Increasing Solution Conductivity Research Articles

Encapsulation of tannic acid in polyvinylidene fluoride mediated electrospun nanofibers and its antibiofilm and antibacterial activities

In the past 15 years or more, interest in polymer-mediated nanofibers (NFs), a significant class of nanomaterials, has grown. Although fibers with a diameter of less than 1 mm are frequently commonly referred to as NFs, and are typically defined as having a diameter of less than several hundreds of nanometers. Due to the increased antibiotic resistance of many diseases nowadays, NFs with antibacterial activity are quite important. A flexible technique for creating NFs with the desired characteristics is called electrospinning. This research article describes how to make electrospun NFs of tannic acid (TA) with polyvinylidene fluoride (PVDF) as the template. As a result, the absorbance of the obtained NFs has been raised without forming any additional peaks in the spectral ranges. The obtained NF has a gradual increase in intensity, and the FT-IR data show that the TA is present in the NFs. FE-SEM images show that the NFs are discovered to be completely bead-free. Since TA reduced the viscosity of the spinning solution while marginally increasing solution conductivity, PVDF NFs have a greater average fiber diameter (AFD) than NFs of TA with PVDF, which is likely a result of the TA solutions in it. The findings showed that TA greatly decreased S. aureus and E. coli’s ability to attach. The acquired NFs created in this work may have significant potential for reducing the pathogenicity of S. aureus and E. coli as well as their ability to build biofilms.

Unveiling the Mechanism of the in Situ Formation of 3D Fiber Macroassemblies with Controlled Properties.

Electrospinning technique is well-known for the generation of different fibers. While it is a "simple" technique, it lies in the fact that the fibers are typically produced in the form of densely packed two-dimensional (2D) mats with limited thickness, shape, and porosity. The highly demanded three-dimensional (3D) fiber assemblies have been explored by time-consuming postprocessing and/or complex setup modifications. Here, we use a classic electrospinning setup to directly produce 3D fiber macrostructures only by modulating the spinning solution. Increasing solution conductivity modifies electrodynamic jet behavior and fiber assembling process; both are observed in situ using a high-speed camera. More viscous solutions render thicker fibers that own enhanced mechanical stiffness as examined by finite element analysis. We reveal the correlation between the universal solution parameters and the dimensionality of fiber assemblies, thereof, enlightening the design of more "3D spinnable" solutions that are compatible with any commercial electrospinning equipment. After a calcination step, ultralightweight ceramic fiber assemblies are generated. These inexpensive materials can clean up exceptionally large fractions of oil spillages and provide high-performance thermal insulation. This work would drive the development and scale-up production of next-generation 3D fiber materials for engineering, biomedical, and environmental applications.

Role of sodium hexametaphosphate in ultra-fine grinding of alumina-doped titanium dioxide

In wet stirred milling of Al-doped TiO2, sodium hexametaphosphate (SHMP) is used as a small molecule dispersant to improve milling performance. In both acidic and basic conditions, SHMP interacts strongly with Al-doped TiO2 and remains stable during milling. Considering the apparent and true particle breakage performance, at pH 10.3, the optimal dosing concentration was 0.16 wt% (0.33θ, sub-monolayer coverage), which is consistent for both dilute (5 vol%) and concentrated (≥ 19.1 vol%) suspensions. At higher SHMP concentration (0.77θ), the increased solution conductivity compromised milling performance by weakly destabilizing the Al-doped TiO2 particles. At the optimal dose concentration of 0.33θ SHMP, particle dispersion is maintained through electrostatic and steric forces which contribute to moderating changes in suspension viscosity (~10% increase) as the particle size is reduced.

Influence of solution electrical conductivity and ionic composition on the performance of a gas–liquid pulsed spark discharge reactor for water treatment

The influence of solution electrical conductivity and ion composition on the performance of plasma reactors for water treatment applications is only partially understood. This study uses a point–point discharge over the surface of water in argon gas to determine the influence of solution conductivity, in the range of 0.3–45 mS/cm, on the physiochemical properties of spark discharges and the removal of two organic contaminants: perfluorooctanoic acid (PFOA) and Rhodamine B dye. The influence of various ions was also explored using chlorine and non-chlorine salts to adjust solution conductivity. The removal of PFOA increased with conductivity regardless of the salt type due to the salting out effect which increased PFOA's interfacial concentration. The removal of Rhodamine B dye depended on both salt type and solution electrical conductivity. In the presence of non-chorine salts, UV photolysis was the main mechanism for the dye degradation and its removal rate did not change with conductivity. The dye removal rate was the highest in the presence of chloride-based salts at the highest values of solution conductivities. In the presence of chorine salts, OH radicals are produced by the discharge generated hypochlorous acid, which is mixed into the bulk solution to react with the Rhodamine B dye. The generation rate of hydroxyl radicals appears to decrease with increasing solution conductivity, and these species are not directly involved in the degradation of the two compounds investigated in this study.

Step-by-step improvement of mixed-matrix nanofiber membrane with functionalized graphene oxide for desalination via air-gap membrane distillation

A straightforward three-stage method was applied to fabricate a super-hydrophobic mixed-matrix nanofiber membrane using the electrospinning method for desalination purpose. First, a hydrothermal technique was applied to synthesize a super-hydrophobic nano-sheet, called octadecylamine-reduced graphene oxide (ODA-rGO) with a water contact angle of 162°, which was then added to PVDF-HFP dope solution. After, 0.005 wt% LiCl was added to the dope solution to decrease the mean pore size by increasing solution conductivity. Moreover, some membranes were hot-pressed to improve liquid entry pressure (LEP). Eventually, a top-quality nanofiber membrane was synthesized using 0.1 wt% ODA-rGO and 0.005 wt% LiCl, and hot-pressed, named by MLH-0.1. By applying these stepwise improvements, the mean pore size reduced from 1.30 to 0.24 µm and LEP significantly increased from 30.4 to 127.6 kPa, compared to a neat electrospun nanofiber membrane. Finally, MLH-0.1 was tested in the air gap membrane distillation process for desalination of an aqueous solution containing 3.5 wt% NaCl. MLH-0.1 demonstrated the maximum flux of 21.1 kg/m2.h at temperatures of 70℃ and 20℃ for the feed and the permeation sides, respectively, as well as a remarkable and stable salt rejection of 99.99% for 4 days.

Quantifying the factors limiting performance and rates in microbial fuel cells using the electrode potential slope analysis combined with electrical impedance spectroscopy

Improving power generation of microbial fuel cells (MFCs) requires better methods to quantify the impact of the solution chemistry on performance. While buffer concentration and conductivity have been indicated to impact performance of flat (carbon cloth) anodes, we were able for the first to time to quantitatively determine the impact of the phosphate buffer solution (PBS) concentration separate from conductivity on electrode resistances of commonly used brush anodes and activated carbon cathodes. Using the electrode potential slope (EPS) method, we showed that the anode resistance decreased by 64% (from 14.6 ± 0.1 mΩ m2 to 5.3 ± 0.1 mΩ m2) by increasing the PBS concentration from 50 to 200 mM. There was no appreciable change in the cathode resistance (17.0 ± 0.1 mΩ m2, 50 mM; 18.9 ± 0.2 mΩ m2, 200 mM) although overall performance increased due to a larger cathode experimental working potential (ECat,e0-50= 268.9 ± 0.9 mV, ECat,e0-200= 370 ± 1 mV). Adding phosphate buffer to low conductivity synthetic wastewater containing 0.25 g L−1 sodium acetate decreased the anode resistance by 52% (from 59.1 ± 0.2 mΩ m2 to 28.1 ± 0.1 mΩ m2), but increasing only conductivity by adding NaCl or acetate had little impact on electrode resistances. Using electrochemical impedance spectroscopy (EIS), we determined the reasons for these responses. The cathode was limited by oxygen reduction reaction (ORR) kinetics, while the brush anode was limited by mass transfer (proton diffusion), consistent with the impact of buffer concentration on performance. These results have important implications for operation of MFCs as increasing solution conductivity alone, for example, by adding seawater, will not be sufficient to improve anode performance.

A comparative study on pre- and post-production plasma treatments of PCL films and nanofibers for improved cell-material interactions

In this work, an atmospheric pressure plasma jet (APPJ) has been used to modify a 5% polycaprolactone (PCL) solution, after which the PCL solution was spin coated or electrospun to generate PCL films and nanofibers respectively. The APPJ treatment was found to have no effects on the chemical and physical properties of the PCL films, however, a strong influence on the morphology of electrospun PCL nanofibers could be observed. PCL nanofibers generated from the pristine PCL solutions contained multiple beads, while the PCL nanofibrous material generated from the APPJ-treated solutions consisted of nicely elongated, beadless PCL nanofibers. This enhanced electrospinnability was attributed to the strongly increased solution conductivity induced by the APPJ exposure. The APPJ treatment was also found to have minor effects on the chemical composition and the wettability of the nanofibers, which could be linked to the different surface morphology. All investigated pristine and APPJ-treated films and nanofibers unfortunately possessed poor cell-material interactions as a result of their high hydrophobicity. To cope with this issue, after spin coating and electrospinning, a second surface modification treatment making use of a dielectric barrier discharge (DBD) sustained in argon was also conducted. These treatments were found to considerably increase the wettability of PCL films and nanofibers without affecting their surface morphology. The enhanced wettability was caused by the incorporation of CO functional surface groups by the performed DBD treatments. The treatments were also found to positively affect cell growth on PCL films and nanofibers, with the best cellular performance obtained for the APPJ/DBD-treated PCL nanofibers. A combination of plasma treatments can thus play a significant role in the preparation of ideal electrospun PCL scaffolds for tissue engineering applications.

Pitting Susceptibility of Concrete Reinforcing Steel Bars Having Manganese Sulfide Inclusions

Long-term wetting-drying treatment of specimens with reinforcing bars having manganese sulfide (MnS) inclusions in their microstructure showed a strong pitting tendency under sufficient chloride concentration. On the other hand, reinforcing bars free from MnS inclusions tested under identical conditions did not exhibit such pitting. The mass loss for both types of reinforcing bars computed after 3 years of exposure were comparable. However, the mortars embedded with manganese sulfide inclusion (MSI) reinforcing bars exhibited cracking after 3 years of wet/dry treatments. No such cracks were found for inclusion-free (IF) reinforcing bars. Scanning electron microscopy, space and time-dependent electro-chemical alternate current (AC) impedance, and potential studies were performed to examine the kinetics and mechanism of these reinforcing bars. The accelerating effect of chloride on pitting of metals and alloys with MnS inclusions has been explained in this paper considering the theory of acid regeneration cycle, increased solution conductivity, and the availability of high charge density on these ion forming compounds, which destabilized the passive layer. Raman spectroscopy and X-ray diffraction studies indicated the formation of ferric chloride in the rust layers of severely pitted MSI reinforcing bars. It is suggested that this ferric chloride, in the presence of oxygen and moisture, regenerated hydrochloric acid and lepidocrocite, resulting in autocatalytic chain reactions on the surface of MSI reinforcing bars.

Air Breathing Cathodes for Microbial Fuel Cell using Mn-, Fe-, Co- and Ni-containing Platinum Group Metal-free Catalysts

The oxygen reduction reaction (ORR) is one of the major factors that is limiting the overall performance output of microbial fuel cells (MFC). In this study, Platinum Group Metal-free (PGM-free) ORR catalysts based on Fe, Co, Ni, Mn and the same precursor (Aminoantipyrine, AAPyr) were synthesized using identical sacrificial support method (SSM). The catalysts were investigated for their electrochemical performance, and then integrated into an air-breathing cathode to be tested in “clean” environment and in a working microbial fuel cell (MFC). Their performances were also compared to activated carbon (AC) based cathode under similar conditions. Results showed that the addition of Mn, Fe, Co and Ni to AAPyr increased the performances compared to AC. Fe-AAPyr showed the highest open circuit potential (OCP) that was 0.307±0.001V (vs. Ag/AgCl) and the highest electrocatalytic activity at pH 7.5. On the contrary, AC had an OCP of 0.203±0.002V (vs. Ag/AgCl) and had the lowest electrochemical activity. In MFC, Fe-AAPyr also had the highest output of 251±2.3μWcm−2, followed by Co-AAPyr with 196±1.5μWcm−2, Ni-AAPyr with 171±3.6μWcm−2, Mn-AAPyr with 160±2.8μWcm−2 and AC 129±4.2μWcm−2. The best performing catalyst (Fe-AAPyr) was then tested in MFC with increasing solution conductivity from 12.4 mScm−1 to 63.1 mScm−1. A maximum power density of 482±5μWcm−2 was obtained with increasing solution conductivity, which is one of the highest values reported in the field.

Effect of electrical discharge in water on concentration of nitrate solution

In this work, the effect of electrical discharge on nitrate concentration is considered in aqueous solution. The atmospheric pressure plasma was produced by a high-voltage power supply at 27 kHz using pin-to-pin configuration. Air, argon, and argon/methane mixture were used to study the working gas effect. UV-VIS spectroscopy and ion chromatography were used to analyze the effect of the electrical discharge on nitrate concentration in deionized water. Optical emission spectroscopy (OES) was applied to diagnose active species inside and on the surface of the deionized water solution. The results of the present work showed that the atmospheric pressure electric discharge with air increases nitrate concentration while it remains constant using argon and argon/methane electrical discharges. It was also revealed that in the presence of air, the electrical discharge reduces pH, acidifying the solution and increasing solution conductivity due to production of extra nitrate ions. On the other hand, argon electrical discharge increases pH and conductivity due to production of OH- ion in water.

Fabrication of micro-patterns via near-field electrospray

A near-field electrospray process is developed to deposited micro-patterns. Compared with conventional electrospray, near field electrospray uses a steel probe instead of capillary nozzle, and its nozzle-to-substrate distance is shortened to several millimeters to realize micro-scale deposition area. The liquid is supplied by discretely dipping the probe into solution in advance so that electrospray process maintains until the consumption of liquid adhered at the probe tip. The influence of solution conductivity and applied voltage on deposition are investigated, as increasing solution conductivity and high applied voltage may promote the electrospray process and enlarge the line width. In addition, micro-patterns with various materials are directly electrosprayed.

Analysis of Electrical Discharge Plasma in a Gas‐Liquid Flow Reactor Using Optical Emission Spectroscopy and the Formation of Hydrogen Peroxide

Optical emission spectroscopy was used to characterize an electrical discharge plasma reactor with a liquid H2O film contacting different carrier gases. The plasma gas temperatures for Ar, He, and 1% N2 in Ar were 1000–1200 K and did not vary significantly with liquid flow rate. Increasing solution conductivity by adding KCl to deionized water in the Ar case lowered the temperature by 13%, increased the discharge power and lowered the H2O2 formation rates. The temperature was highest in the case of air (2400 K), and in the case of Ar the temperature increased with the addition of O2. The temperatures for this reactor are comparable to previous studies with discharges in humid gases, while the effects of liquid conductivity were similar to those reported with direct discharge in the liquid phase.

Electrospinning of unidirectionally and orthogonally aligned thermoplastic polyurethane nanofibers: fiber orientation and cell migration.

Unidirectionally and orthogonally aligned thermoplastic polyurethane (TPU) nanofibers were electrospun using a custom-built electrospinning device. The unidirectionally aligned fibers were collected using two parallel copper plates, and the orthogonally aligned fibers were collected using two orthogonal sets of parallel copper plates with alternate negative connections. Carbon nanotubes (CNT) and polyacrylic acid (PAA) were added to modify the polymer solution. It was found that both CNT and PAA were capable of increasing solution conductivity. The TPU/PAA fiber showed the highest degree of fiber orientation with more than 90% of the fibers having an orientation angle between -10° and 10° for unidirectionally aligned fibers, and for orthogonally aligned fibers, the orientation angle of 50% fibers located between -10° and 10° and 48% fibers located between 80° and 100°. Viability assessment of 3T3 fibroblasts cultured on TPU/PAA fibers suggested that the material was cytocompatible. The cells' orientation and migration direction closely matched the fibers' orientation. The cell migration velocity and distance were both enhanced with the guidance of fibers compared with cells cultured on random fibers and common tissue culture plastic. Controlling cell migration velocity and directionality may provide ways to influence differentiation and gene expression and systems that would allow further exploration of wound repair and metastatic cell behavior.

Role of solution conductivity in reaction induced charge auto-electrophoresis

Catalytic bimetallic Janus particles swim by a bipolar electrochemical propulsion mechanism that results from electroosmotic fluid slip around the particle surface. The flow is driven by electrical body forces which are generated from a coupling of a reaction-induced electric field and net charge in the diffuse layer surrounding the particle. This paper presents simulations, scaling, and physical descriptions of the experimentally observed trend that the swimming speed decays rapidly with increasing solution conductivity. The simulations solve the full Poisson-Nernst-Planck-Stokes equations with multiple ionic species, a cylindrical particle in an infinite fluid, and nonlinear Butler-Volmer boundary conditions to represent the electrochemical surface reactions. The speed of bimetallic particles is reduced in high-conductivity solutions because of reductions in the induced electric field in the diffuse layer near the rod, the total reaction rate, and the magnitude of the rod zeta potential. This work suggests that the auto-electrophoretic mechanism is inherently susceptible to speed reductions in higher ionic strength solutions.

Amine-functionalized thermoplastic polyurethane electrospun fibers prepared by co-electrospinning with 3-aminopropyltriethoxysilane and preparation of conductive fiber mats

Amine-functionalized thermoplastic polyurethane (TPU) electrospun fibers with controllable number of amine groups on fiber surfaces are prepared by co-electrospinning of TPU and 3-aminopropyltriethoxysilane (APS) in DMF/THF 4:6, followed by thermal treatment at 60 °C in a ventilated oven for 24 h. The morphology of the fibers was observed by Field Emission Scanning Electron Microscopy (FESEM), showing a decrease in average fiber diameter with increasing APS content, resulted from significantly increased solution conductivity. The amine groups are homogeneously distributed on the fiber surfaces, as revealed by energy dispersive X-ray spectroscopy (EDX) Si-mapping. Both the Si content measured by X-ray photoelectron spectroscopy (XPS) and NH2 content obtained by chemical titration show an enrichment of APS condensate on the fiber surfaces, which is explained by the higher mobility of APS to TPU during electrospinning. Gold nanoparticles of 16 nm are homogeneously adsorbed on the amine-functionalized TPU fibers. A conductive gold layer with a surface resistivity of 0.3 Ω/sq is formed after electroless plating using the adsorbed gold nanoparticles as the seeds, demonstrating the usefulness of the amine groups in the preparation of TPU fibers with added functionalities.

Electrospun PLA/PCL fibers with tubular nanoclay: Morphological and structural analysis

AbstractBiodegradable polymers are good candidates for a wide range of applications in tissue engineering and drug delivery because of their biocompatibility, their degradation, mechanical properties, and offer a sustained release of encapsulated drugs. The electrospun polymer nanofibrous materials can be used as carriers for hydrophobic and hydrophilic drugs. This research work focused on poly(lactic acid) (PLA) and blends of PLA with poly (ε‐caprolactone) (PCL) that are reinforced with different concentrations of halloysite nanotubes (HNTs) and various cosolvents for electrospinning including chloroform : acetone, chloroform : methanol, and dichloromethane (DCM) : N,N, dimethylformamide (DFM). The fibers produced from the DCM : DMF system without HNTs were more uniform resulting in smaller fiber diameters as compared to the chloroform: methanol system due to the increased solution conductivity. The addition of HNT nanoparticles produced electrospun fibers with large diameters because the viscosity of the solution increased. Cosolvent was important in determining fiber diameters because it strongly influenced the solution viscosity and conductivity. HNTs had relatively small impact on the growth of a crystalline morphology in PCL–HNT composites. The solvent mixture of chloroform : methanol was better for PLA‐based systems since PLA was found to have slightly higher crystallinity and larger enthalpy value indicating the improved structural orderness in the PLA polymer matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The dissolution characteristics of calcium sulfide and utilization as a precipitation agent in acidic wastewater effluent treatment

The dissolution characteristics of CaS in the presence of CO2 has been investigated by monitoring sulfide speciation, solution conductivity and pH during dissolution. The sulfide speciation associated with CaS dissolution was utilized for metal precipitation from acidic wastewater effluents. The mechanism involved in the dissolution process was observed to be pH-dependent, characterized by increased solution conductivity as the HS(-) species becomes dominant in solution in the form of the Ca(HS)2 complex. The replacement of HS(-) by CO3(2-) in the Ca(HS)2 complex triggered CaCO3 precipitation and H2S stripping and this was characterized by decreased solution pH and conductivity. The sulfide to total metal molar ratio was observed to have an effect on the pH and therefore sulfide speciation as well as extent of metal removal. The utilization of CaS in the treatment of acidic wastewater effluents demonstrated complete metal removal, with the potential of a pH-controlled selective metal removal and recovery.

Optical and Electrical Diagnostics of the Effects of Conductivity on Liquid Phase Electrical Discharge

The influence of solution conductivity on liquid phase pulsed electrical discharge was investigated by optical emission spectroscopy in a reactor with point-to-plane electrode geometry. The emission intensities of hydroxyl (OH) radical, hydrogen (H) radical, and oxygen (O) radical were measured using an emission intensity calibration method which used argon gas as a chemical actinometer. Control experiments showed that the addition of argon (Ar) bubbles did not disturb the electrical discharge. It was also found that the Ar emission peak at 750 nm is linearly related to the peaks of the other major species of interest (OH, H, and O) and that the slopes of these lines depend upon the solution conductivities. Therefore, the calibration method allows comparison of the radical generation rates in solutions of different conductivity. Hydrogen (H2), oxygen (O2), and hydrogen peroxide (H2O2) were measured using gas chromatography and spectrophotometric methods. The results showed that OH radicals and H2O2 decreased with increasing solution conductivity consistently with previous results. The intensities of O and H radicals and the generation rates of H2 and O2 were found to have extrema values at a conductivity of 150 μS/cm, and these results in combination with the electrical diagnostics (current waveform and overall power input) and images of the discharge channels imply changes in discharge properties at this conductivity due partly to power input changes from the spark gap. This work clearly demonstrates the close coupling of radical and molecular species formation in liquid phase electrical discharge.

Removal of toxic ions (chromate, arsenate, and perchlorate) using reverse osmosis, nanofiltration, and ultrafiltration membranes

Rejection characteristics of chromate, arsenate, and perchlorate were examined for one reverse osmosis (RO, LFC-1), two nanofiltration (NF, ESNA, and MX07), and one ultrafiltration (UF and GM) membranes that are commercially available. A bench-scale cross-flow flat-sheet filtration system was employed to determine the toxic ion rejection and the membrane flux. Both model and natural waters were used to prepare chromate, arsenate, and perchlorate solutions (approximately 100 μg L −1 for each anion) in mixtures in the presence of other salts (KCl, K 2SO 4, and CaCl 2); and at varying pH conditions (4, 6, 8, and 10) and solution conductivities (30, 60, and 115 mS m −1). The rejection of target ions by the membranes increases with increasing solution pH due to the increasingly negative membrane charge with synthetic model waters. Cr(VI), As(V), and ClO 4 - rejection follows the order LFC-1 (>90%) > MX07 (25–95%) ≅ ESNA (30–90%) > GM (3–47%) at all pH conditions. In contrast, the rejection of target ions by the membranes decreases with increasing solution conductivity due to the decreasingly negative membrane charge. Cr(VI), As(V), and ClO 4 - rejection follows the order CaCl 2 < KCl ≅ K 2SO 4 at constant pH and conductivity conditions for the NF and UF membranes tested. For natural waters the LFC-1 RO membrane with a small pore size (0.34 nm) had a significantly greater rejection for those target anions (>90%) excluding NO 3 - (71–74%) than the ESNA NF membrane (11–56%) with a relatively large pore size (0.44 nm), indicating that size exclusion is at least partially responsible for the rejection. The ratio of solute radius ( r i,s ) to effective membrane pore radius ( r p ) was employed to compare ion rejection. For all of the ions, the rejection is higher than 70% when the r i,s/r p ratio is greater than 0.4 for the LFC-1 membrane, while for di-valent ions ( CrO 4 2 - , SO 4 2 - , and HAsSO 4 2 - ) the rejection (38–56%) is fairly proportional to the r i,s / r p ratio (0.32–0.62) for the ESNA membrane.

Poly(methyl methacrylate)/silica nanocomposite fibers by electrospinning

AbstractUniform poly(methyl methacrylate) (PMMA)/silica nanocomposite fibers containing up to 20 wt % silica were prepared by electrospinning. The electrospun solutions were prepared by mixing a solution of PMMA in dimethyl formamide (DMF) with colloidal silica in methyl ethyl ketone (MEK). The average fiber diameter decreases from 2.49 μm to 1.69 μm when 20 wt % silica is incorporated as a result of considerably increased solution conductivity, although the solution viscosity increases significantly, which should result in opposite effect. Thinner fibers (down to 350 nm) can be obtained by changing DMF/MEK proportion and by the addition of an ammonium salt. Nano‐sized silica particles (10–40 nm) distributes homogeneously in the fibers, as revealed by transmission electron microscopy. Furthermore, the incorporation of silica nanoparticles can change the thermal properties and surface wettability of the fiber mats. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1211–1218, 2009