Na+ Selective Fluorescent Tools Based on Fluorescence Intensity Enhancements,Lifetime Changes,and on a Ratiometric Response

Over the years, we developed highly selective fluorescent probes for K⁺ in water, which show K⁺-induced fluorescence intensity enhancements, lifetime changes, or a ratiometric behavior at two emission wavelengths (cf. Scheme 1, K1 – K4 ). In this paper, we introduce selective fluorescent probes for Na⁺ in water, which also show Na⁺ induced signal changes, which are analyzed by diverse fluorescence techniques. Initially, we synthesized the fluorescent probes 2 , 4 , 5 , 6 and 10 for a fluorescence analysis by intensity enhancements at one wavelength by varying the Na⁺ responsive ionophore unit and the fluorophore moiety to adjust different K_d values for an intra- or extracellular Na⁺ analysis. Thus, we found that 2 , 4 and 5 are Na⁺ selective fluorescent tools, which are able to measure physiologically important Na⁺ levels at wavelengths higher than 500 nm. Secondly, we developed the fluorescent probes 7 and 8 to analyze precise Na⁺ levels by fluorescence lifetime changes. Herein, only 8 (K_d=106 mm ) is a capable fluorescent tool to measure Na⁺ levels in blood samples by lifetime changes. Finally, the fluorescent probe 9 was designed to show a Na⁺ induced ratiometric fluorescence behavior at two emission wavelengths. As desired, 9 (K_d=78 mm ) showed a ratiometric fluorescence response towards Na⁺ ions and is a suitable tool to measure physiologically relevant Na⁺ levels by the intensity change of two emission wavelengths at 404 nm and 492 nm.     

Preparation of Poly(ε‐caprolactone)/Clay Nanocomposites by Microwave‐Assisted In Situ Ring‐Opening Polymerization

PCL/clay nanocomposites were prepared by microwave‐assisted in situ ROP of ε‐caprolactone in the presence of either unmodified clay (Cloisite® Na⁺) or clay modified by quaternary ammonium cations containing hydroxyl groups (Cloisite 30B). This PCL showed significantly improved monomer conversion and molecular weight compared with that produced by conventional heating. An intercalated structure was observed for the PCL/Cloisite Na⁺ nanocomposites, while a predominantly exfoliated structure was observed for the PCL/Cloisite 30B nanocomposites. Microwave irradiation proved to be an effective and efficient method for the preparation of PCL/clay nanocomposites.

     

Chiral poly(amide-imide)/organoclay nanocomposites derived from pyromellitoyl-bis-l-isoleucine and benzimidazole containing diamine: synthesis, nanostructure, and properties

In this study, a series of polymer–clay nanocomposite materials, consisting of organosoluble poly(amide-imide) (PAI) matrix and dispersed nanolayers of inorganic montmorillonite clay, were successfully prepared by solution dispersion technique. At first, the reactive organoclay was prepared by using protonated l-isoleucine amino acid as a swelling agent for silicate layers of Cloisite Na⁺. Then, organosoluble PAI containing isoleucine amino acid was synthesized through step-growth polymerization reaction of N,N′-(pyromellitoyl)-bis-isoleucine diacid and 2-(3,5-diaminophenyl)-benzimidazole under green condition using molten tetrabutylammonium bromide. This polymer was end-capped with amine end groups near the completion of the reaction to interact chemically with acidic group of organoclay. Finally, PAI/organoclay nanocomposite films containing 2%, 5%, 10%, and 15% of organoclay were prepared via solution intercalation method through blending of organoclay with the PAI solution. Dispersion of the modified clay in the PAI matrix resulted in a nanostructured material containing intercalated polymer between the silicate layers. Structures of exfoliation were confirmed by X-ray diffraction, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. Thermogravimetric analysis data indicated that the addition of organoclay into the PAI matrix increased the thermal decomposition temperatures of the obtained nanocomposites compared to the pure PAI.     

Flammability of carbon nanofiber–clay nanopaper based polymer composites

In this study, a hybrid nanopaper consisting of carbon nanofiber (CNF), and pristine montmorillonite clay (MMT, Cloisite Na⁺) was fabricated through a paper‐making process. The hybrid nanopaper was coated onto the surface of glass fiber (GF) reinforced polymer matrix composites through resin transfer molding process. The characterization results using scanning electron microscopy (SEM) and energy dispersion analysis of X‐ray (EDAX) show that the nanopaper had a porous structure and the polymer resin completely penetrated the hybrid nanopaper. The thermogravimetric analysis (TGA) test results revealed that the addition of MMT clay nanoparticles significantly enhanced the thermal stability of the nanopaper. The flammability of composite samples was evaluated by cone calorimeter test under a radiant heat flux of 50 kW/m². The peak heat release rate (PHRR) was dramatically reduced for the composites coated with the CNF–MMT nanopaper. For comparison, the composites coated with the CNF–organic MMT clay (OMT, Cloisite 20A) nanopaper were also evaluated with cone calorimeter test. The test results showed that the MMT clay was more effective than the OMT in the reduction of the PHRR. The combustion behavior of these samples was also examined by microscale combustion calorimetry (MCC) test. The PHRR obtained from the MCC test decreased with the MMT content in the nanopaper, which was in good agreement with cone calorimeter test results. Copyright © 2010 John Wiley & Sons, Ltd.     

Vibrational energy-harvesting performance of bio-sourced flexible polyamide 11/layered silicate nanocomposite films

The energy-harvesting efficiency of melt processed polyamide 11 (PA11) films and its nanocomposites have been investigated as a function of filler type and content. In the present work, nanoclays have been used as structural modifiers in a PA11 matrix. The nanocomposites were prepared using layered clays, Cloisite 20A, 10A, and Na⁺, by extrusion process through varying the filler content, 1, 2, 4, and 5?wt.%. The crystalline structure of these nanocomposites has been studied by X-ray diffractometer. It has been demonstrated that layered silicates are not significant for the structural quality of the obtained nanocomposites. Regarding the interlayer peak of different clays, it has also been revealed that Cloisite 20A is partially exfoliated, whereas 10A and Na⁺ are totally exfoliated in the PA11 matrix. From mechanical and dynamic mechanical analyses, it was found that the addition of layered silicates results in an increase in mechanical properties. The piezoelectric strain coefficient d₃₃ and dielectric constant ε_R have been measured on polarized films at ambient temperature. Among all the prepared nanocomposites only Cloisite Na⁺-loaded PA11 nanocomposites showed the best piezoelectric constant. This observation showed that piezoelectric constant not only depends on the crystalline phases but also on the nature of the filler. Cloisite Na⁺ is more polar than other modified clays and high polarity leads to a better polarization response. A specific method for the quantification of energy vibration recovery has been developed for these nanocomposites. The capabilities of vibrational energy recovery were studied on PA11 loaded with Cloisite Na⁺.     

Rheological properties of mixed solutions of cellulose and layered aluminosilicates in N-methylmorpholine-N-oxide

The structure and rheological behavior of cellulose solutions in the high-polarity donor solvent N-methylmorpholine-N-oxide containing particles of layered aluminosilicates of various natures, namely, natural hydrophilic montmorillonite (Cloisite Na⁺) and hydrophobized montmorillonite (Cloisite 20A), are studied. The rheological properties of the mixed systems cellulose-N-methylmorpholine-N-oxide-Cloisite Na⁺ and cellulose-N-methylmorpholine-N-oxide-Cloisite 20A are similar, although their structures are different. This similarity may be explained by the fact that the highly developed structure of the cellulose matrix phase resulting from strong interactions between polar components of the system exerts the decisive effect on the character of flow of mixed solutions. Therefore, the filler assumes the minor role. The concentration dependences of solution viscosity turn out to be atypical when the content of moisture in Cloisite 20A is increased above the equilibrium value and when M₂Cloisite Na⁺ nanoparticles modified in a certain manner are introduced into cellulose solutions.     

Thermogravimetric analysis of organoclays intercalated with the surfactant octadecyltrimethylammonium bromide

Summary High resolution thermogravimetric analysis has been used to study the thermal decomposition of montmorillonite modified with octadecyltrimethylammonium bromide. Thermal decomposition occurs in 4 steps.The first step of mass loss is observed from ambient to 100°C temperature range and is attributed to dehydration of adsorbed water. The second step of mass loss occurs between 87.9 to 135.5°C temperature range and is also attributed to dehydration of water hydrating metal cations such as Na⁺. The third mass loss occurs between 179.0 and 384.5°C; it is assigned to the loss of surfactant. The fourth step is ascribed to the loss of OH units due to dehydroxylation of the montmorillonite and takes place between 556.0 and 636.3°C temperature range. These TG steps are related to the arrangement of the surfactant molecules intercalating the montmorillonite. Changes in the basal spacing of the clay with surfactant are followed by X-ray diffraction. Thermal analysis provides an indication of the stability of the organo-clay.     

Preparation, characterization and electrochemical corrosion studies on environmentally friendly waterborne polyurethane/Na-MMT clay nanocomposite coatings

In this study, we present the first practical evaluation for the corrosion protection effect of waterborne polyurethane (WPU)/Na⁺-montmorillonite (Na⁺-MMT) clay nanocomposite coating. Typically, a series of waterborne polyurethane (WPU)/Na⁺-montmorillonite (Na⁺-MMT) clay nanocomposite materials have been successfully prepared by effectively dispersing the inorganic nanolayers of commercially purified Na⁺-MMT clay in WPU matrix through direct aqueous solution dispersion technique. First of all, WPU was prepared by polymerizing PCL, DMPA and H₁₂MDI, followed by characterized by nuclear magnetic resonance (¹H NMR), Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). Subsequently, the as-prepared PU/Na⁺-MMT clay nanocomposite (Na⁺-PCN) materials were subsequently characterized by FTIR, X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM).PCN materials in the form of coating at low Na⁺-MMT clay loading up to 3 wt% coated on the cold-rolled steel (CRS) coupons were found to exhibit superior corrosion protection effect over those of neat WPU based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and impedance in 5 wt% aqueous NaCl electrolyte. Effects of the material composition on the gas permeability, thermal stability and optical clarity of neat WPU along with a series of Na⁺-PCN materials, in the form of coating and free-standing film, were also studies by gas permeability analyzer (GPA), thermogravimetric (TGA), differential scanning calorimetry (DSC) and ultraviolet UV-visible transmission spectroscopy, respectively. As control experiments, a series of PU/organo-MMT nanocomposite (denoted by organo-PCN) materials were also prepared for comparative studies.     

Effect of montmorillonite on gelation and swelling behavior of sulfonated polyacrylamide nanocomposite hydrogels in electrolyte solutions

Nanocomposite hydrogels were prepared by cross-linking of aqueous solutions of sulfonated polyacrylamide/sodium montmorillonite with chromium triacetate. The gelation process and effects of clay content and ionic strength on swelling behavior were investigated. X-ray diffraction patterns indicated that exfoliated type of microstructure was formed. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the nanocomposite (NC) gels decreased with increasing clay content up to 1000 ppm, but it increased by further increase of Na⁺-montmorillonite concentration. It was also found that with increasing the clay content, the viscous energy dissipation properties of the nanocomposite gels increased. The swelling ratio of nanocomposite gels in tap water decreased as the concentration of the clay increased. However, nanocomposite gels showed higher resistance against syneresis in electrolyte solutions as compared with unfilled gels. Therefore, they are potentially good candidates for enhanced oil recovery applications.     

Multifold Fluorescence Enhancement in Nanoscopic Fluorophore–Clay Hybrids in Transparent Aqueous Media

Valuable emissive properties of organic fluorophores have become indispensable analytical tools in biophotonics, but frequently suffer from low solubilities and radiationless deactivation in aqueous media, that is, in biological ambience as well. In this report, nanoscaled dye–clay hybrids based on laponite, Na_0.7{(Li_0.3Mg_5.5)[Si₈O₂₀(OH)₄]}, are taken advantage of to solubilize neutral dyes, which are natively not encountered in water. Previously reported efficiency and solubility bottlenecks of such hybrids can to a large extent be overcome by comparably simple chemical measures, as demonstrated here for two prominent examples, the fluorescent dyes Nile Red and Coumarin 153. On controlled co‐adsorption of small bifunctional quaternary ammonium ions (Me₃N⁺C₂H₅OH and Me₃N⁺C₂H₅NH₂) we observed an outright efficiency boost by an order of magnitude, and a 30‐fold brightness gain. Even at higher concentrations, transparency and stability of the hybrid dispersions are retained, rendering them useful for employment as optically functional nanoparticles in bioassays and beyond.     

Advanced environmentally friendly anticorrosive materials prepared from water-based polyacrylate/Na-MMT clay nanocomposite latexes

A series of novel advanced environmentally friendly anticorrosive materials have been successfully prepared by effectively dispersing nanolayers of Na⁺-montmorillonite (Na⁺-MMT) clay into water-based polyacrylate latex (i.e., vinyl acrylic terpolymers). First of all, a polyacrylate latex was synthesized through co-polymerizing organic monomers of MMA, BMA and styrene (St) using conventional emulsion polymerization technique with SDS, 1-pentanol and KPS as surfactant, co-surfactant and initiator, respectively. Subsequently, the commercial purified hydrophilic Na⁺-MMT was effectively dispersing into the polyacrylate latex through the direct solution dispersion technique.The as-prepared neat polyacrylate and the series of water-based polyacrylate/Na⁺-MMT clay nanocomposite (Na⁺-PCN) materials were subsequently characterized by FTIR spectroscopy, XRD, TEM and GPC. The water-based Na⁺-PCN materials loaded with low content of Na⁺-MMT when in the form of coating on the cold rolled steel (CRS) coupons was found to be remarkably superior in anticorrosion efficiency over those of neat polyacrylate based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current, and impedance spectroscopy in saline. Effect of material composition on the molecular barrier, optical clarity and thermal stability were also studied by molecular permeability analysis, ultraviolet-visible transmission spectra, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. Organo-PCN materials were also prepared as a control experiment for comparative studies.     

Effects of organic modifications of clay on the ultraviolet‐curing behavior and structure of a polyester‐acrylate/clay nanocomposite system

A pristine clay (Na⁺‐montmorillonite (MMT) and three different organoclays (20A‐MMT, vinylbenzyl dimethyldodecyl ammonium (VDA)‐MMT, and siloxane diamine ammonium (SDA)‐MMT) that originated from the pristine clay were used to prepare polyester‐acrylate (PEA)/clay nanocomposites by in situ ultraviolet (UV)‐curing. Except for the commercial organoclay (20A‐MMT), VDA‐MMT, and SDA‐MMT were prepared in this study by ion exchange method. The effects of organic modifications of the pristine clay on the UV‐curing behavior and structure of the nanocomposite system were investigated. The organic modifications of the clay affected considerably the UV‐curing behavior and structure of the nanocomposite system. Copyright © 2008 John Wiley & Sons, Ltd.     

Modification of Na+-montmorillonite with mono- and bis(polyfluoroalkyl) phthalates

Layered natural aluminosilicate, Na⁺-montmorillonite, was modified with mono- and bis(polyfluoroalkyl) phthalates. The polyfluorinated esters as Na⁺-montmorillonite modifiers exhibit high organophilizing and hydrophobizing activity, as demonstrated by thermal analysis and IR spectroscopy. A change in the interlayer spacing in the clay was determined by X-ray diffraction. The capability of the modifier for intercalation into the layered structure of the clay depends on the degree of telomerization of the perfluoroalkyl residue.     

Radiation-induced synthesis of vinyl copolymer based nanocomposites filled with reactive organic montmorillonite clay

Vinyl copolymer–clay nanocomposites were prepared by γ-irradiation-initiated radical polymerization using a mixture of styrene (St) and divinyl benzene (DVB) in the presence of reactive organic montmorillonite clay (OMMT) in methanol at room temperature. Reactive OMMT was synthesized by a cation exchange reaction of Na⁺-MMT and 1-[(4-ethylphenyl)methyl]-3-butyl-imidazolium chloride as a reactive organic modifier in an aqueous solution. The microstructures of the nanocomposites were confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal stability was examined by thermo gravimetric analysis (TGA). As a result, the reactive OMMT was a good additive material for preparing vinyl copolymer–clay nanocomposites.     

Preparation and characterization of poly(o-methoxyaniline)/Na-MMT clay nanocomposite via emulsion polymerization: Electrochemical studies of corrosion protection

A series of poly(o-methoxyaniline) (PMA)/Na⁺-montmorillonite (MMT) clay nanocomposite (Na⁺-PCN) materials have been successfully prepared by in situ emulsion polymerization in the presence of inorganic nanolayers of hydrophilic Na⁺-MMT clay with DBSA and APS as surfactant and initiator, respectively. The as-synthesized Na⁺-PCN materials were characterized by Fourier-transformation infrared (FTIR) spectroscopy, wide-angle powder X-ray diffraction (XRD) and transmission electron microscopy (TEM).Na⁺-PCN materials in the form of coatings with low loading of Na⁺-MMT clay (e.g., 5 wt.%, CLMA5) on cold rolled steel (CRS) were found much superior in corrosion protection over those of neat PMA based on a series of electrochemical measurements of corrosion potential, polarization resistance, corrosion current and impedance spectroscopy in 5 wt.% aqueous NaCl electrolyte. The molecular weight of PMA extracted from Na⁺-PCN materials and net PMA were determined by gel permeation chromatography (GPC) with NMP as eluant. Effects of material composition on the optical properties, electrical conductivity, thermal stability and surface morphology of neat PMA and/or a series of Na⁺-PCN materials, in the form of solution, powder-pressed pellet and fine powder, were also studied by ultraviolet-visible spectra, four-point probe technique, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively.     

Influence of compatibilizer degradation on formation and properties of PA6/organoclay nanocomposites

Nanocomposites based on polyamide 6 (PA6) and commercial layered silicates have been prepared by both in situ polymerization and melt compounding. The main aim of the present work has been centred on compatibilizer degradation, caused by the preparation conditions, in terms of nanocomposite end features. Two montmorillonite (MMT)-type, organically-modified clays (OMLS), namely Cloisite 30B^® and Nanofil 784^®, and a sodium MMT (Cloisite Na^®) have been studied. Thermal properties of the layered silicates have been evaluated by TGA, IR, WAXD and pyrolysis-gas-mass. In order to better assess the influence of high temperature processes on clay modifications, a thermal treatment which mimics the conditions used during the in situ polymerization (4 h at 250 °C) has been applied on layered silicates. The above treatment, besides the elimination of absorbed water from all the clays, turned out to prove noteworthy differences in compatibilizer modification for the two organoclays. Indeed, in the case of Closite 30B^® only a removal of organic molecules outside the silicate galleries and a likely reorganization of those present inside the galleries have been detected, while a relevant chemical modification of Nanofil 784^® compatibilizer has been conversely found.As far as nanocomposite characteristics are concerned, the latter have been found to depend on both the preparation method and clay type. In the case of in situ polymerization, also thermally-treated layered silicates, coded (T), have been used, in order to put more clearly in evidence the role of compatibilizer decomposition on nanocomposite formation and properties. Indeed, nanocomposite samples containing Closite 30B^®(T) have been found to be completely exfoliated, while the same thermal treatment seems to make worse the properties of those based on Nanofil 784^®(T). Furthermore, with respect to nanocomposites based on pristine clays, samples containing thermally-treated silicates turned out to be different in terms of both molecular mass and crystal structure of the polymer matrix. Namely, PA6 γ-form seems to be promoted for all nanocomposites prepared in such a way, probably because of water removal at high temperature, which makes -OH groups of the layered silicate more free to interact with polyamide chains, thus causing a restriction of their mobility.     

The effects of reactive organoclay on the thermal, mechanical, and microstructural properties of polymer/layered silicate nanocomposites based on chiral poly(amide-imide)s

Considering the importance of the nanocomposites, the present work focuses on some new hybrid materials prepared by introducing reactive organoclay (OC) into the chiral poly(amide-imide) (PAI) matrix. At first, Cloisite Na⁺ was modified with protonated l-isoleucine amino acid. Then, PAI containing phenylalanine was synthesized via solution polycondensation of chiral diacid chloride with 4,4′-diaminodiphenylsulfone and was characterized with Fourier transform infrared (FTIR) and ¹H NMR techniques. At last, PAI/OC nanocomposite films containing 2, 5, 10, and 15 % of OC were prepared via solution intercalation method. The effect of OC dispersion and the interaction between OC and polymer chains on the properties of nanocomposites were investigated using FTIR, X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, tensile testing of thin films, and thermogravimetry analysis techniques. The thermal stability of hybrids such as the decomposition temperature and mass residue at 800 °C was improved. Mechanical data indicated improvement in the tensile strength of the nanocomposites with OC loading up to 10 wt%. The transparency of the hybrid films was investigated by means of UV–Vis spectra.     

Synthesis of organic nanoparticles of naphthalene-thiourea-thiadiazole-linked molecule as highly selective fluorescent and colorimetric sensor for Ag(I)

A novel fluorescent and colorimetric sensor was synthesized by a reprecipitation to probe Ag⁺ ions in water on naphthalene-thiourea-thiadiazole (NTTA) molecular nanocrystals. The fluorescent organic nanoparticles (FONs) allowed a highly sensitive determination of free Ag⁺ ions in aqueous media. The possible mechanism was discussed.     

The Heavy-Atom Effect on the Photophysics of Aromatic Hydrocarbons in the Presence of Solid Clays

The exchange of the original cation present on a Laponite clay (usually Na⁺) for heavy atoms such as Rb⁺, Cs⁺, and Tl⁺ significantly alters the emission characteristics of some aromatic hydrocarbons (p-terphenyl, naphthalene, pyrene, and biphenyl). The increase of the atomic mass of the cation induces a decrease of the fluorescence emission simultaneous with an increase of the emission in the region of lower energies of the spectra, ascribed to the phosphorescence of those hydrocarbons. Time-resolved experiments for the pyrene–clay system showed a decrease of singlet lifetimes for the heavier atoms. Hydrocarbon aggregates were also detected from both the emission spectra and the time-resolved studies. The “excimer-like” emission showed longer lifetimes (10–25 ns) than the monomolecular hydrocarbons (1–3 ns), as already found for other similar systems. The amount of aggregates increased for the heavier cations due to the smaller surface available on the clay particles. Experiments increasing the amount of Tl⁺ in samples containing a constant concentration of naphthalene allowed evaluation of the distance between the heavy atoms and the probe on the clay surface. The Perrin model treatment was used and resulted in approximately R₀=9.2 Å.     

Synthesis and Rheology of Intercalated Polystyrene/Na+‐Montmorillonite Nanocomposites

Polystyrene (PS)/clay nanocomposites were synthesized by the emulsion polymerization of styrene in the presence of sodium ion‐exchanged montmorillonite (Na⁺‐MMT), demonstrating that the strongly hydrophobic PS was intercalated into the hydrophilic silicate layers. The nanocomposites were examined by means of X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis. The rheological properties of the PS/Na⁺‐MMT nanocomposites were also studied to exhibit more pronounced shear thinning behavior with increasing clay content.