Fluorohectorite Research Articles

Physicochemical characterisation of fluorohectorite: Water dynamics and nanocarrier properties

Abstract Clay minerals such as fluorohectorite (FHt) have come into prominence as drug carrier systems due to their layered structure and excellent cation exchange capabilities. Water present in the interlayers of FHt is believed to facilitate the uptake of bio-active molecules in these systems, yet details of this interaction are not well understood. To shed light into this question, using quasi-elastic neutron scattering and the jump diffusion model, we determined the diffusion coefficients and the residence time of water in this synthetic smectite clay. We demonstrate how different interlayer cations (Li + , Na + and Ni 2 + ) and different hydration levels influenced water mobility in FHt. By means of the elastic window method and analysis of the thermal decomposition of samples with the drug Ciprofloxacin intercalated at pH 2 in LiFHt, we confirmed that the intercalation process removed most of the interlayer water previously present in the clay. Based on the Kissinger procedure, we also showed that thermal decomposition of the intercalated drug was activated at lower temperature. These findings are discussed in relation to the drug’s shelf life and might aid in the selection of clay systems for use as nanocarrier.

Optical manipulation of a single clay nanosheet hybridized with a porphyrin derivative

The effect of hybridization of a clay fluorohectorite (FHT) nanosheet with a π-conjugated organic compound, α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphyrin p-toluene-sulfonate (TMPyP), on its optical manipulation is investigated. Although the hybridized FHT is optically trapped essentially in the same manner as that of neat FHT, the hybridization with TMPyP allows for manipulation of FHT with lower laser intensity or a shorter period, or both. This is ascribed to the larger refractive index and polarizability of TMPyP compared with neat FHT.

The pH influence on the intercalation of the bioactive agent ciprofloxacin in fluorohectorite

Biocompatible encapsulated drug delivery materials are highly desired as they provide for controlled release of bioactive agents, thereby improving the effectiveness of medical treatments. Some of the key properties of better materials for drug delivery include high adsorptive capacity, which can be realized by smectites, a family of clay minerals. Here the influence of pH on encapsulation of the bioactive molecule ciprofloxacin (CIPRO), an antibiotic, by fluorohectorite (FHt), a synthetic smectite, was investigated. Aspects of the clay structure itself were also investigated. By means of X-ray powder diffraction (XRD), thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TGA/FTIR) and inelastic neutron scattering (INS), it is demonstrated that the capture of ciprofloxacin is more efficient at acidic pH. Geometric considerations based on the XRD results and mass calculations based on the TGA results provided evidence that at acidic pH, the CIPRO-FHt complex contained one CIPRO molecule per unit cell, while at neutral pH the CIPRO content was about half, despite having similar interlayer volume available. Finally it is shown that adsorption of CIPRO by FHt facilitated removal of residual water from the interlayer, providing additional evidence that intercalation is the main adsorptive mechanism at acidic pH. These results lead to a deeper understanding concerning the capture of amphoteric drug molecules by smectites, as well as concerning their molecular interactions, which may lead to more feasible application of clay minerals as a carrier for drug molecules.

Photoinduced Electron Transfer between Ruthenium-bipyridyl Complex and Methylviologen in Suspensions of Smectite Clays

We examined photoinduced electron transfer (PET) in multicomponent aqueous suspensions composed of tris(2,2′-bipyridine)ruthenium(II) (Ru(bpy)32+, photocatalyst), methylviologen (1,1′-dimethyl-4,4′-bipyridinium dication, MV2+, electron acceptor), and ethylenediamine tetraacetate (EDTA, sacrificial electron donor) together with particles of smectite-type clays although previous studies indicated inhibition of the electron transfer from Ru(bpy)32+ to MV2+ in the presence of clay particles. Clays with different lateral particle sizes were compared: hectorite (Hect) and saponite (Sapo) with small particle sizes (∼30 nm) and fluorohectorite (FH) and montmorillonite (Mont) with large particle sizes (>0.1 μm). Clay particles were flocculated and were settled in many cases after the addition of Ru(bpy)32+, MV2+, and EDTA species, and the Ru(bpy)32+ and MV2+ cations were almost all adsorbed on the clay particles. When Hect and Sapo were used, reduction of MV2+ was observed on the aggregated clay particles upon visible light irradiation indicating the occurrence of PET from Ru(bpy)32+ to MV2+. However, the reaction was not observed for the samples where the clay particles were not settled. When FH and Mont were used, PET was not observed irrespective of the flocculation of clay particles. These results demonstrated that PET from Ru(bpy)32+ to MV2+ in the presence of clay particles is possible when the clay particles with small sizes are appropriately aggregated to allow interparticle electron hopping.

Experimental comparison of manufacturing techniques of toughened and nanoreinforced polyamides

Composites consisting of polyamide-6 (PA-6), nitrile rubber (NBR), and sodium fluorohectorite (FH) or alumina silicate (Sungloss; SG) were produced by different techniques with latex precompounding. Their tensile and thermomechanical properties were determined by using tensile tests and a dynamic-mechanical analysis, performed at various temperatures. The PA-6/NBR composite systems produced by the direct melt compounding outperformed those obtained by using the masterbatch technique with respect to the strength and ductility, but the latter ones had a higher storage modulus.

Structure, mechanical, and fracture properties of nanoreinforced and HNBR-toughened polyamide-6

Hydrogenated nitrile rubber (HNBR) and synthetic nanofillers, viz. water-swellable sodium fluoro- hectorite (FH) and water dispersible boehmite alumina (BA), were used to toughen and reinforce polyamide-6 (PA- 6). FH and BA were introduced in HNBR latex that was dried prior to melt mixing with PA-6. Binary blend (PA-6/ HNBR) and ternary nanocomposites (PA-6/HNBR/nanofil- ler) were produced and their structure-property relation- ships studied. HNBR was coarsely and microscale dispersed in PA-6. FH, slightly intercalated, was present in PA-6 and in the PA-6/HNBR interphase, whereas BA was mostly located in the HNBR droplets. HNBR improved the ductility of the PA-6/HNBR blend at cost of stiffness and strength. The fracture toughness and energy, determined on notched Charpy specimens at different temperatures (T ¼ � 30 � C, room temperature, and T ¼ 80 � C) were improved by blending with HNBR at 9 wt %. Additional incorporation of the nanofillers in 2.5 wt % enhanced the stiffness and strength of the PA-6/HNBR blend but reduced its ductility. The fracture toughness of the ternary nanocomposites was between those of PA-6 and PA-6/HNBR, whereas their frac- ture energy fairly agreed with that of the parent PA-6. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 897-902, 2012

Effect of nanofiller aspect ratio on the stress relaxation and creep response of toughened pom composites

Ternary composites composed of polyoxymethylene (POM), polyurethane (PU), and sodium fluorohectorite (FH) or sodium bentonite (BN) were produced by the melt compounding masterbatch (MB) technique. The related MB was produced by mixing the PU latex with water-swellable FH or BN. The dispersion of the nanofillers in the composites was studied by X-ray diffraction techniques. The crystallization of the POM-based systems was inspected by polarized optical microscopy (PLM). The stress relaxation and creep properties of the composites were determined in short-time stress relaxation and creep tests (creep at various temperatures), respectively. The POM/PU/FH composites produced by the MB technique outperformed the POM/PU blend and the POM/PU/BN system in respect to most of the stress relaxation and creep characteristics. This fact was attributed to the higher aspect ratio of FH compared with that of BN. The master curves (creep compliance vs. time) constructed by employing the time-temperature superposition principle showed that the Findley power law was fully applicable to the experimental results obtained.

Effect of the layer charge on the interaction of porphyrin dyes in layered silicates dispersions

Interaction between tetracationic porphyrin, 5,10,15,20-tetrakis( N-methylpyridinium-4-yl)porphyrin (TMPyP), and layered silicates in aqueous dispersions was studied using absorption, steady-state and time-resolved fluorescence spectroscopies. The charge density of silicates increases in order synthetic laponite (LAP)<Kunipia F montmorillonite (KF)<synthetic fluorohectorite (FHT). Interpretations of the spectra of layered silicate–porphyrin (LSP) systems considered models of dye adsorption on clay mineral colloid particles, analyzing phenomena occurring in similar systems such as structural changes of TMPyP and the formation of dye molecular assemblies. Structural changes of TMPyP, including flattening of the porphyrin molecule, do not fully explain all the spectral observations. One should mention variations of the Q-bands and fluorescence spectra in dependence on the layer charge. The molecular association of the TMPyP molecules is expected to occur to a certain extent in dependence on the layer charge of a clay mineral template. H-aggregates were not observed in any system. Only FHT colloids induced the formation of at least two components with significantly different spectral properties.

Structure and creep response of toughened and nanoreinforced polyamides produced via the latex route: Effect of nanofiller type

Ternary composites composed of polyamide-6 (PA-6), hydrogenated nitrile rubber (HNBR) and sodium fluorohectorite (FH) or boehmite alumina (BA) were produced by melt blending with latex precompounding. The latter served for the predispersion of the FH and BA nanoparticles. The related masterbatch (MB) was produced by mixing the HNBR latex with water dispersible BA or water swellable FH. The dispersion of the nanofillers in the composites was studied by scanning and transmission electron microscopy techniques (SEM and TEM, respectively) and discussed. The thermomechanical and creep properties of the composites were determined in short-time creep tests (performed at various temperatures) and dynamic mechanical thermal analysis (DMTA), respectively. The melt flow of the composites was characterized in a plate/plate rheometer. PA-6/HNBR/FH composites produced by the MB technique outperformed the PA-6/HNBR/BA systems in respect to most of the mechanical and viscoelastic characteristics. This was attributed to the preferred location of FH in the PA-6 matrix and to its higher aspect ratio compared to BA.

Structure-stress relaxation relationship in polystyrene/fluorohectorite micro-and nanocomposites

Sodium fluorohectorite (FH) was incorporated into polystyrene (PS) in amounts of 4.5 and 7 wt.% by melt mixing, with and without latex precompounding. The latex precompounding was used for the latex-mediated predispersion of FH particles. The related masterbatch was produced by mixing PS latex with the water-swellable FH, followed by drying. The dispersion of FH in PS was studied by transmission-, scanning electron-, and atomic force microscopy techniques (TEM, SEM, and AFM, respectively). The stress relaxation in the PS composites was determined in short-term isothermal tests. The latter were performed at various temperatures between 25 and 75°C. The direct melt mixing of FH with PS resulted in microcomposites, whereas the masterbatch technique gave rise to nanocomposites. The master curves (relaxation modulus vs. time), constructed by applying the time-temperature superposition principle (TTSP), showed that the Williams-Landel-Ferry (WLF) equation, the Maxwell model, and the Findley power law were fairly applicable to the experimental results obtained.

Polystyrene–fluorohectorite nanocomposites prepared by melt mixing with and without latex precompounding: Structure and mechanical properties

AbstractSodium fluorohectorite (FH) was dispersed in polystyrene (PS) by direct melt blending with and without a master batch composed of PS and FH and produced by latex compounding. FH was not intercalated by PS when it was prepared by direct melt compounding. In contrast, FH was well dispersed (mostly intercalated) in PS via the PS‐latex‐mediated predispersion of FH following the master‐batch route. The dispersion of FH was studied with transmission and scanning electron microscopy and X‐ray diffraction techniques and discussed. The nanocomposites produced by the master‐batch technique outperformed the directly melt‐compounded microcomposites with respect to stiffness, strength, and ductility according to dynamic mechanical analysis and static tensile tests. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Effect of the aspect ratio of silicate platelets on the mechanical and barrier properties of hydrogenated acrylonitrile butadiene rubber (HNBR)/layered silicate nanocomposites

The role of the aspect ratio of the layered silicate platelets on the mechanical and oxygen permeation properties of hydrogenated nitrile rubber (HNBR)/organophilic layered silicate nanocomposites was investigated. Montmorillonite (MMT) and fluorohectorite (FHT) bearing the same type of intercalant (i.e., octadecylamine; ODA), however, showing different aspect ratio was involved in this study. The dispersion of the layered silicates was assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. Increasing aspect ratio (MMT < FHT) resulted in higher stiffness under uniaxial tensile loading. The dispersion state (“secondary structure”) of the organophilic layered silicates reduced dramatically the oxygen permeability of the rubber matrix based on the labyrinth principle. The lowest oxygen permeability was measured for the HNBR/FHT–ODA films in which the layered silicates had the highest aspect ratio. By varying the FHT–ODA volume fraction in the latter compound the mechanical and permeation properties were measured and modelled. It was found that the modified Guth’s and Nielsen’s equations predicted accurately the mechanical and permeation responses, respectively.

Multidimensional 2H NMR study of dynamical heterogeneity in polymer nanocomposites

Nanoconfined polymer chains—as can be formed when polymers intercalate into layered inorganic materials—show remarkable bulk properties, many of which are connected to dynamical heterogeneity in the polymeric phase. Microscopically, it appears that slow dynamical modes are associated with the species in direct contact with the surface, with substantially more mobile species only a fraction of a nm away. In the more distant phase, larger angle and moderately fast dynamics (typically, ns– μ s ) grows in over a broad temperature range not well correlated to bulk phase transitions. In this work, we probe the slowest dynamical modes and apply one- and two-dimensional 2H exchange NMR experiments to study thin polymer layers intercalated between the flat inorganic faces of fluorohectorite (FH). One sample is created by intercalation of perdeuterated poly(ethylene oxide) into FH, and the second by intercalation of d 3 -poly(styrene) into a surface-modified FH. Large-amplitude reorientation of the PEO backbone is substantially hindered in the narrow two-dimensional layers, and reorientation is limited to small-amplitude steps at rates that are largely independent of temperature. Simulations of the two-dimensional exchange experiments suggest that dynamics in nanoconfined polymers is associated with small-angle rotational diffusion.

Electrospinning of poly(MMA- co-MAA) copolymers and their layered silicate nanocomposites for improved thermal properties

Copolymers consisting of methyl methacrylate (MMA) and methacrylic acid (MAA) and their layered silicate nanocomposites were electrospun to form fibers with diameters in the sub-micron range. The presence of MAA increased the T g and thermal stability of the copolymers through formation of anhydrides upon heating. Fibers of uniform diameters were obtained for the poly(MMA- co-MAA) copolymers and nanocomposites containing montmorillonite (MMT), while protrusions were observed on the electrospun fibers from nanocomposites containing fluorohectorite (FH). The electrospinnability of copolymer solutions and nanocomposite dispersions predicted based on both rheological analyses and conductivity measurements correlates well with the experimental electrospinning observations. Dispersion of clays within the nanocomposites improved the electrospinnability of the nanocomposite dispersions. MMT is predominantly exfoliated and well distributed within the fiber and oriented along the fiber axis. Char formation was observed when the MMT-containing fibers were heated above the decomposition temperature, indicating a potential for reduced flammability and increased self-extinguishing properties, whereas the FH-containing materials disintegrated into either film or powder form.

Molecular Orientation of Rhodamine Dyes on Surfaces of Layered Silicates

Films of the layered silicates fluorohectorite (FH) and saponite (Sap) with various rhodamine dyes were prepared. The dyes with acidic as well as large hydrophobic groups in their molecule were not adsorbed on the surface of FH, which was interpreted in terms of high charge density on the surface of this silicate. All adsorbed dyes formed similar forms, such as isolated cations and H-type molecular aggregates, which were characterized by different spectral properties. Polarized ultraviolet-visible (UV-vis) spectroscopy was used for the characterization of the molecular orientation of dye chromophores on the silicate surface. The isolated dye cations and species, which absorbed light at the low energy part of the spectra, were only slightly tilted with respect to the plane of the silicate surface. The cations forming H-aggregates and absorbing light at low wavelengths were oriented in a nearly perpendicular fashion. The nearly perpendicular orientation was observed as a strong increase of dichroic ratio with film tilting. The orientation of the cations in H-aggregates depends partially on the structure of the dye molecule, namely, on the type of amino group (primary, secondary, or tertiary) in the dye molecule. The type of amino groups probably plays a role in the suitable orientation of dye cations for effective electrostatic interaction between the cations and the negatively charged siloxane surface. X-ray powder diffraction could not distinguish dye phases of dye monomers and molecular aggregates.

The aggregation of thionine and methylene blue dye in smectite dispersion

Interaction of cationic dyes, thionine (Th) and methylene blue (MB), with smectites in the aqueous dispersions was investigated using visible spectroscopy. Smectite samples of various layer charge were used: low-charge laponite (Lap), middle-charge Kunipia F montmorillonite (Kun) and high-charge fluorohectorite (FH). Dyes cations formed monomers, dimers and larger-size aggregates of H-type (sandwich type) and in a few cases of J-type (head-to-tail association). Each form of the dye was identified using visible (VIS) spectroscopy. The effects of layer charge, the type of the dye and smectite, and the influence of dye/clay ratio on the formation of specific dye species were compared. Negligible influence of the dye loading was observed for most cases, being always much lower than the effect of the layer charge density. Dye/Lap reaction systems were dominated by isolated dye cations. H-dimers and larger-size molecular aggregates were formed on the surface of this clay only at the highest loading tested (0.50 mmol/g). On the other hand, the reaction systems with a middle-charge Kun montmorillonite contained roughly equal amounts of dye monomers and H-aggregates at low loadings and slightly more H-aggregates were formed at high loadings. The spectra of dye/FH reaction systems were always dominated by the bands assigned to H-aggregates. The surface of high-charge densities induced destabilization and decomposition of Th cations especially at high dye concentrations on clay surface. The effects of silicate structure and composition on the optical properties of adsorbed dyes were not identified.

Homostructured Mixed Inorganic−Organic Ion Clays: A New Approach to Epoxy Polymer−Exfoliated Clay Nanocomposites with a Reduced Organic Modifier Content

A new approach to the preparation of epoxy−clay nanocomposites is reported based on the intercalation and exfoliation of homostructured mixed inorganic/organic cation exchanged forms of a commercially available montmorillonite (PGW) and a synthetic fluorohectorite (FH) clay. In these mixed-ion homostructures both the organic onium ions and the inorganic exchange ions co-occupy the gallery surfaces of the clay, thereby dramatically reducing the amount of organic modifier needed to access the galleries for nanocomposite formation. The homostructures were prepared by ion exchanging the inorganic H+ and Li+ forms of the smectite clays with diprotonated primary α,ω-diamines of the type H2NCH(CH3)CH2[OCH2CH(CH3)]xNH2 (denoted Jeffamine D2000 with x = 33.1). Varying the ratio of inorganic cations to onium ions afforded homostructured mixed-ion intercalates with basal spacings ranging from ∼17 A (25% onium ion exchange) to ∼46 A (65% onium ion exchange), indicating the Jeffamine D2000 modifier adopted extended ch...

Combustion behaviour of EVA/fluorohectorite nanocomposites

Octadecylammonium (ODA) or aminododecanoic acid (ADA) exchanged fluorohectorite (FH) was dispersed in ethylene–vinyl acetate copolymer (EVA) in an internal mixer. A nanocomposite was obtained in the case of FH/ODA with exfoliation of the FH crystalline layers which were separately distributed in EVA as shown by X-ray diffraction (XRD). Whereas distribution of particles formed by multiple crystalline layers with overall size of the order of 1 micron resulted in the case of FH/ADA. In the horizontal combustion mode of the mass loss calorimeter, the nanocomposite shows acceleration of EVA deacetylation and delayed volatilisation of the resulting polyene. The overall heat release rate is much lower than in the case of EVA as measured by the gas combustion temperature. A partial protection of EVA from the flame is also found in the case of the immiscible composite although in this case the volatilisation of the polymer during combustion occurs at a larger rate than in EVA alone. Cumulation of the silicate on the surface of the burning specimen may create a protective barrier to heat and mass transfer which is however much more effective in the case of ablative reassembling of crystalline layers of the nanocomposite than in that of the particles of the immiscible composite. Dripping of burning particles in vertical combustion is suppressed only in the case of the nanocomposite which reduces the hazard of fire spread to surrounding flammable materials.

Spectroscopic Studies on the Interaction of Tetramethylpyridylporphyrins and Cationic Clays

In the present work, the interaction between5,10,15,20-tetrakis(1-methyl-4-pyridyl)-21H,23H-porphine (TMPyP) and its metallated form(CoTMPyP) with three cationic clays was investigatedby X-ray diffraction (XRD), UV-VIS and resonance Ramanspectroscopies. Sodium montmorillonites K10 and KSFand a synthetic fluorohectorite (FHT) containingdifferent macrocycle loadings, were prepared by an ionexchange reaction. In nonsaturated KSF and FHT, theCoTMPyP molecule assumes a flat orientation, relativeto the host layers, giving rise to at least twoabsorption bands in the Soret region (ca. 445 and 465 nm)assigned to adsorbed and intercalated CoTMPyP,respectively. For the delaminated K10 sample, a broadband centered around 456 nm, indicates a majorcontribution from the metalloporphyrin on the clayexternal surfaces. The electronic spectra of FHTsamples containing increasing amounts of CoTMPyPshow bands red shifted even when a small amount ofporphyrin is used, suggesting that the electroniclevels of the macrocycle are more affected by theinteraction with the clay than by the metalloporphyrindistortion inside the galleries. The resonance Ramanspectra obtained for all CoTMPyP samples presentedonly minor shifts in peak positions and band width,with the exception of the FHT saturated sample, wherethe bands are clearly broader when compared to otherloadings, suggesting that porphyrin aggregation isoccurring. In the case of TMPyP, the bands at ca. 430and 468 nm were assigned to nonprotonated andprotonated molecules, respectively. This assignment issupported by resonance Raman spectroscopy, which alsoshowed the ν2 mode (ca. 1550 cm-1) to bethe most sensitive peak to protonation.

Percolation and diffusion in two-dimensional microporous media: Pillared clays

We have investigated the adsorptive and diffusive properties of N2, H2O, and rare gas atoms (Ar and He) in the pillared layered silicate clay systems [Cr(en)3+3]x[Co(en)3+2−(en)]1−x−L, where L is vermiculite (V), fluorohectorite (FHT), or montmorillonite (M), and (en) is an ethylenediamine ligand. In these mixed ion intercalates the intercalated [Cr(en)3+3] cation, where all three en ligands are coordinated to chromium, represents a laterally small pillaring agent, whereas [Co(en)3+2−en] represents a laterally large, ligand-dissociated species. Such systems are excellent models for two-dimensional microporous media. Adsorption measurements were carried out for N2, H2O, and Ar and diffusion studies were performed using simulation methods for both Ar and He. We find that the adsorptive and diffusive properties depend sensitively on the size of the diffusing species and the concentrations x and (1−x) of the intercalants. For Ar adsorption in the FHT system we observe a percolative response when x reaches 0.79. Using simple geometrical models to describe these microporous media, along with computer simulation, we can understand the x=0.79 percolation threshold. In addition, simulation studies of the relative diffusion rates of He and Ar for x=0 and 1, and comparison of these rates with experimental measurements by Zhou and Solin, suggest that He diffusion near narrow constrictions may be strongly suppressed by quantum effects.