Polymer nanoparticle-based porous antireflective coating on flexible plastic substrate

Increased using of plastic optical elements has generated a need for applying antireflection coatings onto plastic substrates. In this paper we reported a facile method to preparing porous thin films on plastic substrates by spin-casting poly (methyl methacrylate) (PMMA)/polystyrene (PS) mixed latices, followed by selectively removing PS particles. The refractive index of the porous coating is directly related to its porosity which could be controlled by varying mixing fraction of the sacrificial PS particles. The obtained porous thin films exhibited excellent anti-reflective (AR) performance over visible range with minimum reflection of 0.02%. The powerful control on refractive index and the versatility of this method makes it practicable to prepare antireflective coating on various plastic substrates with optimal performance.     

Synthesis and properties of PMMA‐ZrO2 organic–inorganic hybrid films

In this work we report the synthesis process and properties of PMMA‐ZrO₂ organic–inorganic hybrid films. The hybrid films were deposited by a modified sol‐gel process using zirconium propoxide (ZP) as the inorganic (zirconia) source, methyl methacrylate (MMA) as the organic source, and 3‐trimetoxy‐silyl‐propyl‐methacrylate (TMSPM) as the coupling agent between organic and inorganic phases. The films were deposited by dip coating on glass slide substrates from a hybrid precursor solution containing the three precursors with molar ratio 1 : 0.25 : 0.25 for ZP, TMSPM, and MMA, respectively. After deposition, the hybrid thin films were heat‐treated at 100°C for 24 h. The macroscopic characteristics of the hybrid films such as high homogeneity and high optical transparence evidenced the formation of a cross‐linked, interpenetrated organic–inorganic network. The deposited PMMA‐ZrO₂ hybrid films were homogeneous, highly transparent and very well adhered to substrates. Fourier Transform Infra‐Red measurements of the hybrid films display absorption bands of chemical groups associated with both PMMA and ZrO₂ phases. The amounts of organic and inorganic phases in the hybrid films were determined from thermogravimetric measurements. The surface morphology and homogeneity of the hybrid films at microscopic level were analyzed by scanning electron microscopy and atomic force microscopy images. From the analysis of optical transmission and reflection spectra, the optical constants (refraction index and extinction coefficient) of the hybrid films were determined, employing a physical model to simulate the hybrid optical layers. The refraction index of the hybrid films at 532 nm was 1.56. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42738.     

Fabrication of highly refractive,transparent BaTiO3/poly(methyl methacrylate) composite films with high permittivities

Incorporation of crystalline barium titanate (BT) nanoparticles into poly(methyl methacrylate) (PMMA) was carried out to prepare highly refractive polymer nanocomposite films that have transparency and high permittivities. The BT nanoparticles were prepared by hydrolysis of a barium/titanium complex alkoxide in 2‐methoxyethanol, then surface‐modified with a silane coupling agent (3‐methacryloxypropyltrimethoxysilane) to improve their affinity for PMMA. The incorporation of the surface‐modified nanoparticles into PMMA was performed up to a nanoparticle content almost equivalent to particle close‐packing state. The refractive index of the composite films increased with nanoparticle incorporation, keeping the relative transmittance normalized with PMMA film above 90%. A high refractive index of 1.82 was reached at a nanoparticle content of 53 vol% with a dielectric constant as high as 36 and a dissipation factor as low as 0.05. The results demonstrate that the crystalline BT nanoparticles are useful fillers for effectively increasing both refractive index and dielectric constant of polymer nanocomposites. Copyright © 2011 Society of Chemical Industry     

Preparation of high-refractive-index PMMA/TiO2 nanocomposites by one-step in situ solvothermal method

High-refractive index polymeric materials, which are transparent, have many promising applications in optical design and advanced optoelectronic fabrication. In order to improve the refractive index of polymeric materials, inorganic materials with high-refractive index, such as TiO₂, are always added into polymers. However, some of the traditional synthetic methods are complicated and hard to control. In our work, we developed a novel and simple method, a one-step in situ solvothermal method, to prepare poly(methyl methacrylate) (PMMA) and nano-TiO₂ hybrid films. Methyl methacrylate (MMA), vinyltrimethoxysilane (VTMO), titanium butoxide [Ti(OBu)₄], ethanol, hydrochloric acid, azobis-isobutyronitrile and tetrahydrofuran were added into a reaction vessel altogether and the polymerization of PMMA matrix and the formation of nano-TiO₂ composite carried out simultaneously. To improve the adhesion between PMMA and TiO₂, VTMO was used as a comonomer. The results indicate that TiO₂ nanoparticles produced by decomposition of titanium butoxide are dispersed homogeneously in the PMMA matrix. The size of TiO₂ crystals in PMMA/TiO₂ nanocomposites is about 5–6 nm. The hybrid films have a good transparency (over 80 %) in the visible region, a good thermal stability and a UV-shielding property after the incorporation of TiO₂. The refractive index of as-formed PMMA/TiO₂ nanocomposites increases up to 1.839 at 633 nm as the content of Ti(OBu)₄ is 50.00 wt%.     

Photocontrol of the refractive index of poly(methyl methacrylate) with a nitrone additive

Hydroxy‐substituted aromatic nitrone derivatives were used for the photochemical control of the refractive index of poly(methyl methacrylate) (PMMA) films. Upon irradiation with 366‐nm light in solution, these derivatives underwent rearrangement reactions, which eventually produced N,N‐diarylformamide derivatives in quantitative yields. Similar photoreactions of the aromatic nitrones in the PMMA films lowered the refractive index of the films by as much as 0.014. The magnitude of the observed refractive‐index change was enough for hydroxy‐substituted nitrones to be used as additives for the fabrication of graded‐index‐type polymer optical fibers. In addition, the refractive index of the PMMA films remained almost constant at any conversion of the starting nitrone derivatives for at least 70 days at room temperature. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2517–2520, 2004     

Thermal and optical properties of PMMA–titania hybrid materials prepared by sol‐gel approach with HEMA as coupling agent

A series of sol‐gel derived organic–inorganic hybrid materials consisting of organic poly(methyl methacrylate) (PMMA) and inorganic titania (TiO₂) were successfully synthesized by using 2‐hydroxyethyl methacrylate (HEMA) as coupling agent. In this work, HEMA is first copolymerized with methyl methacrylate monomer at specific feeding ratios by using benzoyl peroxide (BPO) as initiator. Subsequently, the as‐prepared copolymer (i.e., sol‐gel precursor) is then cohydrolyzed with various contents of titanium butoxide to afford chemical bondings to the forming titania networks to give a series of hybrid materials. Transparent organic–inorganic hybrid materials with different contents of titania are always achieved. Effects of the material composition on the thermal stability, optical properties, and morphology of neat copolymer and a series of hybrid materials, in the form of both coating and free‐standing film, are also studied by differential scanning calorimetry, thermogravimetric analysis, UV–Vis transmission spectra, refractometer, and atomic force microscopy, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 400–405, 2004     

Swelling measurement of polymers in high pressure carbon dioxide using a spectroscopic reflectometer

We developed an in situ thickness monitor using a spectroscopic reflectometer to measure the swelling behaviors of polymer thin films in carbon dioxide up to 30 MPa. Because the change in thickness was measured under high-pressure CO₂, the measurement was performed through a sapphire window with a relatively high refractive index. We found that the window effect on the reflectivity can be successfully eliminated. To confirm the accuracy of the analysis, we measured the swelling behaviors of four polymers (poly(methyl methacrylate) (PMMA), polystyrene (PS), poly(n-butyl methacrylate) (PBMA), and poly(dimethylsiloxane) (PDMS)), and compared the swelling measurements with reported data. The swelling ratios of the polymers were in reasonable agreement with literature data. Notably, anomalous swelling was observed for PBMA and PDMS, although anomalous swelling has been observed in films much thinner than those of our samples, probably due to the low glass transition temperatures and high swelling ratios of PBMA and PDMS.     

Synthesis and characterization of organic-inorganic hybrid thin films from poly(acrylic) and monodispersed colloidal silica

Hybrid thin films containing nano-sized inorganic domain were synthesized from poly(acrylic) and monodispersed colloidal silica with coupling agent. The 3-(trimethoxysilyl)propyl methacrylate (MSMA) was bonded with colloidal silica first, and then polymerized with acrylic monomer to form a precursor solution. Then, the precursor was spin coated and cured to form the hybrid films. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results showed that the coverage area of silica particle by the MSMA decreased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. Thus, the silica domain in the hybrid films was varied from 20 to 35 nm by the different mole ratios of MSMA to silica. The results of scanning electron microscope, transmission electron microscope, and elemental analysis support the above results. The prepared hybrid films from the crosslinked acrylic polymer moiety showed much better film uniformity, thermal stability and mechanical properties than the poly(methyl methacrylate) (PMMA) based hybrid materials. Large pin-holes were found in the PMMA-silica hybrid films probably due to the significant difference on thermal properties between the two moieties or the evaporation of solvent. The refractive index decreased linearly with increasing the silica fraction in the hybrid films. Excellent optical transparence was obtained in the prepared hybrid films. These results show that the hybrid thin films have potential applications as passive films for optical devices.     

Optical and physical properties of zirconium dioxide reinforced poly(methyl methacrylate) nanocomposite films

The objective of this study was to investigate the fundamental aspects of acrylic resin and zirconia nanoparticle interaction to analyze the optical properties and subsequent changes in refractive index with incremental loading of nanoparticles. Poly(methyl methacrylate) (PMMA) reinforced with zirconia nanoparticles were prepared by dip coating, spin coating and solvent casting techniques. An overall understanding of the polymer nanocomposite film has been achieved using the spectroscopic and morphological studies. The vital aspect of this whole study is to derive a simple yet an efficient nanocomposite film capable of imparting extraordinary optical properties. Within the limitations of this research a very crucial property of the material has been revealed. The RI as well as the optical transparency of the nanocomposite film has been steadily maintained with a significant increase of RI by the magnitude of 0.06 and ~100% light transmittance on incorporation of pure zirconia nanoparticles into PMMA matrix has been achieved. The best technique found was spin coating as it could yield thin films and better transparency and higher refractive index.     

Synthesis and Optical Properties of Soluble Polyimide/Titania Hybrid Thin Films

Summary: In this study high‐refractive‐index polyimide/titania hybrid optical thin films were successfully prepared using a sol‐gel process combined with spin coating and multistep baking. The hybrid thin films were prepared from a soluble polyimide, a coupling agent, and a titania precursor. Transparent hybrid thin films can be obtained at TiO₂ content as high as 40 wt.‐%. The FE‐SEM results suggest that the TiO₂ particles in the hybrid thin films have diameters in the nanometer range. The thermal decomposition temperatures of the prepared hybrid materials are above those of the respective polyimide except for the highest TiO₂ content hybrids. The refractive indices at 633 nm of the prepared hybrid thin films increase linearly from 1.66 to 1.82 with increasing TiO₂ content. The excellent optical transparency, thermal stability, and tunable refractive index provide the potentials of the polyimide/titania hybrid thin films in optical applications.

     

Atomic force microscopy studies of poly(methyl methacrylate) doped with photoinitiator

Atomic force microscopy has been applied for measuring the nanomechanical characteristics of poly(methyl methacrylate) thin films containing 5% photoinitiator (Irgacure 651). The nanohardness, Young's modulus, and adhesion to AFM tip have been evaluated for the unexposed samples and after UV‐irradiation. Additionally, FTIR spectroscopy and differential scanning calorimetry (DSC) have been applied to explain the observed changes in nanomechanical properties. It was found that the exposure to ultraviolet changed the nanomechanical properties of polymer because of photo‐oxidative degradation and relaxation processes. These studies lead to the conclusion that the applied photoinitiator has no noticeable effect on nanohardness and Young modulus during PMMA irradiation, but efficiently participates in polymer photo‐oxidation increasing the surface hydrophilicity and adhesion to Si₃N₄. Moreover, the initiator hampers the relaxation of PMMA macromolecules, what was proved by DSC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Metalizable Polymer Thin Films in Supercritical Carbon Dioxide

We report an environmentally “green” method to improve adhesion at a polymer/metal interface by using supercritical carbon dioxide (scCO₂). Spun-cast polystyrene (PS) and poly(methyl methacrylate) (PMMA) thin films on cleaned Si wafers were used for this study. Film thicknesses of both polymer films were prepared in the range of 100 Å to 1600 Å. We exposed the films to scCO₂ in the pressure-temperature (P–T) range corresponding to the density-fluctuation ridge, where the excess swelling of both polymer films occurred, and then froze the swollen structures by quick evaporation of CO₂. A chromium (Cr) layer with film thickness of 300–400 Å was deposited onto the exposed film by using an E-beam evaporator. X-ray reflectivity (XR) measurements showed that the interfacial width between the Cr and exposed polymer layers increased by a factor of about two compared with that without exposure to scCO₂. In addition, the large interfacial broadening was found to occur irrespective of the thickness of both polymer films. After the XR measurements, the dewetting structures of the PS/Cr films induced by additional annealing were characterized by using atomic force microscopy, showing improved surface morphology in the exposed films. Contact angle measurements showed that a decrease in interfacial tension with exposure to scCO₂ accompanied the increase in interfacial width.     

Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

Multiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (T_g) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO₂ substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 10⁴ to 10⁶) on T_g, the effect of film thickness on the coefficients of thermal expansion both below and above T_g, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006     

Synthesis and characterization of titanium dioxide optical films by sol–gel processes

The main purpose of this study is to synthesize the front panel of monitor with a high refractive index optical film. Our experiment uses titanium dioxide nanoparticles mixed with methyl methacrylate (MMA), 2‐hydroxyethyl methacrylate (2‐HEMA), and tri(ethylene glycol) dimethacrylate (TEGDMA) of the wet type and economical sol–gel production process. Our product has a superior mechanical, thermal, and optical properties was demonstrated by Fourier transform infrared spectrum (FTIR), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), UV/visible spectrum, and Spectro Ellipsometer. In addition, we found the surface of the two series of thin film with the organic and inorganic high refractive index (TiO₂) mixed materials, has high transmittance for visible light above 90%, refractive index <1.65 and the hardness test 6H. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2271–2280, 2007     

Abrasion resistance of ceramic thin films of ZrO2/SiO2 on stretched grade polymethyl methacrylate substrates

Abrasion resistance of stretched grade polymethyl methacrylate (PMMA) was increased by using the sol–gel method to have it coated with a ZrO₂/SiO₂ thin film. Different molar ratios of Zr(OPr)₄/Si(OPr)₄ sols were prepared as precursors with propanol. These sols were used for dip-coating the stretched PMMA surfaces to establish very smooth thin films of amorphous Zr–O–Si. Fourier Transform Infrared spectroscopy (FT-IR) was employed to study vibrations of Zr–O–Si bonds within the thin film. The phase analysis was undertaken via X-ray Diffraction (XRD) method. The morphology and thickness of coatings on PMMA were investigated by means of Scanning Electron Microscopy (SEM). The results showed that coating had an amorphous structure with its thickness within the range of 80–100 nm. The water contact angle of PMMA substrates altered from 73° before coating to less than 64° after coating. Once coated, the PMMA substrate had its transparency characteristic (within the UV–vis region) increased. Furthermore, the influences of thermal treatment temperature and molar ratio of precursors (Zr(OPr)₄/Si(OPr)₄) on abrasion resistance of the coatings were studied.     

PMMA‐grafted‐silica/PVC nanocomposites: Mechanical performance and barrier properties

Poly(vinyl chloride) (PVC)/SiO₂ nanocomposites were prepared via melt mixture using a twin‐screw mixing method. To improve the dispersion degree of the nanoparticles and endow the compatibility between polymeric matrix and nanosilica, SiO₂ surface was grafted with polymethyl methacrylate (PMMA). The interfacial adhesion was enhanced with filling the resulting PMMA‐grafted‐SiO₂ hybrid nanoparticles characterized by scanning electron microscopy. Both storage modulus and glass transition temperature of prepared nanocomposites measured by dynamic mechanical thermal analysis were increased compared with untreated nanosilica‐treated PVC composite. A much more efficient transfer of stresses was permitted from the polymer matrix to the hybrid silica nanoparticles. The filling of the hybrid nanoparticles caused the improved mechanical properties (tensile strength, notched impact strength, and rigidity) when the filler content was not more than 3 wt %. Permeability rates of O₂ and H₂O through films of PMMA‐grafted‐SiO₂/PVC were also measured. Lower rates were observed when compared with that of neat PVC. This was attributed to the more tortuous path which must be covered by the gas molecules, since SiO₂ nanoparticles are considered impenetrable by gas molecules. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and characterization of surfactant-induced nanoporous PMMA film

Porous polymer films were prepared by spin-coating of PMMA solutions that contained surfactant (sodium dodecylbenzenesulfonate, NaDDBS) at concentrations higher than the critical micelle concentration, and by selectively removing the water-soluble surfactant molecule in distilled water. After removal of NaDDBS, the nanoporous structure was confined by FE-SEM. The resulting pore size was found to be much smaller than the wavelength of the visible light, and therefore, the nanoporous thin films were optically homogeneous. However, when the film was prepared with 30 wt% porogen loading, the resulting porous film became quite opaque and the refractive index could not be measured. The size and the total volume of the pores in the PMMA film increased with the increase in the porogen concentration. Upon increasing the amount of the surfactant in the film, the refractive index of the nanoporous PMMA film changed from 1.493 to 1.483. The refractive index of the nanoporous polymer film was found to be inversely proportional to the porogen concentration and the pore volume. Transparent PMMA films containing nanoscale pores randomly distributed throughout the film thickness are expected to be versatile in optical applications such as the optical waveguide.     

Organic base‐catalyzed sol–gel route to prepare PMMA–silica hybrid materials

A series of sol–gel‐derived organic–inorganic hybrid materials that comprise organic poly(methyl methacrylate) (PMMA) and inorganic silica (SiO₂) was successfully prepared using aniline as an organic base catalyst to catalyze the sol–gel reactions of tetraethylorthosilicate (TEOS). Aniline was adopted not only as a catalyst but also as a dispersing agent during the preparation of the hybrid materials. The as‐prepared hybrid materials were then characterized using transmission electron microscopy, SEM/energy dispersive X‐ray spectroscopy and Fourier transform infrared spectroscopy. The characteristic temperatures (including T_d and T_g) of the hybrid materials slightly exceeded those of neat PMMA, as revealed from thermogravimetric analysis and differential scanning calorimetry evaluations. Studies of the protection against corrosion demonstrated that the hybrid coatings all improved the protection performance on cold‐rolled steel coupons relative to that of neat PMMA coatings, according to measurements of electrochemical corrosion parameters. Additionally, incorporating silica particles into the polymer may effectively reduce the gas permeability of the polymer membrane. Reducing the size of silica particles (at the same silica feeding) further improved the gas barrier property. Optical clarity studies indicated that introducing silica particles into the PMMA matrix may slightly reduce the optical clarity of the films/membranes, as determined by UV‐visible transmission spectroscopy. The contact angle of H₂O of the hybrid films increased with the amount of aniline. Copyright © 2006 Society of Chemical Industry Society of Chemical Industry     

Synthesis and characterization of high molecular weight metaloquinolate‐containing polymers

In this article, a new method to synthesize novel metaloquinolate (AlQ₃, ZnQ₂)‐containing polymers is reported. A model polymer with 8‐hydroxyquinoline ligands can be obtained by free‐radical copolymerization with methyl methacrylate (MMA), then metaloquinolate (AlQ₃, ZnQ₂)‐containing polymers are prepared by coordinating reaction with di(8‐hydroxyquinoline) aluminum (AlQ₂) chelates or mono (8‐hydroxyquinoline) zinc (ZnQ) chelates without crosslinking. The structures of products are confirmed by NMR, FTIR, ultraviolet‐visible, elementary analysis, photoluminescence spectrum, and gel permeation chromatography analysis. They are soluble in common solvents and suitable to form films. The use of AlQ₂ and ZnQ avoided the crosslinking caused by the AlQ₃, ZnQ₂ formation between different polymer chains. Different from the traditional small organic molecules in organic light‐emitting diodes (OLEDs) fabrication, the polymer can be processed by spin coating without phase separation. Compared to the PMMA or MMA‐co‐HEMA‐CH₂‐Hq, the T_g of the metaloquinolate‐containing polymers was much higher. It should be of interest for OLED applications. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1945–1952, 2006     

Synthesis,characterization, and mechanical property of poly(urethane‐glycidyl methacrylate‐methyl methacrylate) hybrid polymers

Hybrid particles of polyurethane (PU) containing a number of small poly(methyl methacrylate) (PMMA) nanoparticles inside were prepared using glycidyl methacrylate (GMA) monomer as a linker between PU and PMMA; the resulting polymers were poly (urethane‐glycidyl methacrylate‐methyl methacrylate) (PUGM). It was found that the average particle size (D_p) of the PU particles decreased by the inclusion of PMMA particles possibly owing to the low‐solution viscosity of PU. However, D_p of the PUGM hybrid particles increased with increasing the number of covalent bonds between PMMA and PU, which might be due to decreasing the amount of ionic groups per PU chain. Subsequently, the tensile properties of the films made of the PUGM hybrid particles were investigated. It was observed that the modulus of the PU films increased upon the addition of PMMA particle because of a filler effect. In addition, it was seen that the modulus of PUGM hybrid films increased further with increasing the number of covalent bonds. This was attributed to “restricted mobility” of PU chains anchored to the PMMA particles. It was also observed that the tensile strength changed only slightly for PUGM particles, suggesting that the PU matrix was probably responsible for the necking behavior of the films. The elongation of the samples was found to depend on both the presence of covalent bonds between the PMMA particles and PU matrix and the reduced mobility of the PU chains anchored to PMMA particles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011