Ethylene vinyl acetate/nanoclay‐based pigment composites: Morphology,rheology, and mechanical,thermal, and colorimetric properties

In this study, a new type of nanopigment, obtained from a nanoclay (NC) and a dye, was synthesized in the laboratory, and these nanopigments were used to color an ethylene vinyl acetate (EVA) copolymer. Several of these nanoclay‐based pigments (NCPs) were obtained through variations in the cation exchange capacity (CEC) percentage of the NC exchanged with the dye and also including an ammonium salt. Composites of EVA and different amounts of the as‐synthesized nanopigments were prepared in a melt‐intercalation process. Then, the morphological, mechanical, thermal, rheological, and colorimetric properties of the samples were assessed. The EVA/NCP composites developed much better color properties than the samples containing only the dye, especially when both the dye and the ammonium salt were exchanged with NC. Their other properties were similar to those of more conventional EVA/NC composites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2987–2994, 2013     

Structure,electrical, dielectric,and optical investigation on polyvinyl alcohol/metal chloride nanocomposites

Different concentrations of metal chlorides/polyvinyl alcohol nanocomposites have been prepared by the typical solvent cast technique. The prepared samples were investigated by different techniques such as X‐ray diffraction, differential scanning calorimetry, and scanning electron microscope. DC and AC conductivities are examined at different temperatures and frequencies. An activation process was found in the DC conductivity versus temperature relation and the activation energy was calculated. The AC conductivity obeyed the ω^S power law. The behavior of S with temperature was studied. Various dielectric parameters such as dielectric constant (ε′), dielectric loss (ε″) and loss tangent (tan δ) have been determined in the temperature range 303–443 K at different frequencies. The dielectric parameters were found to decrease with increasing frequency. The study of dielectric relaxation as a function of temperature at constant frequency shows two relaxation mechanisms. The optical band gaps and band tails were estimated from the measured absorption spectra. The applied photon energy found to affect the observed optical band gaps. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

NIR-responsive Fe3O4@PPy nanocomposite for efficient potential use in photothermal therapy

In this work, superparamagnetic Fe₃O₄@PPy nanocomposite with core-shell structure having strong near-infrared (NIR) absorption is synthesized via a facile two-step modified procedure. The prepared nanocomposite samples are characterized by UV–vis, FTIR, SEM, TEM, VSM, and XRD. The effects of laser power density (1.5–2.5 W cm⁻²) and aqueous concentration (0.01–0.2 mg ml⁻¹) of the nanocomposite on the photothermal performance are investigated in the NIR region (808 nm). At 0.1 mg ml⁻¹ concentration, the temperature reaches up to 50.1°C, 64.1°C, and 78.4°C within 10 min, under 1.5 W cm⁻², 2.0 W cm⁻², and 2.5 W cm⁻² NIR laser power density values, respectively. Photothermal conservation efficiency is calculated as 43.9% and the nanocomposite exhibits excellent photothermal stability. In summary, the core-shell Fe₃O₄@PPy nanocomposite is a promising candidate for photothermal therapy and simultaneous magnetic field-guided treatments.     

Synthesis and characterization of s‐histidine‐derived poly (ionic liquid)/silica nanocomposites and their application in the enantioselective hydrolysis of a chiral ester

In this study, a new optically active monomer containing two chemically preformed imide rings was synthesized. The monomer was then used to synthesize optically active poly(amide imide)s (OAPAIs) and an optically active polyionic liquid (OAPIL), which were finally reacted with various amounts of silica nanoparticles in an in situ polymerization reaction to produce OAPAI/SiO₂ and OAPIL/SiO₂ hybrid materials containing sulfonic acid groups. The prepared monomers and the OAPAI and OAPIL nanocomposites were characterized by ¹H‐NMR spectroscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, X‐ray diffraction, scanning electron microscopy, X‐ray photoelectron spectroscopy, and differential scanning calorimetry. OAPIL/SiO₂ served as an excellent catalyst in water as a solvent for the hydrolysis of d ,l ‐phenylglycine methyl ester with the advantage of a markedly enhanced enantioselectivity and activity. Also, the enantioselectivity was strongly dependent on the SiO₂ content in the OAPIL/SiO₂ systems; a favorable SiO₂ content was 20% (w/w). The enantioselectivity was 95.2% (substrate conversion = 62.3%). © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39595.     

The optical properties of PVA/TiO2 composite nanofibers

The electrospun nanofibers emerge several advantages because of extremely high specific surface area and small pore size. This work studies the effect of PVA nanofibers diameter and nano‐sized TiO₂ on optical properties as reflectivity of light and color of a nanostructure assembly consisting polyvinyl alcohol and titanium dioxide (PVA/TiO₂) composite nanofibers prepared by electrospinning technique. The PVA/TiO₂ composite spinning solution was prepared through incorporation of TiO₂ nanoparticles as inorganic optical filler in polyvinyl alcohol (PVA) solution as an organic substrate using the ultrasonication method. The morphological and optical properties of collected composites nanofibers were highlighted using scanning electron microscopy (SEM) and reflective spectrophotometer (RS). The reflectance spectra indicated the less reflectance and lightness of composite with higher nanofiber diameter. Also, the reflectance and lightness of nanofibers decreased with increasing nano‐TiO₂ concentration. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Measurements of size distribution nanoparticles in ultraviolet‐curable methacrylate‐based boehmite nanocomposites

A deep study on the possibility to increase the quality of the dispersion of organically modified Boehmite nanoparticles into photo‐polymerizable methacrylic‐siloxane monomers, to be used as coatings, was conducted using unconventional indirect analyses. The nanocomposite were produced using two different procedures, starting from the conventional “solvent dispersion method.” The two procedures used differ for the technique used to obtain the dispersion of Boehmite, i.e., sonication or magnetic stirring and for the time used in each procedure. The efficiency of each method of preparation of nanostructured systems was analyzed, both in the liquid (uncured) and ultraviolet (UV) cured state. First, dynamic light scattering and rheological measurements were performed on the liquid suspensions, supplying experimental data used in proper theoretical models to estimate the dimensions and distribution of Boehmite particles. The suspensions obtained with the two different methods were, then, UV cured obtaining thin and thick films, on which scanning electron microscopy and transmittance measurements were performed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Preparation and characterization of new nanocomposite polymer films containing NiO nanofillers

Nanocomposite solid polymer films based on the poly(exo‐N‐phenyl‐7‐oxanorbornene‐5,6‐dicarboximide) (PPhONDI)/LiClO₄/NiO system have been designed, and the effect of inorganic NiO nanofiller in different amounts on the film properties has been examined. The exo‐PPhONDI/LiClO₄/NiO polymer system is the first solid nanocomposite polymer electrolyte film example based on a ring‐opening metathesis polymerization (ROMP) host polymer. The NiO nanoparticles were prepared by two‐step chemical syntheses, and the thermoplastic host polymer, exo‐PPhONDI, was synthesized via ROMP. Composite polymer films were prepared by the solution‐casting method. The amount of nanoparticles was varied from 1 to 15 wt % of NiO. The conductivity of the nanocomposite solid polymer systems was influenced by the NiO nanofiller concentration. The composite films based on exo‐PPhONDI ROMP polymer with the highest conductivity were achieved for the composition with 8 wt % of NiO nanofiller and 10 wt % of LiClO₄ dopant. The prepared films were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy (SEM). The SEM results showed that the filler was well distributed in the polymer matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45938.     

One‐pot synthesis,characterization, and field emission investigations of composites of polypyrrole with graphene oxide,reduced graphene oxide,and graphene nanoribbons

Pyrrole monomer was polymerized by a chemical oxidative route in the presence of graphene oxide (GO), reduced GO (rGO), and graphene nanoribbons (GNR) separately to prepare composites of polypyrrole (PPy) as PPy–GO, PPy–rGO, and PPy–GNR, respectively. The morphological, chemical, and structural characterization of the as‐synthesized products was carried out using scanning electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Field emission studies of the PPy–GO, PPy–rGO, and PPy–GNR emitters were performed at the base pressure of 1 × 10^?8 mbar in a planar “diode” configuration. The turn‐on field values, corresponding to an emission current density of 1 µA/cm², are observed to be 1.5, 2.2, and 0.9 V/µm for the PPy–GO, PPy–rGO, and PPy–GNR emitters, respectively. The maximum emission current density of 2.5 mA/cm² is drawn from PPy–GO at an applied electric field of 3.2 V/µm, 1.2 mA/cm² at 3.6 V/µm from the PPy–rGO, and 8 mA/cm² at 2.2 V/µm from the PPy–GNR emitters. All of the composites exhibit good emission stability over more than 2 h. The results indicate the potential for a facile route for synthesizing composites of conducting polymers and graphene‐based materials, with enhanced functionality. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45170.     

Optical sensor based on fluorescent PMMA/PFO electrospun nanofibers for monitoring volatile organic compounds

The development of polymeric materials with superior electrical and/or optical properties is highly demanded for designing optical gas sensors, where conjugated polymers play an important role due to their π‐electron conjugation. However, usually the low processability and high cost of these materials hinder technological applications. Here we report on a simple route to develop highly fluorescent electrospun nanofibers of poly(methyl methacrylate) (PMMA) containing low contents of polyfluorene (PFO). The PMMA_PFO nanofibers were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis, while the luminescence properties changes were evaluated by exposing the PMMA_PFO nanofibers to distinct volatile organic compounds (VOCs) including ethanol, toluene, tetrahydrofuran, acetone, dichloromethane, and chloroform. The changes in luminescence properties, specifically fluorescence quenching, of PMMA_PFO nanofibers were analyzed in terms of conformational changes from glassy‐phase to β‐phase of PFO when the nanofibers were exposed to the VOCs. The developed nanostructured platform showed a suitable response to detect chloroform, with linear responses in the concentration range from 10 to 300 ppm and from 350 to 500 ppm and limits of detection of 47.9 and 15.4 ppm, respectively. The results suggest the PMMA_PFO electrospun nanofibers are highly potential materials for optical gas sensor applications based on luminescence quenching. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46128.     

Transparency and water vapor barrier properties of polybenzoxazine‐silica nanocomposites provided with perhydropolysilazane

Poly[6,6′‐(1‐methylethylidene)bis(3,4‐dihydro‐3‐2H‐1,3‐hexylbenzoxazine)] (PB‐hda)‐silica nanocomposites were synthesized with perhydropolysilazane (PHPS) and PB‐hda by ring opening polymerization in one step. Both high transparency and good water vapor barrier property (WVP) are required to be improved in the field of packing and electronic materials, such as OLED, solar cell, and electronic paper. PB‐hda has shown high toughness and high thermal stability. However, it became dark brown and showed a reduction of WVP with increasing curing temperature, which make it difficult to be applied to packing and electronic materials. In this study, we aim to improve transparency and WVP by addition of PHPS into PB‐hda matrix. It was found that nanocomposites showed the improvement of WVP and transparency owing to Si? O? C linkages between PB‐hda and PHPS. In particular, a nanocomposite with 1 wt % of silica showed the most significant improvement in terms of transparency and the WVP. These properties were found to be influenced by the thickness of the combined polymer‐silica layers that formed around the silica particles; these layers were thickest in the 1 wt % sample. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44238.     

Preparation and characterization of acrylic acid/itaconic acid hydrogel coatings containing silver nanoparticles

Hydrogel silver nanocomposites have been used in applications with excellent antibacterial performance. Acrylic acid (AA)/itaconic acid (IA) hydrogels silver nanocomposites were prepared and applied as a coating on a textile substrate. Hydrogel matrices were synthesized first by the polymerization of an AA/IA aqueous (80/20 v/v) solution and mixed with 2‐2‐azobis(2‐methylpropionamide) diclorohydrate and N,N′‐methylene bisacrylamide until the hydrogel was formed. Silver nanoparticles were generated throughout the hydrogel networks with an in situ method via the incorporation of the silver ions and subsequent reduction with sodium borohydride. Cotton (C) and cotton/polyester (CP) textile fibers were then coated with these hydrogel silver nanocomposites. The influence of these nanocomposite hydrogels on the properties of the textile fiber were investigated by infrared spectroscopy (attenuated total reflectance), scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and antibacterial tests against Pseudomona aeruginosa and Staphylococcus aureus. The better conditions, in which no serious aggregation of the silver nanoparticles occurred, were determined. It was proven that the textiles coated with hydrogels containing nanosilver had an excellent antibacterial abilities. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2713–2721, 2013     

Replication of laser‐textured alumina surfaces by polydimethylsiloxane: Improvement of surface hydrophobicity

Alumina tiles are textured by a laser beam to obtain improved hydrophobic characteristics at the surfaces. Since the textured surfaces are optically opaque, the resulting surfaces are copied and replicated by polydimethylsiloxane (PDMS). Some of the texture features such as whiskers‐like structures with complex shapes could not be copied by PDMS and synthesized silica particles are deposited onto PDMS copied and replicated surfaces to create a lotus effect. Analytical tools are incorporated to characterize the PDMS copied and replicated surfaces as well as synthesized silica particles deposited surfaces. Dynamic water contact angle measurements are carried out to assess hydrophobic characteristics of the resulting surfaces. It is found that PDMS copied and replicated surfaces have almost identical surface texture morphology to that of laser treated surface. Introducing synthesized silica particles improved the lotus effect on the PDMS copied and replicated surfaces; in which case, the hysteresis of droplet contact angle remains significantly low. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44015.     

Preparation and characterization of octadecane/polyurea nanocapsule‐embedded poly(ethylene oxide) nanofibers

This article describes the preparation and characterization of latent heat storage poly(ethylene oxide) nanofibers (LHS‐PEO nanofibers) with octadecane/polyurea (PCM/PU) nanocapsules. PCM/PU nanocapsules were prepared by interfacial polycondensation from toluene 2,4‐diisocyanate and ethylene diamine in a resin‐fortified emulsion system. LHS‐PEO nanofibers were prepared using an electrospinning procedure with varying PCM/PU nanocapsules content, i.e., from 0 to 8 wt %. The PCM/PU nanocapsules were polydisperse with an average diameter of 200 nm. The melting and freezing temperatures were determined as 23.7 and 28.2°C, respectively, and the corresponding latent heats were determined as 123.4 and 124.1 kJ kg^?1, respectively. The encapsulation efficiency of the PCM/PU nanocapsules was 78.1%. The latent heat capacity of the LHS‐PEO nanofibers increased as the PCM/PU nanocapsules content increased. Defects, such as holes and disconnection of the nanofibers, were observed, particularly inside the LHS‐PEO nanofibers. For packaging applications, mats were fabricated from the nanocapsules‐embedded nanofibers with varying nanocapsule content and the mats’ surface temperatures were monitored with a thermal imaging camera. The results proved the feasibility of using the LHS‐PEO nanofibers for thermal energy storage and functional packaging materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42539.     

Fabrication of PFO‐DBT:OXCBA nanostructured composite via hard template

Poly[2,7‐(9,9‐dioctylfluorene)‐alt−4,7‐bis(thiophen‐2‐yl)benzo‐2,1,3‐thiadiazole] (PFO‐DBT) and o‐xylenyl‐C₆₀‐bisadduct (OXCBA) nanostructured composite has been fabricated via the hard porous alumina template‐directed method. Spin‐coating technique at the spin rate of 1000 rpm is used to assist the infiltration of polymer solution into porous template. PFO‐DBT nanotube is fabricated by replicating the porous alumina template before the formation of PFO‐DBT:OXCBA nanostructured composite. Formation of nanostructured composite is completed once the infiltration of OXCBA solution into PFO‐DBT nanotubes is achieved. Detailed results of morphological, structural, and optical properties of PFO‐DBT nanostructures (nanorods and nanotubes) of different solution concentrations are reported. By tuning the optical properties of PFO‐DBT nanostructures, the effect of solution concentration on the optical properties can be realized. The promising PFO‐DBT nanotubes are chosen for the further fabrication of OXCBA:PFO‐DBT nanostructured composite that acts as a core and shell, respectively. Although the nanostructured composite of PFO‐DBT:OXCBA yield low light absorption intensity, the absorption spans the whole visible region and produce low optical energy gap. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44228.     

Synchronization of thermal properties and constituents in Nanocomposite: Manufacturing,characterization, adjustable properties

This is critical to maintain better thermal properties, especially thermal conductivity as well as low particle content along with organized particle dispersion in polymer nanocomposites. Thus, this study is designed to develop a nanocomposite containing a constant reinforcing load of binary particles (carbon and alumina) in the binary matrix of polypropylene (PP)/poly ethylene-co-vinyl acetate (EVA). The samples were prepared through the melt blending and hot pressing technique. Compared to pure PP/EVA matrix, the nanocomposites showed a shift in Fourier-transform infrared spectroscopy peak and absorption intensity, which proves better interaction of nanoparticles with the matrix. The Scanning Electron Microscopy analysis showed the nanocomposite having carbon (C) and alumina (A) relative ratio 2:3 offered even structure with better distribution of nanoparticles compared to other nanocomposites. Also, Differential scanning calorimetry and Thermogravimetric analysis revealed that alumina-rich binary nanoparticles reinforced composites offer an efficient improvement in thermal behavior. Moreover, the nanocomposite containing high alumina relative ratio (C: A = 2:3) gives a sharp shift in thermal conductivity of 1.57 W/m-k from 1.2 W/m-k of carbon-rich nanocomposite (C: A = 3:2) and 0.16 W/m-k of pure PP/EVA. However, these relative properties emphasize the important role of this nanocomposite as a programmable thermal material.     

Highly robust and transparent flexible cover window films based on UV-curable polysilsesquioxane nano sol

Flexible cover window films based on the ultraviolet-curable polysilsesquioxane are prepared to have enhanced mechanical, optical properties, and bending performance. To figure out the factors determining those properties, post–treatment conditions are varied into the light source, temperature, and relative humidity. Then, the effect of such variables is examined in respect of surface hardness, yellow index (YI), and bending cycle reliability of flexible hard coating. Also, the effect of photoinitiator type in terms of their chemical structure is also investigated. Notably, the relative humidity and thermal treatment are more effective to enhance the mechanical properties rather than light exposure. Indeed, compared to that of reference condition, the cover windows treated with 99% relative humidity and thermal aging at 85°C exhibit improved surface hardness by 24.4 and 19.5%, respectively. However, only the relative humidity is rather effective to enhance the optical properties such as the YI by lowering to the most 2.6. The YI is also improved by varying the chemical structure of the photoinitiator. By virtue of post–treatment and a different photoinitiator, we could achieve flexible cover window films with bending reliability at bending radius of 3 mm for 100,000 cycles, showing good mechanical and optical properties simultaneously.     

Nanostructured star‐shaped polythiophene with tannic acid core: Synthesis,characterization, and its physicochemical properties

For the first time, synthesis and characterization of a nanostructured star‐shaped polythiophene (PTh) with tannic acid core by both chemical and electrochemical oxidation polymerization methods through a “core‐first” method is reported. The chemical structures of all samples as representatives were characterized by means of Fourier transform infrared (FTIR), and ¹H nuclear magnetic resonance (NMR) spectroscopies. The electroactivity behaviors of the synthesized samples were verified under cyclic voltammetric conditions, and their conductivities were determined using the four‐probe technique. The synthesized star‐shaped PTh showed higher electrical conductivity and electroactivity than those of the PTh in both chemical and electrochemical polymerized samples, due to its large surface area, spherical, and three‐dimensional structure. Moreover, the thermal behaviors, optical properties, and morphologies of the synthesized samples were investigated by means of thermogravimetric analysis (TGA), ultraviolet–visible (UV–Vis) spectroscopy, and field emission scanning electron microscopy (FE‐SEM), respectively. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43513.     

Preparation and characterization of a novel positively charged nanofiltration membrane based on polysulfone

The goal of this study was to prepare positively charged nanofiltration (NF) membranes to remove cations from aqueous solutions. A composite NF membrane was fabricated by the modification of a polysulfone ultrafiltration support. The active top layer was formed by the interfacial crosslinking polymerization of poly(ethylene imine) (PEI) with p‐xylene dichloride (XDC). Then, it was quaternized by methyl iodide (MI) to form a perpetually positively charged layer. The chemical and morphological changes of the membrane surfaces were studied by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy. To optimize the membrane operation, the PEI solution concentration, PEI coating time, XDC concentration, crosslinking time, and MI concentration were optimized. Consequently, high water flux (5.4 L m^?2 h^?1 bar^?1) and CaCl₂ rejection (94%) values were obtained for the composite membranes at 4 bars and 30°C. The rejections of the NF membrane for different salt solutions, obtained from pH testing, followed the order Na₂SO₄ < MgSO₄ < NaCl < CaCl₂. The molecular weight cutoff was calculated by the retention of poly(ethylene glycol) solutions with different molecular weights, and finally, the stoke radius was calculated as 1.47 nm. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41988.     

Sol–gel preparation of ultralow refractive index silica coatings with hydroxypropyl‐beta‐cyclodextrin as porogen

Ultralow refractive index films were prepared based on a base‐catalyzed sol–gel process using methyltriethoxysilane (MTES), tetraethylorthosilicate (TEOS) as co‐precursors, and hydroxypropyl‐beta‐cyclodextrin (HPCD) as porogen. After further modification by hexamethylisilazane (HMDS), the lowest refractive index of these silica coatings obtained from the hybrid sol was 1.05 and the static water contact angles of the coatings increased from 66.4° to 128.7°. The effect of weight ratio of HPCD to SiO₂ on the refractive index and on the formation of coating films were systematically studied. The data showed that the films prepared with HPCD as porogen got a pore diameter around 4 nm. Compared with those templates such as poloxamer (F127), HPCD not only perform well in decreasing the refractive index of films, but also eliminate light scattering caused by mesopore of the film, will have potential value in the field of surfactant‐templated methods. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44686.     

Preparation and characterization of thermosensitive beads with macroporous structures

Thermosensitive copolymers of poly(N‐isopropyl acrylamide)‐co‐2‐hydroxyethyl methacrylate (NIPA‐co‐HEMA) macroporous resins were synthesized in the form of beads by inverse suspension polymerization. The copolymerization was carried out in aqueous solutions of the comonomers dispersed by cyclohexane with stabilizers. A series of resins with different molar ratios of NIPA : HEMA, and different crosslinking degrees was obtained. The compositions of the copolymers were determined by elemental analysis. The results showed that the content of HEMA in a copolymer was higher than that of the corresponding feed mixture from which the copolymer was made. IR spectra also confirmed the structure of the copolymers. The porous parameters such as true densities, apparent densities, pore volumes, and porosities of the resins were measured by means of pycnometry. The determination of equilibrium swelling ratios and measurement of differential scanning calibration indicated that the resins exhibited thermosensitivity in aqueous solutions. Finally, the loading of hydroxyl groups was determined by titration. The resins have potential applications as supports in solid‐phase synthesis after being functionalized. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1792–1797, 2004