Intercalation Levels Research Articles

Membrane potential and impedance studies of polyaniline composite membranes: Effects of membrane morphology

Electronic and ionic transport characteristics of PANI composite porous membranes are presented in this study. Microporous cellulose ester membranes were modified by depositing polyaniline (PANI) either as a surface layer or as a layer on the pore walls of the base membrane. Various in situ chemical oxidative polymerization techniques were used that yielded distinctive PANI deposition sites in the base membranes. PANI intercalation levels in the composite membranes were evaluated using gravimetric method whereas the deposition site was characterized by scanning electron microscopy (SEM). Among the employed polymerization techniques, diaphragmatic polymerization of aniline using a two-compartment cell deposited PANI inside the membrane bulk with PANI content as high as 50% (w/w). Other techniques including solution-phase and vapor-phase polymerizations deposited PANI on the membrane surface with little in-bulk deposition. Electrochemical characterization of the membranes was conducted by electrochemical impedance spectroscopy (EIS) and membrane potential measurements in a free-standing membrane configuration. The charge transport processes showed a strong dependence on PANI deposition site in the base membrane along with PANI intercalation content. The transport processes in the membranes were modeled using equivalent circuit modeling technique. The composite membranes that had PANI layer at the surface showed highly resistive and diffusionally controlled charge transport. In contrast, in-pore PANI deposited membranes showed several orders of magnitude lower resistance and higher capacitance, both, were attributed to the redox transitions of PANI during the charge transport process. Membrane potential studies showed an anion-selective transport coupled with the proton conduction through the composite membranes. This study indicates the possible development of an electroactive porous membrane where the selective transport can be achieved through the electrochemical and electrostatic interactions of permeated species with in-pore deposited PANI layer.

High-resolution 13C nuclear magnetic resonance evidence of phase transition of Rb,Cs-intercalated single-walled nanotubes

We present 13 C high-resolution magic-angle-turning (MAT) and magic angle spinning nuclear magnetic resonance data of Cs and Rb intercalated single walled carbon nanotubes. We find two distinct phases at different intercalation levels. A simple charge transfer is applicable at low intercalation level. The new phase at high intercalation level is accompanied by a hybridization of alkali (s) orbitals with the carbon (sp2) orbitals of the single walled nanotubes, which indicate bundle surface sites is the most probable alkali site.

Electrochemical and spectroscopic characterization of lithium titanate spinel Li 4Ti 5O 12

Herein we describe electrochemical and spectroscopic properties of lithium titanate spinel as well as an easy method based on colorimetry to determine the lithium content of electrodes containing lithium titanate spinel as active material. Raman microspectrometry measurements have been performed to follow lithium insertion into and extraction from the active material, respectively. The Raman signals display a pronounced fading of intensity already at low levels of lithium intercalation and disappear at a SOC higher than ∼10%. However, the colorimetric method can be used up to a SOC of 50%.

Electronic properties of Cs-intercalated single-walled carbon nanotubes derived from nuclear magnetic resonance

We report on the electronic properties of Cs-intercalated single-walled carbon nanotubes (SWNTs). A detailed analysis of the 13C and 133Cs nuclear magnetic resonance (NMR) spectra reveals an increased metallization of the pristine SWNTs under Cs intercalation. The ‘metallization’ of CsxC materials where x=0–0.144 is evidenced from the increased local electronic density of states (DOS) n(EF) at the Fermi level of the SWNTs as determined from spin–lattice relaxation measurements. In particular, there are two distinct electronic phases called α and β and the transition between these occurs around x=0.05. The electronic DOS at the Fermi level increases monotonically at low intercalation levels x<0.05 (α-phase), whereas it reaches a plateau in the range 0.05⩽x⩽0.143 at high intercalation levels (β-phase). The new β-phase is accompanied by a hybridization of Cs(6s) orbitals with C(sp2) orbitals of the SWNTs. In both phases, two types of metallic nanotubes are found with a low and a high local n(EF), corresponding to different local electronic band structures of the SWNTs.

The Use of Apparent Yield Stress to Characterize Exfoliation in Polymer Nanocomposites

Abstract Nanocomposites based on melt blending of an organoclay and a thermoplastic matrix have end-use properties directly controlled by the state of dispersion of the clay and the resulting nanostructure. It is thus very important to be able to correctly quantify the levels of intercalation and exfoliation of these systems. For the exfoliation, rheological measurements in small amplitude oscillatory shear are very powerful because they put clearly in evidence the interactions between nanofillers. We show in this paper how it is possible to interpret the experimental results, we indicate the advantages and drawbacks of current methods used in the literature and we strongly suggest to use the melt yield stress to characterize exfoliation level.

Extrusion of linear polypropylene–clay nanocomposite foams

AbstractThis work presents new results on using organoclay with an appropriate polymeric compatibilizer as rheology‐modifying additives for extrusion foaming of a linear polypropylene (PP), which by itself does not display strain hardening in extensional flow of the melt. The uniaxial melt‐extensional viscosity behavior of several nanocomposites prepared with varying ratio of bound maleic anhydride to clay as well as varying compatibilizer molecular weight was investigated. A chemical‐blowing agent was used at a fixed concentration for foaming these nanocomposites in a single‐screw extruder. Among nanocomposites with similar levels of clay dispersion or intercalation, the ones that displayed significant strain hardening in the melt state along with slower crystallization led to extruded PP nanocomposite foams with smaller cell sizes and greater cell density by reducing cell coalescence. This was achieved with as little as 3 wt% organoclay and a high‐molecular weight PP‐g‐MA compatibilizer in linear PP. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Effects of unfolded and intercalated halloysites on mechanical properties of halloysite–epoxy nanocomposites

Phenylphosphonic acid (PPA) was used to unfold a unique tubular clay mineral, halloysite. By varying the durations of PPA treatment, halloysites with different levels of enfoldment and intercalation were obtained. Halloysites, particularly with the unfolded and intercalated halloysites, were effective additives in increasing the fracture toughness of the cured epoxies without sacrificing their basic properties. Fracture toughness of composites was increased with increasing intercalation levels of halloysite, with the improvement being 78.3% in KIC for the composite containing 10wt.% of the fully PPA-intercalated and unfolded halloysite. There was a substantial increase in the contact area between halloysite and epoxy, and as a result the morphology changed from nanotubes to nano-platelets in the composites with the treated halloysites. The treated halloysites achieved a better dispersion in epoxy and promoted the formation of a large number of micro-cracks and plastic deformations in the interfaces, resulting in an improvement in fracture toughness.

Electronic structure of Eu–C70 fullerides

The electronic structure of Eu-intercalatedC70 has been studied by a synchrotron radiation photoemission spectroscopytechnique. At low intercalation levels (below the stoichiometry ofEu3C70), the photoemission data clearly exhibit charge transfer from Eu 6sstates to the lowest-unoccupied-molecular-orbital (LUMO) and theLUMO + 1 ofC70. The amount of charge transfer reaches its maximum far before intercalationsaturation. Detailed analysis reveals that most of the 5d6s electrons ofEu occupy the so-called interstitial states in the saturation phase (Eu9C70). The interstitial states are induced by a Eu sub-lattice formedat heavy intercalation levels, and comprise substantial 6s-π hybridizedstates. The π states participating in the hybridization are mainly theHOMO − n (n = 6–10) orbitals. The PES data also reveal the semiconducting property for bothEu3C70 andEu9C70. The6s–(HOMO − n) hybridization and the semiconducting property should playimportant roles in understanding the ferromagnetic mechanism forEu9C70.

Molecular Dynamics of Natural Rubber/Layered Silicate Nanocomposites As Studied by Dielectric Relaxation Spectroscopy

The segmental chain dynamics in nonvulcanized and vulcanized natural rubber/layered silicate nanocomposites has been studied by dielectric relaxation spectroscopy. Special consideration has been devoted to the effect of clay type and loading on the time scale of the relaxation processes. Results reveal that the type and concentration of clay do not have an effect on the segmental mode of the NR matrix, while the vulcanization reaction slows down the segmental dynamics. A new mode, slower than the segmental dynamics but faster than the normal mode associated with the chain dynamics, has been observed for both vulcanized and nonvulcanized nanocomposites with fillers having high levels of intercalation. We attribute the new mode to a restricted segmental dynamics of natural rubber chains located at the clay/rubber interfacial regions.

Intercalation of stable organic radicals into layered inorganic host matrices: Preparation and structural characterization of Cd 1−xPS 3( metaMPYNN) 2x

The radical cation 2-(3- N-methylpyridinium)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3- N-oxide (abbreviated as m-MPYNN) is successfully intercalated into the layered host structure CdPS 3. The reaction proceeds via an ion exchange reaction from methanol solutions containing the radical iodide salt, leading to materials described by the compositional formula Cd 1− x PS 3( metaMPYNN) 2 x . Detailed characterization of the intercalates by chemical analysis, X-ray powder diffraction, EPR, and NMR spectroscopy indicate that the maximum uptake corresponds to x=0.20; attempts to produce higher intercalated materials result in the formation of a side product with inferred composition CdI 4( metaMPYNN) 2. Magnetic susceptibility measurements indicate Curie-like behavior for x=0.13, while at higher intercalation levels antiferromagnetic coupling is observed. The magnetic properties may be linked to the orientation of the radical ions relative to the host layers, which is also found to depend on x. While for the low-intercalated regime ( x=0.13) both a transversal intercalation with the N–O director pointing towards the layers, and a longitudinal orientation, with the long axis of the molecule pointing towards the layers are found, at larger x-values only the longitudinal orientation is present. 1H NMR chemical shifts indicate that the orientation greatly influences the molecular spin density distributions. Modern single and double resonance solid state NMR techniques have been introduced successfully to study the structural modifications of the host lattice and the details of the intermolecular guest/host interactions. Specifically the internuclear distance correlations extracted from selectively measured 1H– 31P magnetic dipole–dipole couplings via 31P/ 1H rotational echo double resonance (REDOR) experiments allow important conclusions regarding the orientation of the guest species relative to the inorganic layers.

Electrochromic Contrast Enhancement of Nanostructured Poly(3,4-ethylenedioxythiophene)-Polystyrene Sulfonate Films by Composition/Morphology Control

Poly(3,4-ethylenedioxythiophene) (PEDOT) films have been electropolymerized from an aqueous micellar polyethylene glycol (PEG) based solution containing sodium poly(styrenesulfonate) (NaPSS) and lithium trifluoromethanesulfonate. On varying the NaPSS content in the electrodeposition bath, two strikingly different nanostructured morphologies were obtained for ensuing PEDOT:PSS films and these have been correlated to the electrochemical and optical performance of the films. The films grown from the formulation with EDOT:NaPSS in a 1:3 weight ratio comprise of a nanoparticulate structure with a to date scarcely reported hexagonal structure. The film surface is also characterized by some unusual floral shapes encompassing elongated grains. TEM studies reveal that in the 1:3 film two dimensional (planar) PEDOT chains are stacked on top of each other with a vertical separation of 4.63 A. On the other hand the film generated from a 1:1 solution shows a texture wherein a random segregation of PSS particles is seen and this adversely affects the electrochromic response of the film. The larger charge storage capacity (4.9 mC cm(-2)), better charge reversibility during coloration and bleaching, good electrochemical cycling stability up to 2500 cycles, higher electronic conductivity and a superior coloration efficiency of 233 cm2 C(-1) at a photopic wavelength of 550 nm under ion intercalation levels of 0.058 to 1.2 mC cm(-2) shown by 1:3 film as compared to the performance of the 1:1 film are ramifications of fast ion movement promoted by the novel microstructure and the hexagonal modification which has rarely been achieved in PEDOT:PSS films.

Hybrid inorganic/organic composites of Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate prepared by co-precipitation

Inorganic/organic composite materials composed of Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with citrate (C 6H 5O 7 3−), malate (C 4H 4O 5 2−), or tartrate (C 4H 4O 6 2−) anions were prepared by a co-precipitation technique and characterized by X-ray diffraction and compositional analyses. The molecular orientation of the organic component in the interlayer space was determined. At low intercalation levels, citrate ion was inclined at an angle of 26° relative to the brucite-like layers of Mg–Al LDH. At higher solution concentrations, both the Mg(C 6H 5O 7) − complex and free C 6H 5O 7 3− were isotropically oriented in the interlayer space. For both malate·Mg–Al LDH and tartrate·Mg–Al LDH, the organic anions were inclined at 26° relative to the Mg–Al LDH layers regardless of anion concentration.

Valence state of Eu ions in C 60 fullerides

We have prepared Eu-intercalated C 60 films in ultra-high vacuum, with special attention to avoid oxygen contamination. X-ray photoelectron spectra were measured in situ. Eu 4f photoemission reveals that the valence state of Eu ions is divalent for all intercalation levels. C 1s photoemission exhibits evidence of both ionic and covalent contributions to the Eu–C 60 bonding. The results eliminate the controversy about the valence state of Eu ions in the literature, and can help to understand the ferromagnetism (FM) and the giant magnetoresistance (GMR) of Eu 6C 60.

Preparation and characterization of Mg–Al layered double hydroxides intercalated with benzenesulfonate and benzenedisulfonate

Mg–Al layered double hydroxides (Mg–Al LDHs) intercalated with benzenesulfonate (BS –) and benzenedisulfonate (BDS 2–) ions were prepared by coprecipitation and characterized by X-ray diffraction, FT-IR spectroscopy, and chemical analyses. The intercalated BS – and BDS 2– maintained their intrinsic molecular structures within the Mg–Al LDH interlayers. At low intercalation levels, the benzene ring of BS – in BS · Mg–Al LDH was inclined at 30° relative to the plane of the brucite-like layers of Mg–Al LDH. With increasing BS – content, the benzene ring adopted an additional configuration perpendicular to the Mg–Al LDH layers. In BDS-intercalated Mg–Al LDH, the benzene ring of BDS 2– was tilted at 26° relative to the plane of the Mg–Al LDH layers. Intercalation levels of BDS 2– were smaller than those of BS – despite the greater charge density of BDS 2–, which was likely attributable to a greater degree of electrostatic repulsion between intercalated anions.

Poly(ethylene terephthalate) nanocomposite fibers with new organomica via in situ intercalation

AbstractPoly(ethylene terephthalate) (PET) nanocomposites with a newly synthesized organomica (C16BIMD‐Mica) were obtained by using the in situ interlayer polycondensation of ethylene glycol with dimethylterephthalic acid. The PET hybrids were melt‐spun to produce monofilaments with various organoclay contents and draw ratios. The thermomechanical properties and morphologies of the PET hybrid fibers were determined using differential scanning calorimetry, thermogravimetric analysis, wide angle X‐ray diffraction, electron microscopy (SEM and TEM), and a universal tensile machine. The XRD analyses and TEM micrographs showed that the levels of exfoliation and intercalation could be controlled by varying the clay content. The thermomechanical properties of the PET hybrid fibers were found to be better than those of pure PET fibers. POLYM. ENG. SCI., 47:1820–1826, 2007. © 2007 Society of Plastics Engineers

Electronic structure of Li-intercalated oligopyridines: A comparative study by photoelectron spectroscopy

The role of nitrogen in the charge transfer and storage capacity of lithium-intercalated heterocyclic oligophenylenes was investigated using photoelectron spectroscopy. The development of new occupied states at low binding energies in the valence band region, as well as core level chemical shifts at both carbon and nitrogen sites, demonstrates partial charge transfer from lithium atoms to the organic component during formation of the intercalated compound. In small compounds, i.e., biphenyl and bipyridine derivatives, the position of the nitrogen heteroatom significantly affects the spacing between gap states in the Li-intercalated film; yet it has minimal effects on the charge storage capacity. In larger, branched systems, the presence of nitrogen in the aromatic system significantly enhances the charge storage capacity while the Li-N bond strength at high intercalation levels is significantly weakened relative to the nitrogen-free derivative. These observations have strong implications towards improved deintercalation processes in organic electrodes in lithium-ion batteries.

Structure and Properties of Nanocomposites with a Poly(ethylene terephthalate) Matrix

AbstractPolymer nanocomposites based on PET and with an intercalated and fairly dispersed nanostructure have been obtained in the melt state. The intercalation and dispersion levels, as well as the mechanical properties, were studied by varying the chemical nature and amount of the organic modification of the clay, as well as the clay content. The intercalation level of PET into the organoclay galleries was measured by following the increase in the interlayer distance upon mixing. The surfactant content did not influence the intercalation level but an interaction between the polymeric matrix and the surfactant, through a common polar character, led to improved intercalation. The modulus increases observed, and consequently the overall dispersion, almost did not depend on either the amount or the chemical nature of the organic modification of the clay used, suggesting that the parameters leading to a high degree of intercalation differ from those which lead to a high modulus of elasticity and therefore to a high dispersion level. The obtained increases in the modulus of elasticity that reflect the dispersion level were large, attaining a 41% increase with respect to that of the matrix after a 6 wt.‐% clay addition.magnified image

Lithium Intercalation into Nanocrystalline Brookite TiO[sub 2

Lithium intercalation in phase-pure nanocrystalline brookite TiO 2 is demonstrated for the first time. Galvanostatic studies show that 0.9 Li per formula unit can be intercalated into this phase in initial discharge. Ex situ X-ray diffraction studies on the electrodes at different levels of lithium intercalation show that the structure is stable toward lithium intercalation and deintercation. In the initial charge, an irreversible capacity loss is observed. However, on further cycling, the phase shows excellent cycling behavior. A reversible capacity of 170 mAhg -1 is observed even after 40 cycles.

Rheology of isothermally crystallized poly(butylene terephthalate) nanocomposites with clay loadings under the percolation threshold

AbstractThis article describes the structural evolution of clay in poly(butylene terephthalate) nanocomposites (PCNs) with clay loadings lower than the percolation threshold during the isothermal crystallization process. The study of the structure and rheological properties has revealed that the intercalation and detachment levels of clay are enhanced in samples crystallized at a high temperature (210 °C), in contrast to those of the original PCN, and this results in the formation of a rheological percolation network. However, for PCNs crystallized at a low temperature (190 °C), the further structural evolution of the tactoids is very small. All the experimental results indicate that the morphologies of clay can further evolve during the crystallization process, but the evolution level is strongly dependent on the crystallization temperature. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 229–238, 2007

Charge distribution of potassium intercalated Dy3N@C80 observed with core‐level and valence‐band photoemission

AbstractA photoemission study of potassium intercalated trimetal‐nitride fullerene Dy3N@C80 is reported. A continuous electron doping to the carbon cage with increasing potassium intercalation levels is observed as shape changes in the carbon‐sensitive ultra‐violet photoemission spectrum. X‐ray photoemission shows that the valence electronic state of the trivalent Dy ions is not affected by the additional charge in the fullerene cage. (© 2006 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)