Synthesis of polyaniline/MCM‐41 composite through surface polymerization of aniline

Polyaniline (PANI)/porous silica MCM‐41 (MCM‐41) composite was synthesized according to surface polymerization theory, and it was confirmed through comparing with PANI/solid silica (SiO₂) by TGA and XPS techniques. The morphology and composition of the composite were also characterized by some techniques such as small‐angle XRD, N₂‐adsorption isotherm, SEM, FTIR, and UV–vis. The thermal stability for the PANI/MCM‐41 composite was enhanced when compared with that of pure PANI. With the increase in the concentration of HCl, the doping degree increased and UV‐absorption peak at about 700 nm showed a red shift. The conductivity of the composite was enhanced by increasing the concentration of HCl. The results of FTIR showed that there was a strong interaction between PANI and MCM‐41. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2088–2094, 2006     

Rapid synthesis of homogeneous titania-silica composite with high-BET surface area

We rapidly synthesized a homogeneous titania-silica composite with properties desired by the paper and paint industries by the sol-gel method in a controlled manner. The composite was synthesized by impregnating TiOCl₂ (titania precursor) into preformed silica networks (SiO₂ trimers). The first step before the formation of high molecular weight polymers in this rapid, versatile, and reproducible method involves the generation of trimers of SiO₂ after the rapid condensation of silicic acid monomers. The latter were formed as a product of the reaction of aqueous sodium silicate solution (SiO₂/Na₂O = 3.24) with 2 N HCl. In the second step, TiOCl₂ was added to the SiO₂ trimers at 50 °C. The structure of the composite was characterized by FE-SEM, EDS, TEM, XRD, FTIR, and nitrogen physisorption studies. The results demonstrated the homogeneous incorporation of titania into silica, which is normally difficult to perform because of the significant differences between the hydrolysis rates of the precursors. The maximum BET surface area, average diameter of the pores, and the maximum pore volume obtained were 739 m²/g, 27.4 Å, and 0.29 cm³/g respectively. The composite has superior oil absorption (240 ml/100 g) compared to that of the conventional pure TiO₂ (100 ml/100 g) filler. It also shows significant photocatalytic ability. The materials prepared via the proposed method are potential candidates for large scale commercial production.     

Effect of HPC-PANI/SIO2 Emulsion Nanocomposite in Poly(vinyl acetate) for Corrosion-Resistant Coatings

Emulsion nanoparticles of polyaniline were synthesized in an aqueous solution using ammonium persulfate as an oxidant in the presence of nanometer-size SiO₂ and hydroxylpropylcellulose as a stabilizer. Different concentrations of prepared nanocomposites were blended with poly(vinyl acetate) as the major matrix and coated on the carbon steel. The product was characterized and compared by (XRD), (FTIR), (SEM), and (TEM). According to the results 1 wt.% of HPC-PANI/SiO₂ nanocomposite in PVAc has a much lower corrosion current in NaCl solution and 3 wt.% of HPC-PANI/SiO₂ nanocomposite in PVAc has the best corrosion protection in HCl.     

Water-based chlorination treatment of SBS rubber soles to improve their adhesion to waterborne polyurethane adhesives in the footwear industry

Solutions of trichloroisocyanuric acid (TCI) in different organic solvents are commonly employed in the footwear industry to improve the adhesion of SBS (styrene-butadiene-styrene) rubber soles to polyurethane adhesive. To avoid the use of organic solvents in the chlorinating solutions, several water-based chlorinating treatments were investigated in this study: (i) inorganic chlorine compounds (HCl-acidified sodium hypochlorite solution; free active chlorine (FAC) = 47.8 g/l); (ii) organic chlorine donors (aqueous solution of 3 wt% TCI/H₂O, and ethanol solutions of 3 wt% HD (1,3-dichloro-5,5-dimethylhydantoine), or NCS (N-chlorosuccinimide); (iii) organic chlorine donor salts (aqueous solutions containing 3 wt% DCI (sodium dichloro isocyanurate), CB (chloramine B, N-chloro-sodium-phenylsulphenamide), or CT (chloramine T, N-chloro-sodium-p-toluenesulphenamide). The surface modifications produced by treatment of SBS rubber with the aqueous chlorinating agents were compared with those obtained by using the current solvent-based chlorinating treatment (3 wt% TCI/MEK). The FAC concentration and the chlorine stability in the solutions were determined by iodine titration, and the SBS rubber surface pH was determined with a flat pH probe. The surface modifications on the SBS rubber were analyzed by ATR-IR spectroscopy, XPS, contact-angle measurements and SEM. The adhesion properties were evaluated by T-peel strength tests on treated SBS rubber/waterborne polyurethane adhesive/roughened leather joints. The failed surfaces obtained after peel tests were analyzed by ATR-IR spectroscopy to precisely assess the locus of failure of the adhesive joints. The nature of the modifications produced on the SBS rubber surface depended on the chlorinating system used, the SBS rubber surface pH value, and the free active chlorine concentration of the chlorinating solution. The most effective chlorinating agents were TCI/H₂O and HD/EtOH, but they were not stable over time due to quick chlorine evolution. Treatment with NaClO/HCl and DCI/H₂O provided acceptable adhesive strength values although there was fast chlorine evolution in the NaClO/HCl solution; the free active chlorine concentration in the DCI/H₂O solution was stable for at least 4 days after preparation. Finally, the treatment with NCS/EtOH, CB/H₂O and CT/H₂O did not chemically modify the SBS rubber surface, so the adhesion to polyurethane adhesive was not improved.     

PES/SiO2 nanocomposite by in situ polymerization: Synthesis,structure, properties,and new applications

SiO₂ nanoparticles of a quantum size (15 nm or less) were prepared via sol–gel method using tetraethylorthosilicate as a precursor. SiO₂ nanoparticles were characterized by X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FESEM) analyses. Polyethersulfone/silica (PES/SiO₂) crystal structure nanocomposite was prepared by in situ polymerization using silica nanoparticles as reinforcement filler. The polymerization reaction was done at 160°C in paraffin bath in the presence of diphenolic monomers. XRD and FESEM analyses were used to study the morphology of the synthesized nanocomposite. The purity and thermal property of the PES/SiO₂ nanocomposite were studied by energy dispersion of X‐ray analysis and differential scanning calorimetry, respectively. The effect of silica particles on the hydrophilicity of PES/SiO₂ nanocomposite was also investigated. It was showed that the PES/SiO₂ nanocomposite had a higher swelling degree when compared with the pure PES. The synthesized PES/SiO₂ powder was used to remove Cu(II) ions from its aqueous solution. The effect of experimental conditions such as pH, shaking time, and sorbent mass on adsorption capacity of PES/SiO₂ nanocomposite were investigated. It was found that incorporation of a low amount of silica (2 wt%) into the polymer matrix caused the increase of the Cu(II) ions adsorption capacity of PES. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Doped polyaniline in Brønsted acid ionic liquid 1‐butyl‐3‐methylimidazolium bis[trifluoromethyl(sulfonyl)]imide/bis[trifluoromethyl(sulfonyl)]imide

We report the preparation and characterization of doped polyaniline (PANI) in an ionic liquid 1‐butyl‐3‐methylimidazolium bis[trifluoromethyl(sulfonyl)]imide (BMImTFSI) medium. Aniline monomer was chemically polymerized via oxidation with KMnO₄ in an ionic liquid BMImTFSI solution containing a monoprotic Brønsted acid bis[trifluoromethyl(sulfonyl)]imide (HTFSI). HTFSI is the source of proton that doped PANI. The identity of PANI as the reaction product was confirmed with both ultraviolet–visible and Fourier transform infrared spectra. Unlike syntheses in aqueous media, the doped PANI did not readily precipitate from the ionic liquid; a transparent and stable green solution‐like liquid dispersion was obtained (dispersion is used to refer the product hereafter). PANI precipitated when dedoped with organic bases such as triethylamine. The PANI precipitate can be redoped by HCl and the so‐doped PANI has conductivity of about 2.0 × 10^?2 S/cm. The liquid dispersion of doped PANI in the ionic liquid can be diluted by many organic solvents or other ionic liquids to diluted “solutions.” © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Organic coatings containing polyaniline and inorganic pigments as corrosion inhibitors

Polyaniline (PANI) was synthesized by chemical oxidative polymerization in laboratory conditions. The main objective was to study the properties of organic coatings containing PANI and PANI in combination with other anti-corrosive pigments. The adhesion, barrier, and anti-corrosion properties of the coatings containing PANI and selected chemically active pigments were studied as well as the combination of PANI with zinc dust. Epoxy resin of bisphenol type hardened with a polyamine-based curing agent was used as a binder. In order to examine the synergic effect of PANI and anti-corrosion pigment in epoxy coatings, Zn₃(PO₄)₂·2H₂O with an acidic aqueous extract, Ca₃(BO₃)₂ with a basic aqueous extract and SrCrO₄ with a neutral aqueous extract have been tested.     

Effects of the interaction between siloxane hydrolysate and PANI on the properties of PANI/SiO2 hybrid materials

PANI/SiO₂ Hybrids were synthesized via a sol‐gel process using tetramethoxysilane (TMOS), γ‐glycidoxypropyltrimethoxysilane (GPTMS), and 3‐(trimethoxysily1)propyl methacrylate (MSMA) as precursors, respectively. The effect of the interaction between siloxane hydrolysate and PANI on the microstructure and properties of the PANI/SiO₂ Hybrid Materials was studied using scanning electron microscopy, Fourier‐transform infrared, UV–vis, ¹H NMR, thermo gravimetric analysis, and potentiodynamic polarization analysis. Experiment results demonstrated that, an appropriate interaction between siloxane hydrolysate and PANI is useful to achieve a homogeneous and stable hybrid. The weak interaction between silanols and PANI will cause the phase separation between siloxane hydrolysate and PANI, whereas the strong interaction may lead to the formation of bulk materials and precipitation. In comparison with TMOS and MSMA, more hydrogen bonds are formed in the PANI/SiO₂ hybrid materials using GPTMS as precursor, which make it have a homogeneous and smooth surface without detectable cracks and present excellent corrosion protection properties. POLYM. COMPOS., 38:657–662, 2017. © 2015 Society of Plastics Engineers     

Preparation and evaluation of polyaniline and polypyrrole modified water‐dispersible conducting nanocomposites of polyacrylonitrile with silica

Water‐dispersible conducting nanocomposites were prepared by precipitating polyaniline (PANI)/polypyrrole (PPY) in an aqueous suspension of polyacrylonitrile–SiO₂ (PAN–SiO₂) via K₂CrO₄–NaAsO₂ redox polymerization. Incorporation of PANI and PPY in the composites was confirmed by the FTIR spectrum. Scanning electron microscopic analyses for the PANI–(PAN–SiO₂) and PPY–(PAN–SiO₂) composites indicated formation of lumpy aggregates with irregular sizes. TEM analyses revealed formation of spherical particles with size ranging between 80 and 150 nm for PANI–(PAN–SiO₂) nanocomposite and 75–150 nm for PPY‐(PAN‐SiO₂) nanocomposites, respectively. Thermal stabilities of the PANI–(PAN–SiO₂) and PPY–(PAN–SiO₂) nanocomposites were higher than those of the individual base polymers. Conductivity values of PANI–(PAN–SiO₂) nanocomposite (10^?3 S cm^?1) and PPY–(PAN–SiO₂) nanocomposite (10^?4 S cm^?1) were remarkably improved relative to that for PAN homopolymer (>10^?11 S cm^?1). Both of these composites produced a permanently stable aqueous suspension when the polymerization was conducted in presence of nanodimensional SiO₂ as a particulate dispersant. Copyright © 2004 Society of Chemical Industry     

The role of polyaniline salts in the removal of direct blue 78 from aqueous solution: A kinetic study

Three polyaniline salts (PANI–H₂SO₄, PANI–H₃PO₄, and PANI–HNO₃) have been synthesized by chemical oxidative polymerization of aniline. They have been tested as adsorbents for the removal of the textile dye direct blue 78 (DB78) from aqueous solution. The interaction followed pseudo-second-order kinetics whether the rate of interaction was measured from the depletion of dye concentration in solution or the increase in the amount of dye adsorbed on the PANI surface. The removal rate was a function of the activity of the polymer as well as the reaction parameters of the polymer/dye system. The activity of the PANI depended on the polymerization conditions. These conditions involve the concentration of aniline, ammonium peroxydisulfate as oxidant, and sodium dodecylsulfate (SDS), the type of dopant acid (H₂SO₄, H₃PO₄, HNO₃), and the polymerization time. Higher removal rate was observed at oxidant/aniline mole ratio equals 1. The rate of removal was in the order PANI–H₃PO₄ > PANI–H₂SO₄ > PANI–HNO₃. The rate decreased with increasing the concentration of DB78 and pH. It increased with increasing the load of PANI. Pseudo-second-order kinetics, external surface adsorption, and intraparticle diffusion models were concurrently operating in the removal of DB78 with PANI.     

A study on the electrochromic properties of polyaniline/silica composite films with an enhanced optical contrast

A polyaniline (PANI)/silica (SiO₂) composite film was prepared by a simple in situ electrodeposition method, and its electrochromic (EC) properties were studied. When PANI was electrodeposited in the presence of SiO₂ particles, the resulting PANI/SiO₂ composite films possessed higher surface areas, larger redox charge capacities, and higher doping levels, thus enhanced optical contrasts. By incorporating SiO₂ particles into the PANI film, the transmittance change at 700 nm from 10.7% to 16.4%, or an enhancement of ca. 50%, was achieved when operating between −0.5 V and 0 V. In addition, x-ray photoelectron spectroscopy (XPS) indicated that the formation of the highly oxidized PANI might have been retarded through the addition of SiO₂ particles. Furthermore, the growth mechanism of the PANI/SiO₂ composite film was proposed.     

Electrospun silk fibroin/PAN double-layer nanofibrous membranes containing polyaniline/TiO<Subscript>2</Subscript> nanoparticles for anionic dye removal

In the present study, novel silk fibroin (SF)/polyacrylonitrile (PAN) double-layer nanofilters defined by a variable composition of polyaniline (PANI)/TiO₂ nanoparticles were prepared using an electrospinning technique, and their application for dye removal was investigated. Scanning electron microscopy (SEM) showed that fibrous mats characterized by nanoscale diameters (70–120 nm) and random ultrafine fiber orientations without beads were successfully obtained. Tensile test results revealed that the strength and Young’s modulus were markedly enhanced in the hybrid double-layer SF-PAN membranes relative to single-layer polymers. In addition, the incorporation of PANI/TiO₂ nanoparticles within the hybrid samples resulted in a notable increase in strength and modulus. The adsorption-assisted nanofiltration performance of the membranes in removing anionic reactive black (HFGR) dye from aqueous solution was investigated using a dead-end stirred cell filtration device. The effect of several variables, including PANI/TiO₂ nanoparticle content, pH and dye concentration, were evaluated. Hybrid nanofilters containing 7.5 wt% PANI/TiO₂ nanoparticles demonstrated excellent dye removal efficiency of up to ~92% in acidic solution.     

Preparation of PANI–PVA composite film with good conductivity and strong mechanical property

The polyaniline (PANI)–polyvinyl alcohol (PVA) conductive composite films [doped with hydrochloride (HCl), dodecylbenzene sulphonic acid and amino sulphonic acid (NH₂SO₃H) aqueous solution] were synthesised by ‘in situ’ polymerisation, and their conductivities were compared. Among these composite films, HCl–PANI–PVA composite film possessed the highest conductivity that reached 1360?S·m^??1 [w_(PVA)?=?40%]. Meanwhile, the effects of PVA content, HCl concentration, oxidant ammonium persulphate (APS) dosage, reaction time and film drying temperature on tensile strength of the HCl–PANI–PVA composite films were studied. The tensile strength of the film was improved greatly due to effective mixture of PANI and PVA. When the PVA content was 40%, C_(HCl)?=?1.0?mol·L^??1, reaction time was 4.0?h, n_(APS)/n_(aniline)?=?1.0 and film drying temperature was 80°C, and the tensile strength of the HCl–PANI–PVA composite film reached the maximum of 60.8?MPa. At the same time, the structure of composite materials was characterised and analysed through ultraviolet spectrum and SEM.     

Physical and adsorptive characterizations of immobilized polyaniline for the removal of methyl orange dye

Synthesized polyaniline (PANI) powder mixed with ENR-PVC polymer blend adhesive was immobilized on glass plates for the adsorption of methyl orange (MO) dye. The immobilized PANI composite was made up of plasticized PANI aggregates and was in a doped state. The incorporation of ENR-PVC blend in PANI slightly reduced the surface area from 9.2 to 8.5 m² g^-1, and its presence was confirmed through FTIR. The adsorption process was highly dependent on the aeration rate, and the pH of MO solution in which 40 mL min^-1 and ambient pH (6.5) was selected as the working conditions. The process of MO uptake onto the immobilized PANI obeyed the pseudo-second-order kinetic model, while intra-particle diffusion was found to dominate the adsorption process. The q_m of the immobilized PANI was 77.3 mg g^-1 for MO uptake and obeyed the Freundlich isotherm model. The thermodynamic study revealed that the adsorption process of immobilized PANI was spontaneous and unfavorable at high temperature. The immobilized PANI was found to be comparable with other PANI based adsorbents in term of cost, recyclability and adsorption efficiency.     

Ion-crosslinked carboxymethyl cellulose/polyaniline bio-conducting interpenetrated polymer network: preparation,characterization and application for an efficient removal of Cr(VI) from aqueous solution

A simple, cheap, and environmentally friendly bio-conducting interpenetrated polymer blend network was prepared and introduced as a highly efficient system with suitable physical and mechanical properties for industrial removal of toxic Cr(VI) ions from aqueous solution. Carboxymethyl cellulose/polyaniline (CMC/PANI) interpenetrated network (IPN) blend was prepared by simple simultaneous ion-cross-linking of CMC and PANI chains using Al³⁺ cations. The CMC/PANI bio-conducting nanocomposite was characterized using X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy equipped with an "energy dispersive X-ray spectroscopy" (SEM–EDX) technique. The CMC/PANI blend, ion-cross-linked by Al³⁺ cations, showed good stability and high surface area, proper for the removal of toxic Cr(VI) ions of the aqueous solution. Batch removal experiments were accomplished and the impression of effective variables including solution pH, initial concentration of Cr(VI) ions, contact time, and adsorbent dosage were checked and optimized. The outcome of our findings revealed that the removal of Cr(VI) ions by CMC/PANI nanocomposite IPN strongly depends on solution pH. The removal information was matched with the Langmuir adsorption isotherm model and the utmost monolayer adsorption capacity at pH 2 was 136.98 mg/g at 25 °C. The pseudo-second-order kinetics were operated and the thermodynamic parameters suggested spontaneous and exothermic nature of the adsorption process. Consequences indicated that CMC/PANI nanocomposite IPN could be an affective eco/environmentally friendly adsorbent for the removal of Cr(VI) ions from aqueous solutions.

     

Electrosynthesis of Polyaniline/SiO2 Composite at high pH in the Absence of Extra Supporting Electrolyte

Summary Electropolymerization of aniline was investigated in solutions of different pH from 1.0 to 12.1 without extra supporting electrolyte. FT-IR Spectra of the polymers display characteristic absorptions for polyaniline (PANI) including that for protonated PANI, although some of the polymers were obtained in solutions of high pH. PANI obtained from acidic solutions displayed the usual electroactivities in 0.5 mol·l^-1 H₂SO₄, while those obtained from solutions of pH 6.0 to 12.1 showed an unusual redox pair additionally on cyclic voltammograms at 0.04 V vs. SCE. This redox pair can be ascribed to the redox of phenazine ring, originated from the attack of nitrenium cation to PANI chain in the ortho-position. Electrocodeposition of PANI and SiO₂ was conducted through electrophoresis of silica particles towards anode as aniline anodically electropolymerized. Energy dispersive X-ray diffraction (EDX) analysis and SEM inspection were performed on obtained PANI/SiO₂ to investigate the composite film.     

Superfine structure,physical properties,and dyeability of alkaline hydrolyzed soly(ethylene terephthalate)/silica nanocomposite fibers prepared by in situ polymerization

In this study, poly(ethylene terephthalate) (PET)/SiO₂ nanocomposites were synthesized by in situ polymerization and melt‐spun to fibers. The superfine structure, physical properties, and dyeability of alkaline hydrolyzed PET/SiO₂ nanocomposite fibers were studied. According to the TEM, SiO₂ nanoparticles were well dispersed in the PET matrix at a size level of 10–20 nm. PET/SiO₂ nanocomposite fibers were treated with aqueous solution of sodium hydroxide and cetyltrimethyl ammonium bromide at 100°C for different time. The differences in the alkaline hydrolysis mechanism between pure PET and PET/SiO₂ nanocomposite fibers were preliminarily investigated, which were evaluated in terms of the weight loss, tensile strength, specific surface area, as well as disperse dye uptake. PET/SiO₂ nanocomposite fibers showed a greater degree of weight loss as compared with that of pure PET fibers. More and tougher superfine structures, such as cracks, craters, and cavities, were introduced, which would facilitate the certain application like deep dyeing. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3691–3697, 2006     

Effect of LiCl as an additive in the polymerization reaction of aniline and its influence on the structural and electrical property of polyaniline

Doped polyaniline (PANI) is synthesized in aqueous HCl medium by ammonium persulphate (APS) as oxidant. We used LiCl during in situ polymerization of aniline to explore any improvement of electrical properties of PANI due to Li⁺ and HCl incorporation. We varied the HCl and LiCl molarity in the polymerization medium keeping the total Cl⁻ concentration constant. The level of Li⁺ loading was measured by fluorescence spectroscopy of doped PANI. The PANI was characterized by FTIR and UV–visible spectroscopy, XRD analysis, intrinsic viscosity measurement and optical microscopy. The conductivity of doped PANI was measured by four probe method. Hall effect measurement was also done to measure the resistivity and the charge carrier density of the doped polyaniline.     

Synthesis and characterization of ferromagnetic polyaniline with conductivity in an applied magnetic field

Ferromagnetic polyaniline (PANI) with conductivity was synthesized with peroxydisulfate as an oxidant and horseradish peroxidase as a catalyst in an N′‐a‐hydroxythylpiperazine‐N′‐ethanesulfanic acid buffer solution containing aniline, HCl, and NiCl₂·6H₂O in an applied magnetic field. The result of an electron paramagnetic resonance spectrum indicated that there were unpaired electrons in the resulting product, the spin density of which was 7.60 × 10¹⁹ spins/g. The curve of the magnetization versus the magnetic field showed that PANI had soft ferromagnetic behavior at about 300 K. The saturation magnetization and coercive force of PANI were 0.033 emu/g and 5 Oe, respectively. Ultraviolet–visible and Fourier transform infrared spectra indicated that there was interaction between Ni²⁺ and PANI chains but the structure of the backbone chains of PANI synthesized in the presence of a magnetic field hardly changed compared with that of PANI synthesized without NiCl₂·6H₂O. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

A new smart coating of polyaniline–SiO2 composite for protection of mild steel against corrosion in strong acidic medium

Organic coating approaches for corrosion protection with inherently conducting polymers have become important because of restriction on the use of heavy metals and chromates in coatings due to their environmental problems. The present work is directed towards the synthesis of polyaniline (PANI) and polyaniline–SiO₂ composites (PSCs) by chemical oxidation polymerization in the presence of phosphoric acid and evaluation of synthesized PANI and PSCs for protection of mild steel from corrosion in a strong aggressive medium (i.e. 1.0 mol L^–1 HCl). A suitable coating with PSC was formed on mild steel using epoxy resin by the powder coating technique. A comparative study of the corrosion protection efficiency of mild steel coated with PANI and PSC in 1.0 mol L^–1 HCl solution was evaluated using the Tafel extrapolation, chrono‐amperometry and weight loss methods. The PSC coating showed that a significant reduction in the corrosion current density reflects the better protection of mild steel in an acidic environment. Higher protection efficiency up to 99% was achieved by using PSC‐coated mild steel at 6.0 wt% loading of PSC in epoxy resin. The coating performance and corrosion rate of mild steel were investigated by using immersion of polymer‐coated mild steel in 1.0 mol L^–1 HCl for 60 days and indicated that PSC‐coated mild steel showed better performance from corrosion than PANI in an acidic medium.© 2012 Society of Chemical Industry