NaI Salt Research Articles

Effect of Sodium Iodide on Structural, Electrical and Optical Properties of Polyethylene Oxide/ Carboxymethyl Cellulose Blends

The production of highly potential Solid Polymer Electrolyte (SPE) materials has been the subject of extensive research. Due to their high flexibility, superior processability and enhanced resistance to electrodes during the charging/discharging process, they found to exhibit wide applications when compared to liquid or gel. In the present study, SPE films with 30/70 composition of Polyethylene oxide/Carboxymethyl cellulose blend, doped with Sodium Iodide (NaI) were prepared using a simple solution cast technique. The optical properties of the prepared samples were studied by UV–Vis spectroscopy technique and the results show that, the energy band gap decreases with the increase of salt concentration which is due to the enhancement of amorphous nature with the concentration of salt and is as evidenced from X-Ray diffraction studies. The electrical properties of the samples were studied using impedance analyser. The dielectric constant of the prepared samples decreases exponentially with frequency of applied electric field. In addition, the AC conductivity of the blend was found to increase with increase in salt concentration and the maximum conductivity was observed for 0.03% NaI salt doped Polyethylene oxide/Carboxymethyl cellulose blend. Thus, the said samples can be used in the preparation of SPE’s

Ultra-trace SERS detection of cocaine and heroin using bimetallic gold–silver nanostars (BGNS-Ag)

A rapid, in-field, and reliable method for the detection of illegal drugs of abuse in biological fluids without any sample pretreatment would potentially be helpful for law enforcement, drug control officials, and public healthcare. In this study, we presented a cost-effective and highly reproducible solution-based surface-enhanced Raman scattering (SERS) platform utilizing a portable Raman instrument for fast sensitive SERS detection of illegal drugs, such as cocaine, and heroin in human urine without any sample preprocessing. The SERS platform was constructed for the first time by combining the superior SERS enhancement properties of bimetallic silver-coated gold nanostars (BGNS-Ag) and the advantages of suitable alkaline metal salts such as NaI for SERS signal amplification. The effects of the silver thickness of BGNS-Ag and alkaline salts on the SERS performance were investigated in detail; we observed that the maximum SERS enhancement was obtained for BGNS-Ag with the maximum silver thickness (54 ± 5 nm) in presence of NaI salt. Our SERS platform shows ultra-high sensitivity of cocaine and heroin with a limit of detection (LOD) as low as 10 pg/mL for cocaine and 100 pg/mL for heroin, which was 100 times lower than that of the traditional silver nanoparticle-based illegal drug detection. As a demonstration, the platform was further applied to detect cocaine and heroin spiked in human urine without any sample preprocessing achieving a LOD of 100 pg/mL for cocaine and 1 ng/mL for heroin. Overall, our SERS detection platform shows potential for rapid, onsite, ultra-low-cost portable applications for trace detection of illegal drugs and biomarkers.

Studies on structural and electrical properties of NaI doped PEO/CMC blend solid polymer electrolyte

Solid polymer blend electrolyte (SPE) films of Polyethylene oxide(PEO)/Carboxymethyl cellulose (NaCMC) doped with Sodium iodide (NaI), were prepared by solution cast method and their structural, optical and electrical properties were investigated using X-Ray diffraction, Fourier transform infrared spectroscopy, UV–Vis spectrophotometer and Electrical impedance analyser respectively. X-Ray diffraction spectra indicate that, deformation occurred in the structure of the blend followed by doping with NaI salt. The variation in intensity and shifting of characteristic bands in FTIR spectra provides the evidence for formation of complex due to the interaction occurred in the blend with the dopant. Optical energy band gap decreases in the blend samples upon doping and is confirmed by UV–Vis spectrophotometer analysis. Increase of dielectric constant and loss upon doping, exhibits usual behaviour of the polymer electrolytes. An increase in AC conductivity is observed upon doping and maximum conductivity of 9.41 × 10−3 Scm−1 is obtained for 10/90 sample doped with 0.03% Sodium iodide and DC conductivity for the same sample at room temperature is 1.05 × 10–2 Scm−1. In addition, I-T studies confirm the conductivity exhibited by the sample as due to ions and I-V studies show electrochemical stability in the range of good working potential. From the results obtained, it can be inferred that, the prepared sample can be used as polymer electrolytes in the manufacturing of energy storage devices.

Ionic conductivity enhancement of PVA: carboxymethyl cellulose poly-blend electrolyte films through the doping of NaI salt

In this paper, we report the effect of doping sodium iodide (NaI) salt into a polymer blend matrix of sodium carboxymethyl cellulose (NaCMC) and poly(vinyl alcohol) (PVA). Solution casting approach was used to prepare solid polymer electrolyte (SPE) films. The films were characterized by Fourier-transform infrared spectroscopy (FTIR), X-Ray diffraction (XRD), electrical impedance spectroscopy, thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). XRD showed that NaI incorporation decreased the crystallinity of NaCMC/PVA-based SPE. FTIR technique confirmed the complexation of salt with polymer matrix due to the formation of the coordination bond between Na+ and –OH group and hydrogen bond between I− and –CH group. The sample with 30 wt% NaI showed the highest conductivity of 2.52 × 10–3 S cm−1, strongly influenced by the highest charge concentration (n), not its mobility (μ). DSC analysis revealed an increase in glass transition temperature ({T}_{g}) with increasing salt content. TGA studies showed a decrease in thermal stability with salt inclusion. The transference number was found to be 0.99 for the highest conducting sample showing the primary charge carriers are ions. The highest conducting sample exhibited a mechanical strength of 15.42 MPa at room temperature, and it has been used to fabricate a battery to evaluate its suitability in energy storage devices.Graphical abstractGraphical abstract created with https://biorender.com.

Structural and electrical properties of polyvinyl alcohol (PVA):Methyl cellulose (MC) based solid polymer blend electrolytes inserted with sodium iodide (NaI) salt

This paper studies the structural and electrical properties of solid polymer blend electrolytes based on polyvinyl alcohol (PVA) and methylcellulose (MC) incorporated with sodium iodide (NaI). The polymer electrolyte films were assembled through a solution casting technique. The host matrix, which is doped with different NaI salt concentrations between 10 and 50 wt%, utilizes the most amorphous blend compositions (60 wt% Polyvinyl alcohol and 40 wt% methylcellulose). The structural behaviour of the electrolyte films was examined utilizing X-ray diffraction (XRD) and Fourier transformation infrared (FTIR) techniques. The semi crystalline nature of PVA:MC with inserted NaI was derived from the X-ray diffraction studies, while the XRD analysis suggests that the highest ion conductive sample displays the minimum crystalline nature. The interaction between polymer blends and inserted salt was conceived from the FTIR investigation. Shifting of peaks and variation in the intensity of FTIR bands was detected. To investigate the structural properties and calculate the degree of crystallinity of the films, the (XRD) technique was employed, while electrical impedance spectroscopy (EIS) was utilized for studying the conductivity of the samples. In order to comprehend all of the electrical properties of the ion-conducting systems, the EIS outcome of each electrolyte was matched with Equivalent Electrical Circuits ( EEC) s. Ion transport parameters including mobility, carrier density and diffusion are well assessed for the samples and the dielectric properties were compared with the conductivity measurement. At lower frequencies, the dielectric constant was elevated and dielectric loss was detected. Loss tangent and electric modulus plots were used to study the relaxation nature of the samples. The highest ambient temperature conductivity of PVA loaded 50 wt% of NaI was determined to be 1.53 × 10 −5 S/cm. The loss tangent relaxation peak shifts towards high-frequency side which indicates the decrease of relaxation time and faster ion dynamics.

Chitosan as a paradigm for biopolymer electrolytes in solid-state dye-sensitised solar cells

Biopolymers are among the most promising electrolyte hosts for different electrochemical devices in the energy conversion and storage fields. In this work, the potential of chitosan as a biopolymer laden with NaI salt is explored and applied as solid polymer electrolyte for dye sensitised solar cells. The chitosan-NaI electrolyte is successfully prepared via a simple and upscalable solution casting technique. Infrared spectroscopy analysis highlights interactions between chitosan and NaI, that weaken the semi-crystalline domains of chitosan and favour the conduction of the redox shuttle ions between cell electrodes. At room temperature, the best ionic conductivity was obtained for the samples laden with NaI 30 wt%, with values equal to 1.11 × 10−4 S cm−1. Na+ transference number determination indicates that only 0.9% of the ionic conductivity is determined by these cations, thus highlighting that I− anions represent the active species in the newly proposed solid-state electrolyte. This result is highly desired considering that these anions are those responsible for the regeneration of oxidized dye molecules in the cell and, overall, for the cell efficiency. Current-voltage measurement of solid-state photovoltaic devices under simulated sunlight led to a reproducible and stable power conversion efficiency of 0.06%, along with a short-circuit current density of 0.32 mA cm−2, an open circuit voltage of 0.7 V and a fill factor 0.3.

Structural and impedance analysis of PAN-based Na+ ion conducting gel polymer electrolytes for energy storage device application

The polymer electrolytes are used in energy storage devices. Sodium ion-conducting gel polymer electrolytes based on Polyacrylonitrile (PAN) complexed with an alkali salt (NaI) and Ethylene carbonate (EC) and Dimethylformamide (DMF) as plasticizing solvents were prepared from solution cast method. The developed membrane were dimensionally stable. Structural, Impedance and conductivity studies were carried on to the prepared samples. The electrical studies were performed using lab-made conductivity setup. The complex formation between NaI salt and PAN had been confirmed by XRD studies and revealed the amorphous behaviour of the prepared membranes. The conductivity and bulk resistance of gel polymer electrolytes were measured by impedance analysis by changing the composition concentration of PAN-NaI. The maximum conductivity (1x10-3 S/cm) was observed for PAN: NaI (70:30) at temperature 373 K. The conductivity dependence temperature of these mebranes obeys the principle of Arrhenius.

Augmentation of dye-sensitized solar cell photovoltaic conversion efficiency via incorporation of terpolymer Poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) based gel polymer electrolytes

A dye-sensitized solar cell (DSSC) is the alternative photovoltaic technology for the replacement of the standard photovoltaic liquid electrolyte-dependent cell. Gel polymer electrolyte (GPE) was used in this research to replace the volatile liquid electrolyte. This GPE has been developed using terpolymer type Poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) P(VB-co-VA-co-VAc), iodine (I2), sodium iodide (NaI), and ethanol. The findings from X-ray diffraction (XRD) showed the effect of NaI on the crystalline content of the electrolyte systems. Samples showed higher conductivity with a lower degree of crystallinity. Differential scanning calorimetry (DSC) analysis revealed the slight decrease in melting temperature (Tm) upon addition of NaI salts. The thermogravimetric analysis (TGA) showed that GPE ′s thermal stability decreases as NaI salt content increases. Fourier-transform infrared (FTIR) results indicated that P(VB-co-VA-co-VAc) interacted with NaI. The highest room temperature ionic conductivity of 3.22 × 10−3 S cm−1 by the sample with 30 wt % NaI. Temperature-dependent findings showed that all GPE samples adhere to the Arrhenius equation in the temperature range from 303 K to 373K and found the lowest activation energy obtained by the sample with 30 wt % NaI as 0.066 eV. Dielectric and modulus properties of all samples have been studied. DSSC fabricated using the electrolyte containing 30 wt% NaI has achieved the highest conversion efficiency of 4.01% with maximum JSC value of 12.52 mA cm−2, VOC of 0.61 V, and fill factor (FF) of 51.8%.

Consolidation of ion promoters into quasi solid-state (QSS) polymer electrolytes for dye-sensitized solar cells (DSSCs)

Enhanced quasi solid-state (QSS) polymer electrolytes were developed by consolidating dissolved polyacrylonitrile (PAN) in a binary organic solvent of ethylene carbonate-propylene carbonate (EC-PC) with ion promoters such as 1-methyl-3-propylimidazolium iodide (MPII), sodium iodide (NaI) salt, and Iodine (I2). In this work, the concentration of I2 was varied to one-twentieth, one-fifteenth, one-tenth, one-fifth, and equal of the total weight of the NaI salt used. The purpose of this study is to investigate the dependence of dye-sensitized solar cells (DSSCs) performance on the concentration of I2. Fourier-transform infrared (FTIR) spectroscopy study confirmed that there is a complexation occurred between all materials used. The electrolyte consists of I2 with one-tenth of the weight of the NaI salt (I1/10 electrolyte) has achieved the highest ionic conductivity of 8.70 × 10–3 S cm-1 at ambient temperature. From the current density-voltage (J-V) study, DSSC based I1/10 electrolyte has achieved the best photovoltaic efficiency of 6.47%.

Sulfolane-Induced Supercharging of Electrosprayed Salt Clusters: An Experimental/Computational Perspective.

It is well-known that supercharging agents (SCAs) such as sulfolane enhance the electrospray ionization (ESI) charge states of proteins, although the mechanistic origins of this effect remain contentious. Only very few studies have explored SCA effects on analytes other than proteins or peptides. This work examines how sulfolane affects electrosprayed NaI salt clusters. Such alkali metal halide clusters have played a key role for earlier ESI mechanistic studies, making them interesting targets for supercharging investigations. ESI of aqueous NaI solutions predominantly generated singly charged [NanI(n-1)]+ clusters. The addition of sulfolane resulted in abundant doubly charged [NanI(n-2)Sulfolanes]2+ species. These experimental data for the first time demonstrate that electrosprayed salt clusters can undergo supercharging. Molecular dynamics (MD) simulations of aqueous ESI nanodroplets containing Na+/I- with and without sulfolane were conducted to obtain atomistic insights into the supercharging mechanism. The simulations produced [NanIi]z+ and [NanIiSulfolanes]z+ clusters similar to those observed experimentally. The MD trajectories demonstrated that these clusters were released into the gas phase upon droplet evaporation to dryness, in line with the charged residue model. Sulfolane was found to evaporate much more slowly than water. This slow evaporation, in conjunction with the large dipole moment of sulfolane, resulted in electrostatic stabilization of the shrinking ESI droplets and the final clusters. Hence, charge-dipole stabilization causes the sulfolane-containing droplets and clusters to retain more charge, thereby providing the mechanistic foundation of salt cluster supercharging.

Polyacrylonitrile–poly(1‐vinyl pyrrolidone‐co‐vinyl acetate) blend based gel polymer electrolytes incorporated with sodium iodide salt for dye‐sensitized solar cell applications

ABSTRACTNew gel polymer electrolytes (GPEs) were prepared via the blending of a polyacrylonitrile polymer and a poly(1‐vinyl pyrrolidone‐co‐vinyl acetate) copolymer. The sodium iodide (NaI) salt concentration was varied for each GPE sample. From ionic conductivity (σ) studies, we observed that the sample with a 40 wt % NaI salt content (N40) showed the highest σ of 3.54 × 10−3 ± 0.05 S/cm at room temperature, and all of the GPE samples obeyed Arrhenius behavior. The dielectric properties of the GPE samples were also analyzed to study the electrical polarization of the materials. The developed GPE samples were also characterized with X‐ray diffraction and Fourier transform infrared spectroscopy. We also then used the developed GPE samples for the fabrication of dye‐sensitized solar cells by sandwiching them between a photoanode and Pt counter electrode for photovoltaic studies. The highest photovoltaic performance was achieved by N40, with an efficiency of 3.04%. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47810.

Effect of different imidazolium-based ionic liquids on gel polymer electrolytes for dye-sensitized solar cells

Host polymer electrolytes are prepared using poly(ethylene oxide) (PEO) as a polymer, ethylene carbonate (EC) and propylene carbonate (PC) as solvents, sodium iodide (NaI) as salt, and iodine (I2) and with either one of the ionic liquids (ILs) which are 1-methyl-3-propylimidazolium iodide (MPII), 1-butyl-3-methylimidozium (BMII), and 1-hexyl-3-methylimidozium iodide (HMII) in each gel polymer electrolyte. The ionic conductivity of the gel polymer electrolytes (GPEs) was measured by electrochemical impedance spectrometer (EIS). The ionic conductivity of GPEs increased with the presence of ionic liquids (ILs). At room temperature, the dielectric behaviors of the GPEs were studied. The highest ionic conductivity of 9.41 mS cm−1 is achieved after addition of MPII ionic liquid. Meanwhile, Fourier-transform infrared and X-ray diffraction studies confirm complexation between PEO polymer, NaI salt, and ionic liquids (MPII, BMII, and HMII). Dye-sensitized solar cells (DSSCs) were fabricated using polymer electrolytes and studied under Sun simulator. The DSSC using MPII ionic liquid shows the highest efficiency of 9.35%.

Conductivity, dielectric studies and structural properties of P(VA-co-PE) and its application in dye sensitized solar cell

Abstract Poly(vinyl alcohol-co-ethylene), P(VA-co-PE) gel polymer electrolytes (GPEs) with sodium iodide (NaI) as a dopant salt was synthesized and investigated. Electrolytes containing different concentrations of NaI salt were studied using AC impedance spectroscopy, FTIR spectroscopy, and XRD spectroscopy. The results from dielectric studies reveal both the real part and imaginary part of complex permittivity decrease with increasing frequency. An opposite trend was observed when the temperatures of the samples were increased. Besides, the dispersion relation from the modulus studies confirmed that ionic conductivity is dominant in the GPE samples. Results from temperature studies reveal that all GPE samples conform the Arrhenius equation in the temperature range of 303 K to 373 K. The sample with 40% of NaI exhibits the highest ionic conductivity of 2.266 mS cm−1 with the activation energy of 0.16808 eV. Furthermore, FTIR studies proved the complexation between P(VA-co-PE) and NaI. The crystallinity of the samples was shown to be increasing with the increasing concentration of NaI salt via XRD results. Finally, DSSCs were assembled using the polymer electrolyte and used for photovoltaic studies. The best performance of DSSC was obtained with the energy conversion efficiency of 3.32% using the GPE sample with 40% NaI.

First principle studies on electronic structure and charge density of potato starch

The electronic and chemical bonding properties of biomaterial potato starch within the density functional theory are presented in this paper, with the aim to be used in electrochemical devices and biomedical applications. In the density of states and projected density of states analysis, the energy difference between the highest occupied molecular orbital and lowest unoccupied molecular orbital is reduced by 2.9 eV, which exhibits the semi-conducting behaviour of modified potato starch in the presence of NaI salt. Calculated charge density predicts the bonding properties and crystal orbital overlap population analysis exhibits the increase of amorphous nature and ionic conductivity due to sodium ion concentration. In this theoretical study, different behaviours of modified potato starch are clearly seen in the presence of NaI salt.

Free energetics of carbon nanotube association in aqueous inorganic NaI salt solutions: Temperature effects using all-atom molecular dynamics simulations.

In this study, we examine the temperature dependence of free energetics of nanotube association using graphical processing unit-enabled all-atom molecular dynamics simulations (FEN ZI) with two (10,10) single-walled carbon nanotubes in 3 m NaI aqueous salt solution. Results suggest that the free energy, enthalpy and entropy changes for the association process are all reduced at the high temperature, in agreement with previous investigations using other hydrophobes. Via the decomposition of free energy into individual components, we found that solvent contribution (including water, anion, and cation contributions) is correlated with the spatial distribution of the corresponding species and is influenced distinctly by the temperature. We studied the spatial distribution and the structure of the solvent in different regions: intertube, intratube and the bulk solvent. By calculating the fluctuation of coarse-grained tube-solvent surfaces, we found that tube-water interfacial fluctuation exhibits the strongest temperature dependence. By taking ions to be a solvent-like medium in the absence of water, tube-anion interfacial fluctuation shows similar but weaker dependence on temperature, while tube-cation interfacial fluctuation shows no dependence in general. These characteristics are discussed via the malleability of their corresponding solvation shells relative to the nanotube surface. Hydrogen bonding profiles and tetrahedrality of water arrangement are also computed to compare the structure of solvent in the solvent bulk and intertube region. The hydrophobic confinement induces a relatively lower concentration environment in the intertube region, therefore causing different intertube solvent structures which depend on the tube separation. This study is relevant in the continuing discourse on hydrophobic interactions (as they impact generally a broad class of phenomena in biology, biochemistry, and materials science and soft condensed matter research), and interpretations of hydrophobicity in terms of alternative but parallel signatures such as interfacial fluctuations, dewetting transitions, and enhanced fluctuation probabilities at interfaces.

An optimized poly(vinylidene fluoride-hexafluoropropylene)–NaI gel polymer electrolyte and its application in natural dye sensitized solar cells

Gel type polymer electrolytes with PVDF-HFP as polymer host, NaI salt and EC/PC as plasticizers have been prepared and optimized for use in a dye sensitized solar cell (DSSC). The polymer electrolyte containing 48wt. % (PVDF-HFP)–32wt. % NaI–20wt. % (EC/PC) exhibits the highest room temperature conductivity of 1.53×10−4 S cm−1. This electrolyte has been used in the fabrication of a DSSC with the configuration FTO/TiO2/natural dye/electrolyte/Pt/FTO. The natural dyes used anthocyanin and chlorophyll were solvent extracted from black-rice and pandanus amaryllifolius leaves respectively. UV-vis absorption spectra of anthocyanin, chlorophyll and the mixture of anthocyanin and chlorophyll in the volume ratio 1:1 were recorded. The anthocyanin shows an absorption peak at 532nm. In the same region chlorophyll absorption shows a peak at 536nm and also has a prominant peak at 665nm. On mixing anthocyanin and chlorophyll two prominant peaks are observed at 536 and 665nm. The DSSC containing the dye mixture exhibits the best performance with a short-circuit current density of 2.63mAcm−2, open-circuit voltage of 0.47V, fill factor of 0.58 and the highest photo-conversion efficiency of 0.72% under the illumination of 100mW cm−2 white light. Under illumination of lower light intensity of 60mW cm−2 and 30mW cm−2, the fill factor enhanced from 0.58 to 0.59 and 0.60 and the photo-conversion efficiency increased from 0.72% to 1.11% and 1.85% respectively.

Structural, thermal, and electrical studies of sodium iodide (NaI)-doped hydroxypropyl methylcellulose (HPMC) polymer electrolyte films

Solid polymer electrolyte films based on hydroxypropyl methylcellulose (HPMC) complexed with sodium iodide (NaI) were prepared using solution cast method. The dissolution of the salt into the polymer host and the structural properties of pure and complexed HPMC polymer electrolyte films were confirmed by X-ray diffraction (XRD) studies. XRD results revealed that the amorphous domains of HPMC polymer matrix were increased with increase in NaI salt concentration. The degree of crystallinity was found to be high in pure HPMC samples. The thermal properties were studied using differential scanning calorimetry (DSC). DSC results revealed that the presence of NaI in the polymer matrix increases the melting temperature; however, it is observed that fusion heat is high for pure HPMC films. The variation of film morphology was examined by scanning electron microscopy. Fourier transform infrared spectral studies revealed vibrational changes that occurred due to the effect of dopant salt in the polymer. Direct current conductivity was measured in the temperature range of 313–383 K. The magnitude of electrical conductivity was found to increase with the increase in salt and temperature concentration. The data on the activation energy regions (regions I and II) indicated the dominance of ion-type charge transport in these polymer electrolyte films. The composition HPMC:NaI (5:4) is found to exhibit the least crystallinity and the highest conductivity.

Molecular mechanisms of salt effects on carbon nanotube dispersions in an organic solvent (N-methyl-2-pyrrolidone)

We consider the effects of salt (sodium iodide) on pristine carbon nanotube (CNT) dispersions in an organic solvent, N-methyl-2-pyrrolidone (NMP). We investigate the molecular-scale mechanisms of ion interactions with the nanotube surface and we show how the microscopic ion-surface interactions affect the stability of CNT dispersions in NMP. In our study we use a combination of fully atomistic Molecular Dynamics simulations of sodium and iodide ions at the CNT-NMP interface with direct experiments on the CNT dispersions. In the experiments we analyze the effects of salt on the stability of the dispersions by photoluminescence (PL) and optical absorption spectroscopy of the samples as well as by visual inspection. By fully atomistic Molecular Dynamics simulations we investigate the molecular-scale mechanisms of sodium and iodide ion interactions with the nanotube surface. Our simulations reveal that both ions are depleted from the CNT surface in the CNT-NMP dispersions mainly due to the two reasons: (1) there is a high energy penalty for the ion partial desolvation at the CNT surface; (2) NMP molecules form a dense solvation layer at the CNT surface that prevents ions to come close to the CNT surface. As a result, an increase of the salt concentration increases the osmotic stress in the CNT-NMP system and, thus, decreases the stability of the CNT dispersions in NMP. Direct experiments confirm the simulation results: addition of NaI salt into the NMP dispersions of pristine CNTs leads to precipitation of CNTs (bundle formation) even at very small salt concentration (∼10 -3 mol L -1). In line with the simulation predictions, the effect increases with the increase of the salt concentration. Overall, our results show that dissolved salt ions have strong effects on the stability of CNT dispersions. Therefore, it is possible to stimulate the bundle formation in the CNT-NMP dispersions and regulate the overall concentration of nanotubes in the dispersions by changing the NaI concentration in the solvent.

Role of spatial ionic distribution on the energetics of hydrophobic assembly and properties of the water/hydrophobe interface

We present results from all-atom molecular dynamics simulations of large-scale hydrophobic plates solvated in NaCl and NaI salt solutions. As observed in studies of ions at the air-water interface, the density of iodide near the water-plate interface is significantly enhanced relative to chloride and in the bulk. This allows for the partial hydration of iodide while chloride remains more fully hydrated. In 1 M solutions, iodide directly pushes the hydrophobes together (contributing -2.51 kcal mol(-1)) to the PMF. Chloride, however, strengthens the water-induced contribution to the PMF by ~-2.84 kcal mol(-1). These observations are enhanced in 3 M solutions, consistent with the increased ion density in the vicinity of the hydrophobes. The different salt solutions influence changes in the critical hydrophobe separation distance and characteristic wetting/dewetting transitions. These differences are largely influenced by the ion-specific expulsion of iodide from bulk water. Results of this study are of general interest to the study of ions at interfaces and may lend insight to the mechanisms underlying the Hofmeister series.

Salting out in organic solvents: a new route to carbon nanotube bundle engineering

In this study we investigate salt effects on bundle formation of carbon nanotubes (CNTs) dispersed in an organic solvent, N-methyl-2-pyrrolidone (NMP). Addition of NaI salt leads to self-assembly of CNTs into well-recognizable bundles. It is possible to control the size of the CNT bundles by varying the salt concentration.