Effect of substrate surface on dewetting behavior and chain orientation of semicrystalline block copolymer thin films

Three symmetrical semicrystalline oxyethylene/oxybutylene block copolymers (EmBn) were spin-coated on different substrates including silicon, hydrophobically modified silicon, and mica. The effects of surface property on the dewetting behavior of EmBn thin films and the chain orientation of the crystalline block were investigated with atomic force microscopy and grazing incidence X-ray diffraction . The EmBn thin films on silicon exhibit an autophobic dewetting behavior, while ordinary dewetting occurs for the thin films on modified silicon. It was observed that the stems of the E crystals in the first half-polymer layer contacting the mica surface were parallel to the surface, in contrast to the perpendicular chain orientation of the other polymer layers and of the first half-polymer layer on silicon. This is attributed to the strong interaction between the E block and mica, verified by infrared spectra.     

Aggregation process of fine hematite particles suspension using xanthan gum in the presence of Fe(III)

Aggregation is an economical and widely existing method to in hematite mineral processing. In order to achieve the aggregation of hematite particles, high-efficiency agents are required. In this work, the xanthan gum (XG) and Fe³⁺ were used to explore its aggregation effect on the fine hematite particles. The settling and adsorption experiments were conducted on hematite with XG in the absence and presence of Fe³⁺. The results show that it is difficult to settle hematite with XG alone, and XG exhibits excellent performance with the mass ratio of 2/1 (XG/ FeCl₃) at pH 2–10 in the presence of Fe³⁺. Zeta potential measurements, Fourier transform infrared (FTIR), Microscope and X-ray photoelectron spectroscopy (XPS) analyses were performed to detect the underlying mechanism. The zeta potential, solution chemistry and FTIR analyses results show that the co-adsorption of XG, Fe(OH)₂⁺, Fe(OH)²⁺ and Fe³⁺ is found on hematite surface through specific and electrostatic adsorption, respectively, and the hematite surface is also covered by Fe(OH)_3(s) precipitation turned by Fe³⁺. XPS spectral investigations and microscope observations provide evidence in support of coordination interaction between ferric ions active sites and XG. In addition, the aggregation model of fine hematite particles suspension using XG in the presence of Fe³⁺ was drawn.     

Tailoring and investigation of surface chemical nature of virgin and ion beam modified muscovite mica

We report that the surface chemical properties of muscovite mica [KAl₂(Si₃Al)O₁₀(OH)₂] like important multi-elemental layered substrate can be precisely tailored by ion bombardment. The detailed X-ray photoelectron spectroscopic studies of a freshly cleaved as well as 12-keV Ar⁺ and N⁺ ion bombarded muscovite mica surfaces show immense changes of the surface composition due to preferential sputtering of different elements and the chemical reaction of implanted ions with the surface. We observe that the K atoms on the upper layer of mica surface are sputtered most during the N⁺ or Ar⁺ ions sputtering, and the negative aluminosilicate layer is exposed. Inactive Ar atoms are trapped, whereas chemically reactive N atoms form silicon nitride (Si₃N₄) and aluminum nitride (AlN) during implantation. On exposure to air after ion bombardment, the mica surface becomes more active to adsorb C than the virgin surface. The adsorbed C reacts with Si in the aluminosilicate layer and forms silicon carbide (SiC) for both Ar and N bombarded mica surfaces. Besides the surface chemical change, prolonged ion bombardment develops a periodic ripple like regular pattern on the surface.     

Needle-like IrO/Ag combined pH microelectrode

In this study, a combined pH microelectrode has been developed consisting of an indicator electrode made of IrO₂ prepared using the polymeric precursor method and deposited in a platinum microwire. This electrode was mounted inside a stainless steel needle, the external surface of which was painted with conductive silver ink which is used as reference electrode. This device was compared with a conventional glass electrode, and the results presented linear behavior in the pH range from 2.0 to 12.5, in Na⁺ and K⁺ solutions, exceeding glass electrodes in the alkaline range. The sensitivity was 56.9 ± 0.2 mV pH^? 1 and using ANOVA test we conclude that the electrode is not sensitive to the presence of alkaline cations such as Li⁺, Na⁺ or K⁺. Finally, the response time (t₉₅) was 4.9 to 9.0 s depending on the solution pH. The combined pH microelectrode can be used several times and, after three years, continues to have a response similar to that of a freshly produced one.     

Hydration forces between mica surfaces in electrolyte solutions

The forces between two molecularly smooth mica surfaces were measured over a range of concentrations in aqueous Li⁺, Na⁺, K⁺ and Cs⁺ chloride solutions. Deviations from DLVO forces in the form of additional short-range repulsive “Hydration” forces were observed only above some critical bulk concentration, which was different for each electrolyte. These observations are interpreted in terms of the corresponding ion exchange properties at the mica surface. “hydration” forces apparently arise when hydrated cations adsorbed on mica are prevented from desorbing as two interacting surfaces approach. dehydration of the cations leads to a repulsive hydration force. A simple site-binding model was successfully applied to describe the charging behavior of interacting mica surfaces . By subtraction of the DLVO-regulation theory from the total measured force the net hydration force was obtained for mica surfaces apparently fully covered with adsorbed cations. The magnitude of this extra force followed the series Na⁺ > Li⁺ > K⁺ > Cs⁺ and, in each case, could be described by a double-exponential decay.     

XPS investigations of the electrochemical double layer on silver in alkaline chloride solutions

The electrochemical double layer on Ag in alkaline NaCl solutions was examined ex situ with X-ray photoelectron spectroscopy (XPS). The specimens were removed from the electrolyte with hydrophobic surfaces and under potential control. The potential dependent surface concentrations of the adsorbed anions (Cl⁻, OH⁻), cations (Na⁺), the surface excess charge and the amount of adsorbed water were determined and compared to the results obtained for acidic NaCl solutions. The distinct differeness found between both electrolytes were discussed in terms of a specific adsorption of hydroxide ions in the basic Cl⁻-electrolyte; i.e., the OH⁻-surface concentration has to be considered for a proper determination of the cationic excess charge and the potential of zero charge. In addition, the initial stages of silver (1) oxide formation were examined with XPS.     

XPS- and AES-investigations of electron and ion beam induced effects on SK16 glass surfaces

Summary Electron beam induced effects in the near surface region of SK16 glass samples (44% SiO₂, 25% B₂O₃, 28% BaO, 3% other) have been studied using Auger electron spectroscopy (AES) with 3 keV primary electrons at different current densities (4.7 mAcm^–2–75 mAcm^–2). It was found that the SiO₂ and B₂O₃ constituents dissociate during electron bombardment to form binding structures which are characteristic for elemental Si and B, respectively. To investigate the influence of the ion beam irradiation on the binding structure, the glass samples were bombarded with Ar⁺ ions of different kinetic energies (0.5 keV–5 keV), followed by XPS analysis. In comparison to the XPS signal of a virgin SK16 surface from a sample fractured in situ under UHV conditions, the FWHM of the photoelectron peaks were found to increase with the bombarding ion energy. Subsequent Auger spectra revealed that the ion bombardment also caused a dissociation of the SiO₂ and B₂O₃ components. Depending on the ion energy, a constant ratio between elemental and oxidized binding form is obtained.     

Induction and Acceleration of Bonelike Apatite Formation on Tantalum Oxide Gel in Simulated Body Fluid

Untreated tantalum metal forms bonelike apatite layer on its surface in a simulated body fluid (SBF) after a long period. The apatite formation on the tantalum metal is significantly accelerated, when the metal was previously subjected to NaOH and heat treatments to form an amorphous sodium tantalate on its surface. The fast formation of the apatite on the NaOH- and heat-treated tantalum metal was explained as follows. The sodium tantalate on the surface of the metal releases the Na⁺ ion via exchange with H₃O⁺ ion in SBF to form a lot of Ta-OH groups on its surface. Thus formed Ta-OH groups induce the apatite nucleation and the released Na⁺ ion accelerates the apatite nucleation by increasing ionic activity product of the apatite in SBF due to increase in OH^– ion concentration. In the present study, in order to confirm this explanation, apatite formations on sodium tantalate gels with different Na/Ta atomic ratios, which were prepared by a sol-gel method were investigated. It was found that even Na₂O-free tantalum oxide gel forms the apatite on its surface in SBF. This proves that the Ta-OH groups abundant on the gel can induce the apatite nucleation. The apatite-forming ability of the gels increased with increasing Na/Ta atomic ratios of the gels. The sodium-containing tantalum oxide gels released the Na⁺ ion, the amount of which increased with increasing Na/Ta atomic ratios of the gels. The released Na⁺ ion gave an increase in pH of SBF. These results prove that the apatite nucleation induced by the Ta-OH groups is accelerated with the released Na⁺ ion by increasing ionic activity product of the apatite in SBF.     

Characterization of poly(vinylidene fluoride)/Na+‐MMT composites: An investigation into the β‐crystalline nucleation effect of Na+‐MMT

Poly(vinylidene fluoride)(PVDF)/Na⁺‐MMT composites have been successfully prepared utilizing sodium montmorillonite (Na⁺‐MMT) via N,N‐dimethylformamide (DMF) solution mixing. The dispersion of Na⁺‐MMT layers in composites were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The effect of adding Na⁺‐MMT on crystallization behavior of PVDF was specifically studied. The β‐crystalline nucleation effect of Na⁺‐MMT was investigated and confirmed by differential scanning calorimetry (DSC), XRD, and Fourier transform infrared (FTIR) results. The interaction between PVDF and the surface of Na⁺‐MMT layers in DMF solution was confirmed by UV‐Vis absorbency. The effect of adding Na⁺‐MMT on rheological and electrical properties of PVDF/Na⁺‐MMT composites were also determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 903–911, 2009     

Quantitative Auger depth profiling of LPCVD and PECVD silicon nitride films

Summary Thin silicon nitride films (100–210 nm) with refractive indices varying from 1.90 to 2.10 were deposited on silicon substrates by low pressure chemical vapour deposition (LPCVD) and plasma enhanced chemical vapour deposition (PECVD). Rutherford backscattering spectrometry (RBS), ellipsometry, surface profiling measurements and Auger electron spectroscopy (AES) in combination with Ar⁺ sputtering were used to characterize these films. We have found that the use of (p-p)heights of the Si LVV and N KLL Auger transitions in the first derivative of the energy distribution (dN(E)/dE) leads to an accurate determination of the silicon nitride composition in Auger depth profiles over a wide range of atomic Si/N ratios. Moreover, we have shown that the Si KLL Auger transition, generally considered to be a better probe than the low energy Si LVV Auger transition in determining the chemical composition of silicon nitride layers, leads to deviating results.

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Quantitative Auger-Tiefenprofilanalyse von LPCVD- und PECVD-Siliciumnitridfilmen

     

What causes extended layering of ionic liquids on the mica surface?

Extended layering of ionic liquids (ILs) on the mica surface has been reported by several groups previously and it is generally accepted that the electrostatic interaction at the IL/mica interface is critical to the observed extended layering. Here we report that, indeed, water adsorption on the mica surface is the key to the extended layering of ionic liquids. The atomic force microscopy (AFM), attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR) and contact angle (CA) results show that ionic liquids form extended layering on a mica surface under ambient conditions when water is adsorbed on the mica surface under such conditions. However, when airborne hydrocarbon contaminants replace the water on the mica surface at the elevated temperatures, instead of layering, ionic liquids exhibit droplet structure, i.e., dewetting. Based on the experimental results, we propose that water enables ion exchange between K+ and the cations of ILs on the mica surface and thus triggers the ordered packing of cations/anions in ILs, resulting in extended layering.     

Interaction of sodium and potassium ions withκ-carrageenan

Summary NMR and potentiometric methods revealed at least two types of interactions of Na⁺ and K⁺ ions with -carrageenan, viz., Coulombic interaction with polysaccharide sulfate groups, and a coordination one, leading, in the case of the Na⁺ ions, to formation of nonstoichiometric complexes. The absence of any correlation between the coordination binding density of the cations and their promoting effect on gelation process was demonstrated.     

Charge storage mechanism of copper hexacyanoferrate nanocubes for supercapacitors

The widely accepted theory concerning the electrochemical energy storage mechanism of copper hexacyanoferrate (CuHCF) for supercapacitors is that CuHCF stores charge by the reversible redox processes of Fe³⁺/Fe²⁺ couple and Cu cations are electrochemically inactive. In this work, CuHCF nanocubes (CuHCF-NC) were synthesized in the presence of potassium citrate and its electrochemical properties were tentatively studied in 1 mol/L Na₂SO₄ aqueous electrolyte. Good supercapacitive performance was exhibited. The combined analyses of cyclic voltammogram (CV) and X-ray photoelectron spectroscopy (XPS) disclosed that the CuHCF nanocubes underwent the redox reactions of Fe³⁺/Fe²⁺ and Cu²⁺/Cu⁺ couples to store charges. The Cu²⁺/Cu⁺ redox couple was activated due to the strong coordination interaction between the carboxylate groups of citrate ions and surface Cu cations.     

Sodium Ion-Selective Chalcogenide Glass Electrodes

Abstract

Analytical characteristics and sensing mechanism of sodium ion-selective electrodes based on NaCl-Ga₂S₃-GeS₂ glasses have been investigated. Chalcogenide glass electrodes containing 10 mol.% NaCl in the membrane showed near-Nernstian response in the concentration range from 10-³ to 1 M sodium nitrate solution. These sensors were superior to the conventional pNa oxide glass electrodes in selectivity in the presence of hydrogen ions and in Na⁺ ion sensitivity in fluoride media. Prolonged solution treatment for several days reduces, however, the detection limit of the sensors and the slope of the electrode response. Ionic processes at the membrane surface have been investigated using XPS technique and ²²Na tracer measurements. It was shown that sodium ion-exchange governed Na⁺ ion response of chalcogenide     

In situ XPS and SIMS analysis of O2+ beam‐induced silicon oxidation

The chemical composition variation of silicon under 4 keV O₂⁺ ion beam bombardment at different incident angles was studied by in situ small‐area XPS. The changes in secondary ion profile (³⁰Si⁺, ⁴⁴SiO⁺, ⁵⁶Si₂⁺, ⁶⁰SiO₂⁺) during oxygen ion beam bombardment also have been monitored. We present a direct correlation of the changes in secondary ion depth profile with surface composition during sputtering. Evolution of the secondary ion profile obtained from SIMS shows similar trends with variation of oxygen concentration in the crater surface measured by XPS. It is shown that when the oxygen ion beam incidence angle is < 40° silicon dioxide is the dominant species on the crater surface and the matrix ion species ratio (MISR) value for ⁴⁴SiO⁺/⁵⁶Si₂⁺ is higher than for ³⁰Si⁺/⁵⁶Si₂⁺. For incidence angles of >40°, the formation of sub‐oxide is favoured and thus the MISR value for ⁴⁴SiO⁺/⁵⁶Si₂⁺ is lower than for ³⁰Si⁺/⁵⁶Si₂. At 40° bombardment there are similar amounts of SiO₂ and sub‐oxides present on the crater surface and the MISR values for ⁴⁴SiO⁺/⁵⁶Si₂⁺ and ³⁰Si⁺/⁵⁶Si₂⁺ are also similar. Copyright © 2004 John Wiley & Sons, Ltd.     

Monovalent Cation–Phenolic Crystals with pH-Driven Reversible Crystal Transformation

The conversion of renewable plant polyphenol to advanced materials with tailorable properties and various functions is desirable and challenging. In this work, monovalent cation-phenolic crystals contained K⁺ or Na⁺ ions were synthesized by using plant polyphenol as an organic source in alkaline solution. The crystal structure was resolved, showing a laminar crystal structure with M⁺ as connecting nodes. The morphologies (e.g., rod-like and spindle-shaped) and chemical compositions of crystals could be tuned by changing the cations. Interestingly, these polymer crystals exhibited a pH-driven reversible crystal transformation. They transformed into their protonated crystalline form under acidic conditions (e.g., pH 2) and went back to the cation-bound crystalline form in alkaline solutions. Furthermore, the crystals proved excellent antioxidants and heavy metal ion adsorbents.     

Borazon-gate pH-sensitive field effect transistor

A borazon-gate ISFET is used as a pH sensor. Boron nitride was deposited by the reactive-pulse plasma method and electron diffraction served for membrane identification. The borazon-gate sensors responded linearly to pH in the range 1.8–10; the slope was about 52 mV pH^?1. Selectivity for H⁺ ions over K⁺, Na⁺ or Ca²⁺ ions was better than that of silicon nitride-gate ISFETs.     

Adsorption of polymers with crown ether substituents on muscovite mica

Ultrahigh specific surface area muscovite with different ions at the surface (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, Sr²⁺, Ba²⁺, Cu²⁺) was treated with aqueous solutions of low molecular weight crown ethers and polymers with crown ether substituents. The adsorption was assessed by UV analysis of the supernatant solution, and with TGA and IR spectroscopy of the mica solids. In contrast to other layered silicates, the low molecular weight crown ethers show no affinity to any of the muscovite surfaces. The polymers can adsorb, however, depending on the type of surface cation. The results indicate that at least some of the crown ether moieties are complexed to surface cations and that the diameter of the ions at the surface plays an important role in the adsorption process.     

Studies on the mechanisms of gelation of kappa-carrageenan and agarose

It has been established that hydrogen bonds control both gelation and helix formation completely in the case of agarose and partially in the case of kappa-carrageenan, the major role belonging in the latter case to the interactions of a polysaccharide with metal ions. Na⁺ and K⁺ ions form contact ion pairs with sulphate groups of kappa-carrageenan. It is supposed that an increase in the number of contact ion pairs together with association of macromolecules having unordered conformation, a decrease in the second virial coefficient, and a decrease in the refraction index increment (i.e., an increase in the solvation degree of dissolved particles) is a necessary condition for forming the kappa-carrageenan gel netwórk. A sufficient condition of kappa-carrageenan gelation is the intermolecular coordination binding of ions such as K⁺ ions, promoting gelation. The coil-to-helix transition of the polysaccharide is controlled by shielding the charge of kappa-carrageenan-sulphate groups. Hydrophobic interactions proved to be unessential for gelation of either agarose or kappa-carrageenan.     

Combined application of pair potentials and the MM2 force field for the modeling of ionophores

Complexes of alkali and alkaline earth cations with organic compounds are modeled by describing ionligand interaction energies with pair potentials and intraligand as well as interligand energies with the MM2 potential. New pair potentials for the interaction of Li⁺, Na⁺, K⁺, Mg²⁺, and Ca²⁺ ions are derived on the basis of 30,000 ab initio interaction energy values with 70 selected model ligand molecules. Various problems of the combination of these two basically different potentials are discussed. An application for the K⁺ complex of 18-crown-6 is presented. For more flexible ligands the introduction of three-body correction terms of the pair potentials seems necessary.