filler particles’ area distributions is applied now to estimate the dispersion efficiency of multiwall carbon nanotubes in nanocomposite prepared by solution intercalation method. Experimental parameters of dispersing (temperature, duration and power level of ultrasonication) were optimized and the most effective experimental procedure was determined. The methodology of determination of dispersion parameter is proved by indirect method of light transmittance experiments. The nanocomposite specimens having lower dispersion parameter represented the highest transmittance over the nanocomposite specimens.

Evolution of the precipitation kinetics, morphology, and permeation performance of phenolphthalein poly(ether sulfone) hollow‐fiber membranes with polyvinylpyrrolidones of different molecular weights as additives

AbstractPhenolphthalein poly(ether sulfone) (PES‐C) hollow‐fiber ultrafiltration (UF) membranes were fabricated by wet spinning and dry‐jet/wet spinning (10‐cm air gap) processes with polyvinylpyrrolidones (PVPs) of different molecular weights as additives. Light transmittance experiments were performed to obtain insight into the precipitation kinetics of PES‐C/PVP/N‐methyl‐2‐pyrrolidone (NMP) dope solutions. The morphology and permeation performance of the prepared PES‐C hollow‐fiber membranes were well characterized and elucidated with scanning electron microscopy and UF experiments in addition to the precipitation kinetics. The thermal and mechanical properties of the membranes were also studied. Experiments demonstrated that all PES‐C/PVP/NMP dope solutions experienced instantaneous demixing with pure water as the coagulant, and the precipitation rate decreased as the molecular weight of PVP increased. A double, fingerlike structure occurred in the PES‐C hollow‐fiber membranes spun with PVPs of low molecular weight (10,000, 24,000, or 58,000) as additives; however, a spongelike structure occurred in the PES‐C membranes with PVP with a molecular weight of 1,300,000 because of its very low precipitation rate. The pure water permeation (PWP) flux decreased and the rejection of lysozyme increased for the prepared PES‐C membranes as the molecular weight of PVP increased. The largest PWP flux of 149 L m−2 h−1 bar−1 was acquired for dry‐jet/wet‐spun PES‐C membranes with PVP with a molecular weight of 10,000 as an additive. The rejection of bovine serum albumin for the prepared PES‐C membranes was greater than 98%, and the rejection of lysozyme ranged from 47.1 to 89.4%; this indicated typical UF membranes. The decomposition temperature of the PES‐C membranes containing PVP was lower than that of the original polymer and decreased as the molecular weight of PVP increased. The break strain and the elongation at break were enhanced as the PVP molecular weight increased. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Characterization of PVDF–PFSA hollow fiber UF blend membrane with low-molecular weight cut-off

Polyvinylidene fluoride (PVDF)–perfluorosulfonic acid (PFSA) hollow fiber ultrafiltration blend membranes were prepared by wet-spinning method. The effects of PVDF–PFSA and ethanol concentrations on the structure morphology and performance of blend membranes were investigated. The coagulation kinetics was studied by light transmittance experiments. Blend membranes were characterized in terms of morphology, pore size distribution, molecular weight cut-off, water permeation flux and rejection. The wetting and fouling properties of blend membranes were also examined. Based on the experimental results, more sponge-like structures existed in the cross section of the blend membrane prepared from the dope solution with the increase in PVDF concentration, but the membrane showed a worse permeation performance. The increase of PFSA resulted in the formation and development of the finger-like voids. It was also found that the finger-like macrovoids began growing up inside the nascent membrane. Such changes were proved by scanning electron microscopy (SEM). By introducing different concentrations of ethanol from 1 to 5 wt.% in PVDF–PFSA dope solution, thinner and more uniform finger-like voids appeared through the cross section, the pure water permeation flux, the mean effective pore size, molecular weight cut-off were increased. PVDF–PFSA hollow fiber UF blend membranes with low-molecular weight cut-off around 10,000 Da were obtained and the morphology was elaborately controlled.

Preparation and characterization of PVDF–PFSA blend hollow fiber UF membrane

Polyvinylidene fluoride (PVDF)–perfluorosulfonic acid (PFSA) blend hollow fiber ultrafiltration (UF) membranes were prepared by wet-spinning method using pure water as an external coagulation solution. Coagulation kinetics of PVDF–PFSA–DMAc system was measured by light transmittance experiment. Using PEG10000 ( M w = 10,000), lysozyme ( M w = 14,400), PEG20000 ( M w = 20,000) and BSA ( M w = 67,000), the separation performances of PVDF–PFSA blend hollow fiber UF membranes were obtained. Based on the experimental results, the delayed demixing process was observed for the dope solution M-1 without PFSA-H while the instantaneous demixing process was observed for the others with PFSA-H in the dope solutions M-2 to M-6. The precipitation rate increased with the increment of the PFSA-H concentration in PVDF–PFSA dope solution. The bore fluid solution with 95:5 DMAc:H 2O resulted in single finger-like voids for PVDF–PFSA-H UF membrane. The pure water permeation flux of PVDF–PFSA-H UF membranes firstly increased from <0.1 × 10 −5 to 119.1 × 10 −5 L m −2 h −1 Pa −1 (<0.1 to 119.1 L m −2 h −1 bar −1) for M-1 to M-4(1) and 137 × 10 −5 L m −2 h −1 Pa −1 (137 L m −2 h −1 bar −1) for M-4(2), and decreased from 119.1 × 10 −5 to 79 × 10 −5 L m −2 h −1 Pa −1 (119.1 to 79 L m −2 h −1 bar −1) for M-4(1), M-5 and M-6 as the PFSA-H concentration changed from 0% to 5% and total PVDF–PFSA-H concentration was 20 wt.%. The molecular weight cut-off (MWCO) of PVDF–PFSA blend hollow fiber UF membranes spun from 20 wt.% PVDF–PFSA-H concentration with 3–5 wt.% PFSA-H was about 20,000 while that spun from 22 wt.% PVDF–PFSA-H or PVDF–PFSA-Na concentration with 5 wt.% PFSA-H or PFSA-Na was about 10,000. As the W PFSA-H/ W PVDF increases from 2/18 to 5/15 for M-3–M-6, J BSA/ J w increases from 0.53 to 0.79. The anti-fouling property of PVDF–PFSA-H blend UF membrane is superior to PVDF–PFSA-Na blend membrane. Based on FTIR spectra, PFSA-H existed in PVDF–PFSA blend hollow fiber UF membranes. There is no obvious variation of the intensity of the characteristic peak at 983 cm −1 assigned to C–O–C group of PFSA-H molecules. This also illustrated that PVDF–PFSA-H blend hollow fiber UF membranes were stable.

An Experimental Study at an Abu Dhabi Reservoir of Asphaltene Precipitation Caused By Gas Injection

Summary This paper discusses experimental work associated with the evaluation of asphaltene precipitation for a field in Abu Dhabi, UAE. This reservoir is in the early stages of development and will be put on production using a combination of gas-, water-, and water-alternating-gas- (WAG) injection schemes in early 2006. The field has not shown operational problems resulting from asphaltene precipitation during primary production. Laboratory experiments using the transmittance of an optimized laser light in the near-infrared (NIR) wavelength (≈1600 nm) were used to first confirm the stability of asphaltene in the reservoir fluid. Two cases covering the expected extremes in terms of the field gas/oil ratio (GOR) were evaluated. Isothermal depressurization tests were also conducted at reservoir, wellhead, and separator temperatures (250, 190, and 130°C, respectively). Several additional light-transmittance experiments were conducted to evaluate the asphaltene-instability regions resulting from reservoir-fluid contact with various concentrations of rich gas and carbon dioxide (CO2). Measurements using high-pressure filtration were also collected to quantify the bulk precipitation of asphaltene with various molar concentrations of gas. Finally, tests were conducted using state-of-the-art technologies to evaluate the consistency of the initial NIR runs. These technologies involved the use of a spectral-analysis system (SAS) to evaluate asphaltene-particle size and growth rate and high-pressure microscopy (HPM) images to visually confirm the measurements. Results indicated that rich hydrocarbon gas in contact with reservoir fluid destabilizes asphaltene. The amount of the bulk precipitation increased with higher concentrations of rich gas in the reservoir fluid. Particle sizes were estimated to be in the range of 0.5 to 1 µm. The effect of CO2 was found to be less severe with regard to asphaltene instability.