Research on Preparation,Structure and Properties of TiO2/Polythiourethane Hybrid Optical Films with High Refractive Index

Hybrid optical films of TiO₂‐triethoxysilane‐capped polythiourethane (TCPTU) with high refractive indices have been prepared via an in situ sol‐gel method. The high refractive index triethoxysilane‐capped polythiourethane (TCPTU) was synthesized by polyaddition of the triethoxysilane‐modified trimercaptothioethylamine (TMTEA) and 2,2′‐dimercaptoethylsulfide (MES) with 2,4‐tolylene diisocyanate (TDI). The titania content in the hybrid films can be adjusted from 0 to 80 wt.‐% by the feed ratio of titania precursor [Ti(OBu)₄] to polymer (TCPTU). Both FTIR and DSC analyses indicate that there is chemical bonding between the titania domain and the polymer chain. TGA results suggest that the titania of high content was successfully incorporated into polymer matrices and this series of hybrid films have good thermal properties. AFM measurements indicate that in the hybrid films the titania domains are of nanosize scale and the domain size averagely decreases from 60–80 nm to 5–20 nm with increasing content of titania, and the variation of surface roughness for the hybrid films has the same trend. These may be relative to the content of TCPTU and the interaction between titania and polymer (TCPTU). The refractive indices of the hybrid films at 632.8 nm increased from 1 632 to 1 879 as the titania content varied from 0 to 80 wt.‐%.

AFM image of the hybrid film.     

The research on syntheses and properties of novel epoxy/polymercaptan curing optical resins with high refractive indices

A novel thioether glycidyl resin bis[3-(2,3-Epoxypropylthio)phenyl]-sulfone (BEPTPhS) with high refractive index was synthesized by condensation of bis(3-mercaptophenyl)sulfone (BMPS) with epichlorohydrin. It's structure was characterized by FTIR, MS and NMR. It was the first time that trimercaptothioethylamine (TMTEA) was used as curing agent to cure epoxy resins. Optical resins possessing high refractive index were prepared by curing diglycidyl ether of bisphenol A (DGEBA) with the mixture of TMTEA and ethylendiamine (EDA) and by curing BEPTPhS/DGEBA with TMTEA. The research on the optical properties of resins of DGEBA cured by the mixtures of TMTEA and EDA indicated that these resins possess higher refractive index (n_d>1.60), lower dispersity (ν_d>34), high impact strength (IPS>30 kJ m⁻²) and higher transmittance. The n_d, ν_d and density of these resins varied linearly with the EDA content in the curing agent mixtures. The optimum ratio of the EDA content to that of TMTEA is 20:80 (molar ratio), at this ratio the cured resin has the optimum optical properties (n_d²⁰=1.61, v_d=35.4). The cured resins of BEPTPhS/TMTEA have a high refractive index (the highest is n_d=1.67). The optical, physical and thermal properties of the cured optical resins of BEPTPhS/TMTEA were discussed in this paper.     

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.

     

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%.     

TiO2 nanoceramic films prepared by ion beam assisted evaporation for optical application

A TiO₂ nanoceramic film was prepared as an alternative absorber layer for infrared thermal detectors. The TiO₂ film was amorphous, and its grain size increased with the ion anode voltage and oxygen flow rate. Moiré deflectometry was applied for measuring the nonlinear refractive indices of TiO₂ films on polycarbonate (PC) substrates. The nonlinear refraction index was measured to be of the order of 10⁻⁸ cm² W⁻¹ and the change in refractive index was of the order of 10⁻⁵. The linear refractive index was correlated with the porosity. Denser TiO₂ films exhibited higher linear refractive indices, obvious red-shifts and narrower absorption bands in the near-IR region.     

Characterization of antireflective coatings on poly(methyl methacrylate) substrate by different process parameters

The high/low refractive index organic/inorganic antireflective (AR) hybrid polymers were formed using the sol–gel process, in which TiO₂/2‐hydroxyethyl methacrylate (2‐HEMA) (high refractive index hybrid polymer) and SiO₂/2‐HEMA (low refractive index hybrid polymer) two‐layer thin films were formed on a hard coating deposited poly(methyl methacrylate) (HC‐PMMA) substrate by both spin coating and dip coating. The relationship between the process parameters and the optical properties, thickness, porosity, surface morphology, and adhesion was determined. The results show that the reflectance of the two‐layer thin films on HC‐PMMA substrate is less than 0.21% (λ = 550 nm), with good adhesion (5B) and a hardness of up to 4H. In addition, the thickness, porosity, and roughness of the films affect refractive index and the antireflection properties of the AR two‐layered thin film. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO₂/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO₂ sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO₂ and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO₂ and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO₂/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO₂/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO₂/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.     

N-type silk fibroin/TiO2 nanocomposite transparent films: electrical and optical properties

This paper highlights the effect of different concentrations of titanium dioxide (TiO₂) nanoparticles on the electrical and optical properties of silk fibroin (SF). TiO₂ based SF nanocomposite films were prepared using the solvent casting method. Uniform dispersion and agglomeration of nanoparticles, in nanocomposite films, were observed by field emission SEM. The conductivity of pure SF and nanocomposite films was determined by a four-point probe and the TiO₂ nanoparticles were found to bring high conductivity to the nanocomposite films. Dielectric strength improved with the addition of nanoparticles to the SF matrix. Dielectric constant and capacitance of the pure SF and nanocomposite films were measured using an LCR meter, which showed a 10-fold enhancement on the addition of nanoparticles in SF. A very unusual property, i.e. negative resistance, was observed during LCR meter analysis for the nanocomposite films for a particular range of frequency (200–550 kHz), voltage (1 V) and current (0.5–1.5 μA). TiO₂ nanoparticles changed the semiconducting behavior of the SF films from p-type to n-type as measured by the Hall effect experiment. The optical properties of pure SF and nanocomposite films were measured using a UV–visible spectrophotometer. The increased concentration of nanoparticles in the SF has effectively enhanced the absorbing coefficient, refractive index and percentage transmittance and reduced the bandgap energy. These SF/TiO₂ nanocomposite films have shown the potential to be used as dielectric and high refractive index material for optoelectronics applications. © 2021 Society of Industrial Chemistry.     

A synergistic effect of nano‐Tio2 and graphite on the tribological performance of epoxy matrix composites

The influence of incorporated 300 nm TiO₂ (4 vol %), graphite (7 vol %), or combination of both fillers on the tribological performance of an epoxy resin was studied under various sliding load (10–40 N) and velocity conditions (0.2–3.0 m/s). Mechanical measurements indicated that the incorporation of TiO₂ significantly enhanced the flexural and impact strength of the neat epoxy and the graphite including epoxy. Tribological tests were conducted with a cylinder‐on‐flat testing rig. The incorporation of nano‐TiO₂ significantly improved the wear resistance of the neat epoxy under mild sliding conditions; however, this effect was markedly diminished under severe sliding conditions (high velocity and normal load). Nano‐TiO₂ reduced the coefficient of friction only under severe sliding conditions. Graphite showed a beneficial effect in reducing the wear rate and the coefficient of friction of the neat epoxy. Compared to the nano‐TiO₂‐filled epoxy, the graphite‐filled epoxy showed more stable wear performance with the variation of the sliding conditions, especially the normal load. A synergistic effect was found for the combination of nano‐TiO₂ and graphite, which led to the lowest wear rate and coefficient of friction under the whole investigated conditions. The synergistic effect was attributed to the effective transfer films formed on sliding pair surfaces and the reinforcing effect of the nanoparticles. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2391–2400, 2006     

Preparation and properties of a high-entropy amorphous oxide with high refractive index by containerless solidification

A non-proportional high-entropy oxide glass disc: 25LaO_3/2-25TiO₂–25NbO_5/2-(25-x) WO₃-xZrO₂(x = 0, 5, 10) was formed using containerless solidification technology. In optical tests, the 25LaO_3/2-25TiO₂–25NbO_5/2-20WO₃–5ZrO₂(x = 5) disc had the highest refractive index (2.53) and the highest visible transmittance (84%). In addition, the refractive index of amorphous materials prepared from La₂O₃, TiO₂, Nb₂O₅, WO_3, and ZrO₂ were all greater than 2.1, which is considered as a high refractive index. The results suggest that these components can provide a specific reference for optical glass material selection in future research.Furthermore, based on the concept of performance synergy in high-entropy materials, our research group developed a high-entropy amorphous oxide in equal proportion, 20LaO_3/2-20TiO₂–20NbO_5/2-20WO₃–20ZrO₂ (Qi Xiwei, 2019). The structure has a high refractive index (2.22) and a high Abbe coefficient (61), which ensures that the lens has sufficient clarity when it is ultra-thin. By comparing the results of the two systems, we found that all non-proportional high-entropy systems are unable to simultaneously show both a high Abbe value and a high refractive index. This phenomenon further indicates the necessity of preparing high-entropy amorphous oxide in equal proportion.     

Fabrication of functionally graded nano‐TiO2‐reinforced epoxy matrix composites

Functionally graded nano‐TiO₂ epoxy matrix composites were successfully fabricated using a centrifugal method. In the preparation of the composite, the aggregation of nano‐TiO₂ occurred during curing, which had a negative effect on the composite performance. To solve this problem, we introduced a silane coupling agent to modify the surface of the nano‐TiO₂, thereby improving the performance and mechanical properties simultaneously. The modified nano‐TiO₂ (s‐TiO₂) had better dispersion in the epoxy resin, making it possible to produce depth gradients of the mechanical properties of functionally graded materials (FGMs). The s‐TiO₂ was characterized with respect to functional groups, morphology, and chemical elements using transmission electron microscopy, X‐ray photoelectron spectroscopy, and Fourier‐transform infrared spectroscopy. The results show that a silane layer was successfully coated on the surface. Also, the gradients of the mechanical and permittivity properties of the FGM indicated that by modifying the surface of the nano‐filler, it is possible to fabricate nano‐filler‐reinforced epoxy matrix FGMs using a centrifugal method. POLYM. COMPOS., 35:557–563, 2014. © 2013 Society of Plastics Engineers     

In situ solvothermal synthesis and characterization of transparent epoxy/TiO2 nanocomposites

A solvothermal process was developed to in situ prepare epoxy (EP)/TiO₂ hybrid precursors. The chemical structure of samples was confirmed by X-ray and Fourier transformed infrared spectroscopy. Field emission scanning electron microscope micrographs of cured EP/TiO₂ hybrid composites showed that well-dispersed TiO₂ nanoparticles were successfully in situ formed in epoxy matrix through the solvothermal process. The thermogravimetic analysis, DSC, and gel content measurements showed that EP/TiO₂ hybrid precursors were fully cured with the glass transition temperature decreasing gradually. The effect of TiO₂ contents on optical and surface properties was investigated in detail. The results indicated that epoxy/TiO₂ nanocomposites exhibited excellent UV shielding effect and high visible light transparency. The contact angle of EP/TiO₂ nanocomposites, when the content of silane-coupling agent (KH560) was 5 g and the content of tetrabutyl titanate (TBT) was 3 g, can reach as high as 101°, which was 36° higher than that of pure EP, representing for the increase of hydrophobicity. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and properties of polystyrene–γ‐methacryloxypropyl trimethoxy silane copolymer/zirconia nanohybrid materials

Polystyrene (PS)–γ‐methacryloxypropyl trimethoxy silane (MPTMS) copolymer/zirconia (ZrO₂) nanohybrid materials were successfully prepared by the combination of solvothermal and in situ synthesis methods, in which the comonomer was used as chemical bonding agent between the nanoparticles and the matrix, and acetylacetone (AcAc) was used as a size control agent of ZrO₂ in the PS matrix. Then, a new transparency film with a relatively high refractive index (1.72) was successfully obtained, in which ZrO₂ could be dispersed well in the PS–MPTMS matrix. Field emission scanning electron microscopy images indicated that AcAc was helpful in the dispersion of the nanoparticles, and smaller ZrO₂ particles with no aggregation were obtained in the PS–MPTMS matrix. The structure and thermal properties of the hybrid films were investigated by Fourier transform infrared spectroscopy and thermogravimetric analysis, and the surface properties were also examined. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2320–2327, 2013     

Effect of the Amount of H2O on the Crystallization of TiO2 Films Prepared from Alkoxide Solutions Containing Acetylacetone

Sol–gel‐derived TiO₂ films were prepared by dip‐coating from Ti(OC₃H₇ⁱ)₄–CH₃COCH₂COCH₃–HNO₃–H₂O–C₂H₅OH solutions, and the effect of the H₂O content in solutions on the crystallization of TiO₂ films during the heat treatment at 800°C was discussed. The crystalline phase, crystallite size, grain size, and refractive index of the TiO₂ films depended on the H₂O/Ti(OC₃H₇ⁱ)₄ mole ratios (x) in the coating solutions. Highly dense and crystalline rutile films were obtained at x = 0.5–10, where the crystallites and grains became larger with increasing x. The further increase in x from 10 to 50 reduced the crystallite size and refractive index of the films, where anatase phase appeared at x = 30–50.     

The interfacial effect of TiO2–Ag core–shell micro‐/nanowires on poly(arylene ether nitrile)

Novel TiO₂–Ag core–shell micro‐/nanowires (TiO₂ shell coating on Ag core) have been successfully prepared via a solvent–thermal method. Energy dispersive spectroscopy and X‐ray diffraction analyses revealed that the micro‐/nanowires were composed of Ag, Ti and O elements, and Ag was face‐centered cubic whereas TiO₂ was mainly amorphous. Interestingly, scanning electron microscopy (SEM) and transmission electron microscopy results showed that most of the TiO₂ bristles were perpendicular to and uniformly studded on the surface of the Ag cores. Subsequently, TiO₂–Ag/poly(arylene ether nitrile) (PEN) composite films were prepared via a solution‐casting method in order to investigate the effect of TiO₂–Ag on the PEN matrix. SEM images showed that there was good interfacial adhesion between fillers and PEN matrix owing to the special bristle‐like structure. Thermal analysis results showed that the TiO₂–Ag/PEN composite films possessed excellent thermal properties endowed by the PEN matrix. The dielectric constant of the composite films increased to 9.3 at 100 Hz when the TiO₂–Ag loading reached 40 wt%. Rheology measurements revealed that the network formed by TiO₂–Ag was sensitive to shear stress and nearly time independent. © 2013 Society of Chemical Industry     

Refractive materials for interlayer optical contacts with TiO2‐based organic/inorganic hybrids

Organic/inorganic hybrid materials were prepared by synthesizing from titanium tetraisopropoxide (TTIP), diethanolamine (DEOA), and water. Formulating the materials with thermosetting polymers, the composites were designed for refractive optical contacts with heat lamination of a film having >50 μm thickness. Inherent difficulties of TiO₂ and sol‐gel reaction of TTIP, i.e. photocatalytic properties and prompt sol‐gel reaction to form large TiO₂ particle, were avoided by stabilizing Ti with use of DEOA. The reactivity of the sol‐gel reaction and formation of TiO₂ crystal structure were suppressed by DEOA. However, suppression of the photocatalytic properties was not enough and needed a use of anti‐oxidant agent, 2,6‐di‐t‐butyl‐p‐cresol (BHT). The titanium‐based organic/inorganic hybrid materials and its epoxy composites were transparent in visible wavelength region and gave in the range of 1.66 to 1.73 of refractive indices depending on stoichometric parameters of TTIP, water, and DEOA for the hybrid materials. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Properties and microstructures of epoxy resin/TiO2 and SiO2 hybrids

Epoxy resin/TiO₂ and epoxy resin/SiO₂ hybrids were prepared by different procedures, and their mechanical properties were correlated to their microstructures, as indicated by small‐angle X‐ray scattering (SAXS) measurements. Epoxy resin/TiO₂ hybrids were prepared by mixing the epoxy resin (EP828) with N‐(2‐aminoethyl)‐3‐aminopropyltrimethoxysilane (S320) in acetone, and then titanium‐n‐butoxide (TnBU) was added. In addition, epoxy/SiO₂ hybrids were prepared by mixing EP828 with a curing agent, a diamino heterocyclic compound (B002) in acetone, and an organo silica sol (silica nanoparticles dispersed in methylethylketone) was added. In the EP828/S320/TiO₂ hybrid systems, the TiO₂ component was attached to both of the chain ends of the epoxy matrix, hence leading to the formation of inorganic domains via the covalent bonds. SAXS profiles of these hybrids showed peaks at q = 2.3 nm^?1, caused by interference between the domains. The storage modulus increased with increasing TiO₂ content above the T_g, owing to the strong interactions between TiO₂ and the epoxy matrix. The tanδ peak position did not change, although the intensity decreased with increasing TiO₂ content. The SAXS profiles of the EP828/B002/SiO₂ hybrids were very different to those of the corresponding EP828/S320/TiO₂ hybrids, and indicated that SiO₂ particles with rough surfaces were randomly dispersed in the epoxy matrix. The storage moduli of the EP828/B002/SiO₂ hybrid systems increased only slightly with SiO₂ content, because of the weak interactions. These mechanical properties are well explained by the microstructures derived from the SAXS profiles. Copyright © 2004 Society of Chemical Industry     

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     

Preparation and properties of TiO2‐filled poly(acrylonitrile‐butadiene‐styrene)/epoxy hybrid composites

Poly (acrylonitrile‐butadiene‐styrene) (ABS) was used to modify diglycidyl ether of bisphenol‐A type of epoxy resin, and the modified epoxy resin was used as the matrix for making TiO₂ reinforced nanocomposites and were cured with diaminodiphenyl sulfone for superior mechanical and thermal properties. The hybrid nanocomposites were characterized by using thermogravimetric analyzer (TGA), dynamic mechanical analyzer (DMA), universal testing machine (UTM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The bulk morphology was carefully analyzed by SEM and TEM and was supported by other techniques. DMA studies revealed that the DDS‐cured epoxy/ABS/TiO₂ hybrid composites systems have two T_gs corresponding to epoxy and ABS rich phases and have better load bearing capacity with the addition of TiO₂ particles. The addition of TiO₂ induces a significant increase in tensile properties, impact strength, and fracture toughness with respect to neat blend matrix. Tensile toughness reveals a twofold increase with the addition of 0.7 wt % TiO₂ filler in the blend matrix with respect to neat blend. SEM micrographs of fractured surfaces establish a synergetic effect of both ABS and TiO₂ components in the epoxy matrix. The phenomenon such us cavitation, crack path deflection, crack pinning, ductile tearing of the thermoplastic, and local plastic deformation of the matrix with some minor agglomerates of TiO₂ are observed. However, between these agglomerates, the particles are separated well and are distributed homogeneously within the polymer matrix. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013