Transparent dispensible high‐refractive index ZrO2/epoxy nanocomposites for LED encapsulation

In this study, we report a facile ex situ approach to preparing transparent dispensible high‐refractive index ZrO₂/epoxy nanocomposites for LED encapsulation. Highly crystalline, near monodisperse ZrO₂ nanoparticles (NPs) were synthesized by a nonaqueous approach using benzyl alcohol as the coordinating solvent. The synthesized particles were then modified by (3‐glycidyloxypropyl)trimethoxysilane (GMS) ligand. It was found that, with tiny amount of surface‐treating ligand, the modified ZrO₂ NPs were able to be easily dispersed in a commercial epoxy matrix because of the epoxy compatible surface chemistry design as well as the small matrix molecular weight favoring mixing. Transparent thick (1 mm) ZrO₂/epoxy nanocomposites with a particle core content as high as 50 wt % and an optical transparency of 90% in the visible light range were successfully prepared. The refractive index of the prepared composites increased from 1.51 for neat epoxy to 1.65 for 50 wt % (20 vol %) ZrO₂ loading and maintained the same high‐Abbe number as the neat epoxy matrix. Compared with the neat epoxy encapsulant, an increase of 13.2% in light output power of red LEDs was achieved with the 50 wt % ZrO₂/epoxy nanocomposite as the novel encapsulant material. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3785–3793, 2013     

Preparation and properties of polythiourethane/ZnS nanocomposites with high refractive index

The inorganic–organic crosslinking polythiourethane/ZnS (PTU/ZnS) nanocomposites with high refractive index and transmittance were successfully prepared. The thiol‐capped ZnS nanoparticles with a diameter of about 5 nm were fabricated into the molecular chains of PTU via the formed covalent bonds between the capped ZnS and the matrix. The investigations demonstrated the ZnS nanoparticles were uniformly dispersed in the PTU matrix even at high contents. The optical studies showed the refractive index of the highly transparent nanocomposite films linearly increased from 1.643 to 1.792 with the increase of the ZnS content. The structure, morphology, and other properties were also characterized by FTIR, NMR, AFM, XRD, DSC, TGA, etc. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of novel ZnS/sulfur-containing polymer nanocomposite optical materials with high refractive index and high nanophase contents

A series of novel transparent bulk ZnS-polymer nanocomposites with high refractive index were successfully prepared via in-situ bulk polymerization in the presence of 2-mercaptoethanol (ME)-capped ZnS NPs. The polymerization mechanism combined the step-growth and free radical polymerization of different monomers of episulfide, m-xylylene diisocyanante (XDI), 2-hydroxyethyl methacrylate (HEMA) and N,N-dimethylacrylamide (DMAA). The high refractive index of episulfide compounds, including ESGMES, ESDGEBA and MPS, were synthesized and used as monomers in polymerization systems. The cured nanocomposites with 30 wt% nanoparticles show high refractive index and good transparency. The refractive index of the nanocomposites could be continuously regulated in the range from 1.59 to 1.65 by the content of ZnS NPs and the pencil hardness is round about 5H. The content of ME-ZnS NPs can affect the thermal stability, mechanical and optical properties of the resulting nanocomposites, and the relationship between them were studied by TGA, DMA, pencil hardness test, Charpy impact test.     

Nanocomposite films of poly(vinylidene fluoride) filled with polyvinylpyrrolidone‐coated multiwalled carbon nanotubes: Enhancement of β‐polymorph formation and tensile properties

To improve interactions between carbon nanotubes (CNTs) and poly(vinylidene fluoride) (PVDF) matrix, multiwalled CNTs (MWCNTs) were successfully coated with amphiphilic polyvinylpyrrolidone (PVP) using an ultrasonication treatment performed in aqueous solution. It was found that PVP chains could be attached noncovalently onto the nanotubes' surface, enabling a stable dispersion of MWCNTs in both water and N,N‐dimethylformamide. PVP‐coated MWCNTs/PVDF nanocomposite films were prepared by a solution casting method. The strong specific dipolar interaction between the PVP's carbonyl group (C?O) and the PVDF's fluorine group C?F₂ results in high compatibility between PVP and PVDF, helping PVP‐coated MWCNTs to be homogenously dispersed within PVDF. Fourier transform infrared and X‐ray diffraction characterization revealed that the as‐prepared nanocomposite PVDF films exhibit a purely β‐polymorph even at a very low content of PVP‐wrapped MWCNTs (0.1 wt%) while this phase is totally absent in the corresponding unmodified MWCNTs/PVDF nanocomposites. A possible mechanism of β‐phase formation in PVP‐coated MWCNTs/PVDF nanocomposites has been discussed. Furthermore, the tensile properties of PVDF nanocomposites as function of the content in PVP‐coated MWCNTs were also studied. Results shows that the addition of 2.0 wt% of PVP‐coated MWCNTs lead to a 168% increase in Young's modulus and a 120% in tensile strength. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Thermal and optical properties of hyperbranched fluorinated polyimide/mesoporous SiO2 nanocomposites exhibiting high transparency and reduced thermo-optical coefficients

A series of hyper-branched polyimide (HBPI)/mesoporous SiO₂ nanocomposite films were prepared from a fluorinated anhydride (6FDA), a fluorinated triamine (TFAPOB), and mesoporous SiO₂ nanoparticles (NPs). The anhydride-terminated precursor of HBPI was functionalized using a coupling agent prior to mixing with SiO₂ NPs. The morphologies and thermal-optical properties of the nanocomposite films were investigated, with particular focus on their optical transparency, refractive indices (n), and thermo-optical (TO) coefficients. The absolute values of TO coefficients (|dn/dT|) of HBPI film (50.8 ppm/K) were significantly reduced to 13.4 ppm/K by homogeneous dispersion of 15 wt% of SiO₂ NPs. The HBPI/SiO₂ composite films exhibited high thermal stability without significant weight loss of up to 400 °C in air. The films also exhibited small coefficients of linear thermal expansion (CTEs) within the range 30–40 ppm/K. In addition, enhanced interfacial interactions between SiO₂ and HBPI significantly improve the optical transparency with cutoff wavelengths shorter than 450 nm. The refractive indices of HBPI/SiO₂ composite films were found to range from 1.477 to 1.502, which agrees well with the calculated values. This study shows that the incorporation of SiO₂ NPs in multi-functional HBPI matrix is a promising approach to prepare high performance thermally stable films for thermo-optic applications.     

High strength nanocomposite hydrogels with outstanding UV‐shielding property

A novel series of nanocomposite hydrogels (TAD gels) with high mechanical strength and excellent UV‐shielding property were prepared by in situ free‐radical copolymerization of acrylamide (AM) and N,N‐dimethylacrylamide (DMAA) in aqueous solutions of TiO₂ nanoparticles (TiO₂ NPs). It was found that the TiO₂ NPs were uniformly dispersed in the copolymer matrix and acted as inorganic crosslinking agents in TAD gels owing to their hydrogen bonding interactions with polymer chains. The TAD gels exhibited excellent mechanical properties such as large elongations at break, high elastic moduli, and ultimate stresses, all of these properties as well as swelling ratios of TAD gels could be easily controlled by changing the AM ratios and TiO₂ contents in the initial solutions. In addition, the TAD gels with low AM ratios could be prepared into thin films in a customized Teflon model and these films showed high transparency in visible light but could completely block the UV light with wavelength below 366 nm and prevent the methylene blue from degradation under UV irradiation. POLYM. COMPOS., 37:810–817, 2016. © 2014 Society of Plastics Engineers     

Synthesis and characterization of ZnS/hyperbranched polyester nanocomposite and its optical properties

The ZnS/hyperbranched polyester nanocomposite with higher refractive index was prepared by incorporating the acrylated 2-(2-mercapto-acetoxy)-ethyl ester-capped ZnS nanoparticles into the acrylated Boltorn™ H20 (H20). The acrylated 2-(2-mercapto-acetoxy)-ethyl ester-capped colloidal ZnS nanoparticles were synthesized by the reaction of zinc acetate with thioacetamide in N,N-dimethylformamide. The acrylated hyperbranched polyester was obtained by reacting acryloyl chloride with hydroxyl group of H20. The acrylated H20 plays an important role in stabilizing and dispersing ZnS nanoparticles with a diameter of 1-4 nm. The refractive indices of ZnS/hyperbranched polyester nanocomposites, depending on ZnS content, were determined to be in the ranges of 1.48-1.65.     

Preparation and characterization of TiO2 and polymer nanocomposite films with high refractive index

Novel nanocomposite films of TiO₂ nanoparticles and hydrophobic polymers having polar groups, poly (bisphenol‐A and epichlorohydrin) or copolymer of styrene and maleic anhydride, with high refractive indices, high transparency, no color, solvent‐resistance, good thermal stability, and mechanical properties were prepared by incorporating surface‐modified TiO₂ nanoparticles into polymer matrices. In the process of preparing colloidal solution of TiO₂ nanoparticles, severe aggregation of particles can be reduced by surface modification using carboxylic acids and long‐chain alkyl amines. These TiO₂ nanoparticles dispersed in solvents were found not to aggregate after mixing with polymer solutions. Transparent colorless free‐standing films were obtained by drying a mixture of TiO₂ nanoparticles colloidal solution and polymer solutions in vacuum. Transmission electronic microscopic studies of the films suggest that the TiO₂ nanoparticles of 3–6 nm in diameter were dispersed in polymer matrices while maintaining their original size. Thermogravimetric analysis results indicate that the nanocomposite film has good thermal stability and the weight fraction of observed TiO₂ nanoparticles in the film is in good accordance with that of theoretical calculations. The refractive index of nanocomposite films of TiO₂ and poly(bisphenol‐A and epichlorohydrin) was in the range of 1.58–1.81 at 589 nm, which linearly increased with the content of TiO₂ nanoparticles from 0 to 80 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Physicochemical and antibacterial properties of chitosan‐polyvinylpyrrolidone films containing self‐organized graphene oxide nanolayers

Chitosan films have a great potential to be used for wound dressing and food‐packaging applications if their physicochemical properties including water vapor permeability, optical transparency, and hydrophilicity are tailored to practical demands. To address these points, in this study, chitosan (CS) was combined with polyvinylpyrrolidone (PVP) and graphene oxide (GO) nanosheets (with a thickness of ～1 nm and lateral dimensions of few micrometers). Flexible and transparent films with a high antibacterial capacity were prepared by solvent casting methods. By controlling the evaporation rate of the utilized solvent (1 vol % acidic acid in deionized water), self‐organization of GO in the polymer matrix was observed. The addition of PVP to the CS/GO films significantly increased their water vapor permeability and optical transmittance. A blue shift in the optical absorption edge was also noticed. Thermal analysis coupled with Fourier transform infrared spectroscopy suggested that the superior thermal stability of the nanocomposite films was due to the formation of hydrogen bonds between the functional groups of chitosan with those of the graphene oxide. An improved bactericidal capacity of the nanocomposite films against gram‐positive Staphylococcus aureus and gram‐negative Escherichia coli bacteria was also observed. Highly flexible, transparent (opacity of 6.95), and antimicrobial CS/25 vol % PVP/1 wt % GO films were prepared. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43194.     

Fabrication of highly refractive barium‐titanate‐incorporated polyimide nanocomposite films with high permittivity and thermal stability

Crystalline nanoparticles of barium titanate (BT) are incorporated into polyimide (PI) to fabricate highly refractive, anti‐UV‐degradable nanocomposite films with high permittivity and thermal stability. For homogeneous incorporation of BT nanoparticles into the PI matrix, the BT nanoparticles are surface modified by phthalimide with the aid of a silane coupling agent as a scaffold. The PI nanocomposites are prepared by in situ polymerization in which a diphthalic anhydride and a diamine are used to form the PI matrix in the presence of the surface‐modified nanoparticles. The refractive index of the transparent nanocomposite films reaches 1.85 at a nanoparticle content of 59 vol% with a high dielectric constant of ε = 37 and thermal stability up to 460 °C. Copyright © 2012 Society of Chemical Industry     

Antibacterial activities of novel nanocomposite biofilms of chitosan/phosphoramide/Ag NPs

Novel nanocomposite films of chitosan/phosphoramide/Ag NPs were prepared containing 1–5% of silver nanoparticles. The Ag NPs were synthesized according to the citrate reduction method. The XRD and SEM analysis of Ag NPs, chitosan (CS), phosphoramide (Ph), CS/Ph, CS/Ag NPs films and the nanocomposite films 1–5 containing CS/Ph/1–5% Ag NPs were investigated. The in vitro antibacterial activities were evaluated against four bacteria including two Gram‐positive Staphylococcus aureus (S. aureus), Bacillus cereus (B. cereus) and two Gram‐negative Escherchia coli (E. coli), Pseudomonas aeruginosa (P. aeruginosa) bacteria. Results revealed greater antibacterial effects of the films against Gram‐positive bacteria. Also, nanocomposite films containing higher percent of Ag NPs showed more antibacterial activities. POLYM. COMPOS. 36:454–466, 2015. © 2014 Society of Plastics Engineers     

Click chemistry‐assisted preparation and properties of phosphorus and nitrogen synergistic flame retardant optical resin with a high refractive index

In this study, halogen‐free flame retardant tri(acryloyloxyethyl) phosphate (TAEP) was prepared using 2‐hydroxyethyl acrylate and phosphorus oxychloride. The chemical structure of TAEP was characterized by Fourier transform infrared and proton nuclear magnetic resonance spectrometers. The mixture of TAEP, acrylamide, and pentaerythritol tetrathioglycolate with different P, N, and S content were used to prepare flame retarding optical resin via the click chemistry curing. The curing performance, thermal stability, and flame retardant performance of the optical resins were measured by differential scanning calorimeter, thermogravimetric analyzer, vertical burning tester, and limiting oxygen index test, respectively. Additionally, the morphology of the burned residual was investigated by scanning electronic microscopy, and the refractive indices of the optical resins were measured by an Abbe Refractometer. The results strongly indicated that increasing sulfur content in resins improved their refractive indices, but deteriorated their flame retardancy. Meanwhile, the nitrogen element was helpful for the flame retardancy of the optical resin. With S N, and P contents of 3.00%, 1.00%, and 6.70 wt %, respectively, the refractive index of the optical resin reached up to 1.4987, and its flame retardancy achieved the UL‐94 V‐0 level and the LOI value of 29.3%. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46648.     

Bio‐nanocomposite films based on cellulose nanocrystals filled polyvinyl alcohol/chitosan polymer blend

Bio‐nanocomposite films based on polyvinyl alcohol/chitosan (PVA/CS) polymeric blend and cellulose nanocrystals (CNC) were prepared by casting a homogenous and stable aqueous mixture of the three components. CNC used as nanoreinforcing agents were extracted at the nanometric scale from sugarcane bagasse via sulfuric acid hydrolysis; then they were characterized and successfully dispersed into a PVA/CS (50/50, w/w) blend to produce PVA/CS–CNC bio‐nanocomposite films at different CNC contents (0.5, 2.5, 5 wt %). Viscosity measurement of the film‐forming solutions and structural and morphological characterizations of the solid films showed that the CNC are well dispersed into PVA/CS blend forming strong interfacial interactions that provide an enhanced load transfer between polymer chains and CNC, thus improving their properties. The obtained bio‐nanocomposite films are mechanically strong and exhibit improved thermal properties. The addition of 5 wt % CNC within a PVA/CS blend increased the Young's modulus by 105%, the tensile strength by 77%, and the toughness by 68%. Herein, the utilization of Moroccan sugarcane bagasse as raw material to produce high quality CNC has been explored. Additionally, the ability of the as‐isolated CNC to reinforce polymer blends was studied, resulting in the production of the aforementioned bio‐nanocomposite films with improved properties. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42004.     

Fumed SiO2 nanoparticle reinforced biopolymer blend nanocomposites with high dielectric constant and low dielectric loss for flexible organic electronics

In the present study, fumed silica (SiO₂) nanoparticle reinforced poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) blend nanocomposite films were prepared via a simple solution‐blending technique. Fourier transform infrared spectroscopy (FTIR), ultraviolet–visible spectroscopy (UV–vis), X‐ray diffraction (XRD), and scanning electron microscopy (SEM) were employed to elucidate the successful incorporation of SiO₂ nanoparticles in the PVA/PVP blend matrix. A thermogravimetric analyzer was used to evaluate the thermal stability of the nanocomposites. The dielectric properties such as dielectric constant (?) and dielectric loss (tan δ) of the PVA/PVP/SiO₂ nanocomposite films were evaluated in the broadband frequency range of 10^?2 Hz to 20 MHz and for temperatures in the range 40–150 °C. The FTIR and UV–vis spectroscopy results implied the presence of hydrogen bonding interaction between SiO₂ and the PVA/PVP blend matrix. The XRD and SEM results revealed that SiO₂ nanoparticles were uniformly dispersed in the PVA/PVP blend matrix. The dielectric property analysis revealed that the dielectric constant values of the nanocomposites are higher than those of PVA/PVP blends. The maximum dielectric constant and the dielectric loss were 125 (10^?2 Hz, 150 °C) and 1.1 (10^?2 Hz, 70 °C), respectively, for PVA/PVP/SiO₂ nanocomposites with 25 wt % SiO₂ content. These results enable the preparation of dielectric nanocomposites using a facile solution‐casting method that exhibit the desirable dielectric performance for flexible organic electronics. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44427.     

Preparation and characterization of polynorbornene/sepiolite hybrid nanocomposite films

Polynorbornene/sepiolite hybrid nanocomposite films were prepared using polynorbornene dicarboximide and modified sepiolite with 3‐ aminopropyltriethoxysilane (3‐APTES). Exo‐N‐(3,5‐dichlorophenylnorbornene)‐5,6‐dicarboxyimide (monomer) and their copolymers were synthesized via ring‐opening polymerization using ruthenium catalysts. Subsequently, the surface‐modified sepiolite by 3‐APTES was mixed with the polynorbornene copolymers to prepare hybrid nanocomposite films. The modified sepiolite particles were well dispersed in N,N‐dimethylacetamide and distributed randomly throughout the polynorbornene matrix in the hybrid films, which enhanced the dimensional stability and mechanical and oxygen barrier properties of the polynorbornene/sepiolite hybrid nanocomposite films. © 2014 Society of Chemical Industry     

Graphene oxide reinforced chitosan/polyvinylpyrrolidone polymer bio‐nanocomposites

Bio‐nanocomposite films based on chitosan/polyvinylpyrrolidone (CS/PVP) and graphene oxide (GO) were processed using the casting/evaporation technique. It has been found that the three components of bio‐nanocomposites can be easily mixed in controlled conditions enabling the formation of thick films with high quality, smooth surface and good flexibility. Structural and morphological characterizations showed that the GO sheets are well dispersed in the CS/PVP blend forming strong interfacial interactions that provide an enhanced load transfer between polymer chains and GO sheets thus improving their properties. It has been found that the water resistance of the CS/PVP blend is improved, and the hydrolytic degradation is limited by addition of 0.75 and 2 wt % GO. The modulus, strength, elongation and toughness of the bio‐nanocomposites are together increased. Herein, the steps to form new bio‐nanocomposite films have been described, taking the advantage of the combination of CS, PVP and GO to design the aforementioned bio‐nanocomposite films, which allow to have extraordinary properties that would have promising applications as eventual packaging materials. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41042.     

Effect of Cesium Aluminate Nanofiller on Optical Properties of Polyvinyl Pyrrolidone Nanocomposite Films

The nanocomposite films of poly vinylpyrrolidone (PVP) with different amounts viz., 2, 4, 6 and 8?wt% of cesium aluminate (CsAlO₂) have been fabricated using solvent casting technique. The effect of nanofiller content on the optical properties of PVP/CsAlO₂ nanocomposite films has been established by UV-visible spectroscopy. The UV-visible transmittance studies revealed that the UV light absorbing nature of nanocomposite films with considerable visible transparency. The Fourier Transform Infrared (FTIR) spectral studies visualizes the effect of CsAlO₂ nanofiller on the structural behaviors of PVP, while optical studies reveals an obvious change in the electronic band structure leading to a significant reduction in optical band gaps. The scanning electron microscopic (SEM) studies establish the morphological changes in PVP matrix upon doping with CsAlO₂. The measured refractive index (RI) depends on the volume fraction of CsAlO₂ nanofiller and the result indicates that a substantial increase of RI values from 1.85 to 2.64 at wave length 360 nm. The dielectric studies, optical conductivity measurements and Urbach energy analysis also supports the dopant dependent optical property, tuning of PVP/CsAlO₂ nanocomposite films to enable effective material property engineering to suit specified application requirements.     

Self-cleaning antireflected surfaces based on treated PEO/SiO2 nanocomposite films

In this study, the polyethylene oxide (PEO)/SiO₂ nanoparticles (NPs) nanocomposite films with various SiO₂ NPs concentrations were prepared using an in situ formation of NPs in the polymer matrix for self-cleaning antireflected surface applications. The effect of SiO₂ NPs in PEO/SiO₂ NPs nanocomposite films on the structural, morphological, chemical, thermal, optical, and electrical properties of PEO/SiO₂ NPs nanocomposite films was performed. According to the x-ray diffraction and the differential scanning calorimetry analysis, the crystallinity degree of the nanocomposite films decreases by increasing the SiO₂ NPs concentrations. The bandgap energy of PEO/SiO₂ NPs nanocomposite films decreases from 3.95 to 3.55 eV as the SiO₂ NPs concentration increases up to 10 wt.%. The average electrical conductivity of the PEO/SiO₂ NPs nanocomposite films increases from 5.1 × 10⁻⁷ to 2.0 × 10⁻⁶ S/cm as the SiO₂ NPs concentration increases up to 10 wt.%. The refractive index decreases to 1.64 at 550 nm for the PEO/SiO₂ NPs nanocomposite films with 10 wt.% of SiO₂ NPs, and the water contact angle decreases to around 0° after thermal treatment, which confirms that the PEO/SiO₂ NPs nanocomposite films can be used as self-cleaning antireflected surfaces.     

Characteristics of waterborne polyurethane/poly(N‐vinylpyrrolidone) composite films for wound‐healing dressings

For ideal wound‐healing dressings, a series of waterborne polyurethane (WBPU)/poly(N‐vinylpyrrolidone) (PVP) composite films (transparent film dressings) were prepared by in situ polymerization in an aqueous medium. Stable WBPU/PVP composites, which had a high remaining weight greater than 98.4%, were obtained. The maximum content of PVP for stable WBPU/PVP dispersions was found to be about 15 wt %. The water absorption (%) and equilibrium water content (%) of the WBPU/PVP composite films remarkably increased in proportion to the PVP content and the time of water immersion. The maximum water absorption and equilibrium water content of the WBPU/PVP composite films were in the range of 21–158 and 22–56%, respectively. The water vapor transmission rate of the WBPU/PVP composite films was in the range of 1816–2728 g/m²/day. These results suggest that WBPU/PVP composite films may have high potential as new wound‐dressing materials that provide and maintain the moist environment needed to prevent scab formation and dehydration of the wound bed. By a wound‐healing evaluation using a full‐thickness rat model experiment, it was found that a wound covered with a typical WBPU/PVP composite film (15 wt % PVP) was completely filled with new epithelium without any significant adverse reactions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008