An electrosprayed coating process for fabricating hemispherical PMMA droplets for an optical diffuser

A modified electrospraying process is proposed for fabricating uniform microsized poly(methyl methacrylate) (PMMA) hemispherical droplets on poly(ethylene terephthalate) films for use as optical diffusers. In this process, an electrode controlled by an electric field is attached to a rotating collector, and various electric field conditions are applied to the droplets ejected from a positively charged nozzle. The distribution of small hemispherical droplets and the surface roughness resulting from this modified electrospraying process are more uniform than those achieved in the normal electrospraying process. The frequency of the field applied to the electrode is not critical to the production of stable PMMA droplets. The optical diffusivity of the PMMA film fabricated using this process is greater than that of normally fabricated film, demonstrating the feasibility of using this process to create newly designed optical diffusers.     

Photophysical properties of fluorescent PMMA/SiO2 nanohybrids for solar energy applications

This work concerning the photophysical properties of fluorescent nanohybrid films based on poly(methylmethacrylate) (PMMA) doped with coumarin dyestuff and entrapped with different concentrations of hydrophilic nanosilica. Spectroscopic tools were applied in order to determine the optimum concentration of nanosilica for the best optical properties for a matrix used as fluorescent solar concentrator. The optical constants and photoluminescence spectra of fluorescent nanohybrid films showed an enhancement of the photon trapping efficiency and matrix stability by increasing the concentration of SiO₂ nanoparticles.     

Synthesis and luminescent properties of PEO/lanthanide oxide nanoparticle hybrid films

In this study, we investigate the optical properties of lanthanide oxide nanoparticles dispersed in poly(ethylene oxide) (PEO) network as thermally stable polymeric films. The aim of this work is both to keep a good optical transparency in the visible domain and to obtain luminescent materials after incorporation of nanoparticles. For this purpose, we develop luminescent nanocrystals of oxides containing terbium ion as a doping element in Gd₂O₃. These sub-5-nm lanthanide oxides nanoparticles have been prepared by direct oxide precipitation in high-boiling polyalcohol solutions and characterized by luminescence spectroscopy. PEO/lanthanide oxide nanohybrid films are prepared by radical polymerization of poly(ethylene glycol) methacrylate after introduction of lanthanide oxide particles.As a first result; the obtained films present interesting luminescence properties with a very low lanthanide oxide content (up to 0.29 wt%). Furthermore, these films are still transparent and keep their original mechanical properties.Prior to describe the specific applications to optical use, we report here the dynamic mechanical analysis (DMA), X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), and luminescent properties of. nanohybrid films.     

Effect of laser treatment on the optical properties of poly(methyl methacrylate) thin films

In this work, the effect of laser pulse treatment on the optical properties of poly(methyl methacrylate) (PMMA) films has been studied experimentally. The second harmonic of a pulsed Nd:YAG laser at 532 nm and 6 ns pulse width with 10 Hz repetition rate was used to modify the surface of red-BS-dye-doped PMMA films. Samples were ablated with 50 and 100 laser pulses. Optical reflectance and transmittance spectra were obtained in the range of 200–2000 nm. The optical properties of the films were influenced by the pulse number significantly. The oscillator and dispersion energies of the films were determined using the Wemple-Didomenico model. The optical band gap energy was extracted using the Tauc method. Results show that the optical parameters of the films were changed significantly after laser treatment.     

Switching layer stability in a polymer bilayer by thickness variation

We use optical and scanning force microscopy to explore the possibility of switching the stability of a bilayer of poly(methyl methacrylate) (PMMA) on polystyrene by simply changing the film thickness. We show that for thin PMMA layers on thicker polystyrene films the PMMA layer is unstable to thickness fluctuations. However, polystyrene layers are unstable when they are substantially thinner than the now stable PMMA film. Dewetting morphologies are cataloged as a function of the thickness of individual polymer layers by identifying which layer is unstable by which mechanism, be it spinodal dewetting or heterogeneous thermal nucleation. Our results are in good agreement with a linear stability analysis of the influence of long-range dispersion forces, but also indicate the influence of film preparation and small variations of material properties.     

A novel approach for the preparation of PMMA-PDMS core-shell particles with PDMS in the shell

The core/shell particles consisting of polymethyl methacrylate (PMMA) core and polydimethylsiloxane (PDMS) shell via 3-(methacryloxypropyl)-trimethoxysilane (MPS) as the medium to link the core and shell were prepared in our present study by successive seeding polymerization under kinetically controlled conditions and were characterized by FT-IR, particle size analyzer, transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS).The picture of optical microscope showed the clear form of PDMS-0 and PDMS-40 (the content of PDMS in the particles), which approached to monodispersed distribution. Compared with the PMMA microspheres, PDMS-40 presented an evident core/shell structure through the observation of TEM. Additionally, the study of XPS revealed that PDMS could be grafted onto the surface of PMMA particles and the atomic ratio of C/Si on the surface of PDMS-40 was very close to the ratio of C/Si in the molecule of PDMS. The surface properties of the films produced from the core/shell microspheres also were investigated by contact angle method, contrast with the homopolymer of PMMA, the core/shell particles were more effective to form hydrophobic surface and the water repellency on the surface would be better than that of PMMA.     

The influence of UV-irradiation and support type on surface properties of poly(methyl methacrylate) thin films

Thin poly(methyl methacrylate) (PMMA) films were prepared by a solution casting on different supports (glass and aluminium plates with different gloss). UV-irradiation (λ = 254 nm) was used for polymer modification. Surface properties of PMMA were studied by contact angle measurements, attenuated total reflection infrared spectroscopy and optical microscopy. It was found that support type has no influence on surface properties of virgin PMMA, however, the changes in these properties were observed during UV modification of polymer film. The most efficient photochemical reactions appeared in sample placed on the rough Al, whereas the smallest effect was observed in polymer on the glass.     

The influence of γ-irradiation on some physical properties of chlorophyll/PMMA films

Films of poly(methylmethacrylate) PMMA doped with different concentrations of chlorophyll, from 2.5 up to 12.5 wt.%, have been prepared by casting method. Studies were carried out utilizing FT-IR, UV/vis, fluorescence, TGA and DC electrical conduction to characterize the structural, optical and thermal properties of the films before and after irradiation. Results revealed that the structural and chemical characterizations of PMMA films are affected by the addition of chlorophyll and increasing dose of γ-irradiation. FT-IR analysis revealed that the hydroxyl and carbonyl groups were responsible for the decrease of the bands intensities with increasing the dose rate up to 100 kGy. The change in these groups was attributed to competitive processes: decomposition with ester group abstraction and oxidation with formation of new oxidized carbonyls in the polymeric chains. The values of optical energy gap for the samples were decreased upon irradiation; this indicates that there is a charge transfer complexes arise between PMMA and chlorophyll. TGA analysis shows that the addition of chlorophyll to PMMA films enhances their thermal stability. The electric conduction data were interpreted on the basis of an intrachain one-dimensional interpolaron hopping model of Kuivalainen.     

Nonlinear optical switching and all-figures of merit in Bi2S3-xSex/PMMA nanocomposite films investigated by Z scan under visible CW laser

Bi2S3-xSex/poly(methyl methacrylate)(PMMA)nanocomposite films were prepared using microwave assisted synthesis with different compositions of x.Crystal structure,surface morphology,and optical properties were investigated to characterize the prepared nanocomposite films.The crystallinity and optical band gap of the prepared Bi2S3-xSex/PMMA were affected by x.The prepared samples showed a blue shift in the absorption edge.The laser power dependent nonlinear refraction and absorption of Bi2S3-xSex/PMMA nanocomposite films were investigated by using the Z-scan technique.The optical nonlinearity of the nanocomposite films exhibited switchover from negative nonlinear refraction to positive nonlinear refraction to negative nonlinear refraction effects,and from saturable absorption to reverse saturable absorption to saturable absorption with an increase and decrease in the composition.An interesting all-optical figure of merit was reported to assess the nanocomposite films for a practical device.It was calculated that the device all-figures of merit were based on the nonlinear response,which is important for the all-optical switching device.The results demonstrate that the optimized all-optical figures of merit can be achieved by adjusting the composition and input laser power,which can be used for the design of different all-photonic devices,and the results of nonlinear switching behavior can open new possibilities for using the nanocomposite films in laser Q-switching and mode-locking.     

Synthesis of transparent ZnO/PMMA nanocomposite films through free-radical copolymerization of asymmetric zinc methacrylate acetate and in-situ thermal decomposition

In this paper, a new and simple approach for in-situ preparation of transparent ZnO/poly(metyl methacrylate) (ZnO/PMMA) nanocomposite films was developed. Poly(methyl methacrylate)-co-poly(zinc methacrylate acetate) (PMMA-co-PZnMAAc) copolymer was synthesized via free-radical polymerization between methyl methacrylate (MMA) and zinc methacrylate acetate (ZnMAAc), where asymmetric ZnMAAc with only one terminal double bond (C=C) was applied to act as the precursor for ZnO nanocrystals and could avoid cross-link. Subsequently, transparent ZnO/PMMA nanocomposite films were obtained by in-situ thermal decomposition. Scanning electron microscope (SEM) image revealed that ZnO nanocrystals were homogeneously dispersed in PMMA matrix. With thermal decomposition time increasing, the absorption intensity in UV region and photoluminescence intensity of ZnO/PMMA nanocomposite films enhanced. However, the optical properties diminished when the thermal decomposition temperature increased. The TGA measurement displayed ZnO/PMMA nanocomposite films prepared by the in-situ synthesis method possessed better thermal stability compared with those prepared by the physical blending method and pristine PMMA films.     

Structure Formation of Blend and Sheath/Core Conjugated Fibers in High-Speed Spinning of PET,Including a Small Amount of PMMA

The blend of poly(ethylene terephthalate) (PET) and a small amount of polymer that has higher T _g than PET, such as polymethylmethacrylate (PMMA)—and is dispersed finely as immiscible particles in PET—exhibits lower molecular orientation than pure PET under high-speed fiber spinning. To obtain insight into the mechanism of the lower molecular orientation of the blend fiber, the sheath/core structure of PET (sheath)/PMMA (core) conjugated fiber (the same PET/PMMA weight ratio as in the blend fiber), was produced as a model. The thinning profile of the fiber diameter along the spinning line and the birefringence distribution of the cross-section were examined and compared among pure PET fiber, the conjugated fiber, and the blend fiber. The conjugated fiber had the lowest molecular orientation of PET in the sheath part, and its thinning process was accelerated similar to the blend fiber. As a result of the distribution of molecular orientation across the diameter of the conjugated fiber, it is considered that PMMA, having the high T _g , tends to solidify at a higher temperature (upstream) than PET in the thinning process, making the flow of PET accelerate as if it was pushed by PMMA. This causes the maximum dv/dx just before the solidification point to be smaller; therefore, the lower spinning stress, resulting in smaller birefringence of PET, can be considerable. This acceleration was generated at the interface of PET and PMMA, and spread toward the fiber surface as both polymers were thinning in elongational flow (in melt). On the other hand, close to the interface, molecules of PET were stretched by PMMA, resulting in an increase of birefringence. Such discussion is also considered to apply to the blend fiber. However, because the blend fiber had a significantly larger interface area compared with the conjugated fiber, it is considered that the increase of birefringence of PET by the interface drag force cannot be neglected. The larger particles of PMMA dispersed in PET results in the lower birefringence of PET that is supported by the elongation effect (i.e., the interface drag force).     

AFM, SEM and GIXRD studies of thin films of red polycarbazolyldiacetylenes

In this paper we report the results of a morphological and structural investigation on film properties of a soluble polydiacetylene, the poly[1,6-bis(3,6-dihexadecyl-N-carbazolyl)-2,4-hexadiyne] (polyDCHD-HS). The red films of this polymer, prepared by standard spin-coating techniques, revealed absence of linear dichroism and birefringence in contrast with the ordered mesophases detected by powder X-ray studies. In order to interpret the optical behavior of this polymer, we performed AFM and SEM studies of polyDCHD-HS films spun on hydrophylic and hydrophobic glass substrates. We found the presence of surfaces organized in rod-like particles, more regularly oriented on the hydrophylic substrate. GIXRD studies, carried out on films sufficiently thick to allow the observation of the diffraction pattern, reveled the presence of a lamellar structure with a spacing of 3.22 nm. The low intensity of the diffraction peaks and the isotropic linear optical properties of the films show that the lamellar mesophases are not extended over large areas. These findings were compared with the data obtained from AFM and SEM studies on films of two other polydiacetylenes, the poly[1-(3,6-dihexadexyl-N-carbazolyl)-6-(N-carbazolyl)-2,4-hexadyine] (polya-DCHD) and the poly[1,6-bis(3,6-dipalmitoyl-N-carbazolyl)-2,4-hexadyine] (polyDPCHD), spun on hydrophylic glass substrate. The results confirmed the presence of nodular morphologies which seem to be a general characteristic of this class of materials. The particles organization appears instead related to the chemical nature of the substituents on the carbazolyl rings.     

Cathodoluminescent and nonlinear optical properties of undoped and erbium doped nanostructured ZnO films deposited by spray pyrolysis

We have deposited zinc oxide (ZnO) and erbium doped zinc oxide (ZnO:Er) thin films on heated glass substrates using spray pyrolysis technique. The effect of erbium dopant on structural, morphological, luminescent and nonlinear optical properties was studied. The deposited films have been analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), ex situ compositional analysis (ESCA), profilometry, cathodoluminescence (CL) and third harmonic generation (THG) measurements. All films were polycrystalline, having a preferential growth orientation along the ZnO (0 0 2) plane, with a corresponding average crystallite size of less than 41 nm. Addition of erbium can effectively control the film surface morphology and its cathodoluminescent properties. The films containing low erbium concentration show a uniform surface covered with hexagonal shaped grains and a strong UV light emission intensity as well as TH response. In contrast, when the erbium doping ratio exceeds 3%, a porous surface with columnar textural growth becomes more pronounced, and a substantial reduction of the cathodoluminescent and TH response. A strong TH signal was obtained for the film with good crystalline quality at the concentration of 2%. Third order nonlinear optical susceptibility (χ^〈3〉) values of the studied materials were in the remarkable range of 10⁻¹² esu.     

The preparation of clay nanosheets-poly(ethylene terephthalate) hybrid materials

The preparation of hybrid materials of poly(ethylene terephthalate) (PET) with montmorillonite (Mont) clay was investigated using anchor monomers, i.e. hydroxyethyl isonicotinamide (HENA) or hydroxypentyltrimethylammonium iodide (HPTA), which both have cationic substituents to adsorb onto clay surfaces and a hydroxyethyl moiety (–CH₂CH₂OH) to react with the polymer chain terminal of PET. The condensation of the mixtures of the intercalation compounds, bis (2-hydroxyethyl) terephthalate (BHET) and HENA/Mont or HPTA/Mont, led to a homogenous and transparent PET hybrid in which the Mont clay particles were scattered homogenously. The HPTA/Mont hybrid films copolymerized with BHET exhibited a dramatic improvement in such characteristics as tensile strength and optical transparency.     

Synthesis and optical properties of basic fuchsin dye-doped PMMA polymeric films for laser applications: wide scale absorption band

Basic fuchsin dye-doped poly(methyl methacrylate) polymeric films were sensitized with various dye concentrations ranging from 0.0833 to 1.667 wt% of basic fuchsin. Their structure, linear absorption, and optical limiting properties were examined. The films were prepared using a simple and fast casting technique dissolved in chloroform for both the dye and the polymer. Structural characterizations were achieved by XRD, and the films showed an amorphous hump supporting the noncrystalline structure of studied polymeric composites. Spectrophotometer measurements were used to estimate the spectral absorption measurements of the films such as transmittance, absorbance with the calculations of absorption index (k), and optical energy band gap (E _g ) in the wavelength region from 190 to 2500 nm. Results show that the optical constants change with increasing the dye doping concentrations. It has been found that optical energy gap (E _g ) appearing that, both direct and indirect optical transitions are conceivable for these films. Optical limiting properties of the films with various dye concentrations were studied using a continuous wave He–Ne laser operating at 632.8 nm. The results appeared that the sample has an obvious optical limiting effect. The designed BF/PMMA composites can be applicable in wide-scale applications.     

Self-assembly between graphene sheets and cationic poly(methyl methacrylate) (PMMA) particles: preparation and characterization of PMMA/graphene composites

In this study, we presented a simple approach to prepare poly(methyl methacrylate) (PMMA)/graphene composites based on the self-assembly between graphene oxide (GO) sheets and cationic PMMA emulsion particles. Briefly, cationic PMMA emulsion particles were first synthesized by a soap-free emulsion polymerization process, in which methacryloyloxyethyl trimethyl ammonium chloride was used as the emulsifier, and then blended with the aqueous solution of GO. Through electrostatic attraction, the exfoliated GO sheets were tightly adhered on the PMMA particles. The GO sheets could be reduced in situ into graphene sheets by a chemical method, without the aggregation. The structure of the prepared composites and the influences of GO and graphene sheets on the properties of PMMA were investigated. Both GO and graphene sheets can increase the glass transition temperature and storage modulus of PMMA. Moreover, graphene sheets provided a more significant reinforcement effect.     

Microstructure and electro-optical properties of sol–gel derived Cd-doped ZnO films

The microstructure, and the electrical and optical properties of undoped zinc oxide (ZnO) and cadmium-doped ZnO (CZO) films deposited by a sol–gel method have been investigated. The films have a polycrystalline structure with hexagonal wurtzite ZnO. Scanning electron microscopy (SEM) images indicated that the films have a wrinkle network with uniform size distributions. The elemental analyses of the CZO films were carried out by energy dispersive X-ray analysis. The fundamental absorption edge changed with doping. The optical band gap of the films decreased with Cd dopant. The optical constants of the films such as refractive index, extinction coefficient and dielectric constants changed with Cd dopant. A two-probe method was used to investigate the electrical properties, and the effect of Cd content on the electrical properties was investigated. The electrical conductivity of the films was improved by incorporation of Cd in the ZnO film.     

The influence of the quantum dot/polymethylmethacrylate composite preparation method on the stability of its optical properties under laser radiation

Photoluminescent semiconductor nanocrystals, quantum dots (QDs), are nowadays one of the most promising materials for developing a new generation of fluorescent labels, new types of light-emitting devices and displays, flexible electronic components, and solar panels. In many areas the use of QDs is associated with an intense optical excitation, which, in the case of a prolonged exposure, often leads to changes in their optical characteristics. In the present work we examined how the method of preparation of quantum dot/polymethylmethacrylate (QD/PMMA) composite influenced the stability of the optical properties of QD inside the polymer matrix under irradiation by different laser harmonics in the UV (355 nm) and visible (532 nm) spectral regions. The composites were synthesized by spin-coating and radical polymerization methods. Experiments with the samples obtained by spin-coating showed that the properties of the QD/PMMA films remain almost constant at values of the radiation dose below ~10 fJ per particle. Irradiating the composites prepared by the radical polymerization method, we observed a monotonic increase in the luminescence quantum yield (QY) accompanied by an increase in the luminescence decay time regardless of the wavelength of the incident radiation. We assume that the observed difference in the optical properties of the samples under exposure to laser radiation is associated with the processes occurring during radical polymerization, in particular, with charge transfer from the radical particles inside QDs. The results of this study are important for understanding photophysical properties of composites on the basis of QDs, as well as for selection of the type of polymer and the composite synthesis method with quantum dots that would allow one to avoid the degradation of their luminescence.     

SnO$lt;sub$gt;2$lt;/sub$gt;纳米晶体的制备、结构与发光性质

使用软化学方法在碱性溶液中制备出了颗粒尺寸分布均匀的SnO₂纳米颗粒,使用透射电子显微镜（TEM）、X射线衍射（XRD）、光致发光谱（PL）和光吸收谱等方法分析与表征了SnO₂纳米颗粒的结构和光学性能.实验中通过表面活性剂的加入来控制纳米颗粒的结晶与凝聚.XRD,TEM的结果表明,原始制备出的SnO₂纳米颗粒的平均粒径小于4 nm,为完好的晶体状态.纳米颗粒经过400—1000 ℃退火后晶粒尺寸进一步增大.光吸收谱表明,相对于体材料,纳米颗粒的禁带宽度展宽并随颗粒尺寸增大而红移.光致发光谱测试表明,不同温度下退火的SnO₂纳米颗粒在350—750 nm有较强的发光,研究表明这是来源于颗粒表面的氧空位缺陷发光. 关键词： 氧化锡 表面活性剂 纳米颗粒 光致发光     

Investigation of third-order nonlinear optical properties of NNDC-doped PMMA thin films by Z-scan technique

A novel chalcone derivative, (2E)-1-(2,4-di- chloro-5-fluorophenyl)-3-[4-dimethylamino)phenyl]prop-2-en-1-one, abbreviated as NNDC, was prepared and characterized by elemental analyses, infrared (IR) and proton nuclear magnetic resonance (¹H NMR) spectrum, and thermal analyses. The NNDC-doped poly(methyl methacrylate) (PMMA) thin films with five different doping concentrations by weight were prepared by using a spin-coating method. Their linear optical properties were investigated by using a prism coupling measuring system. The third-order nonlinear optical properties of NNDC in 1,2-dichloroethane (NNDC/1,2-dichloroethane) solution and NNDC-doped PMMA (NNDC/PMMA) films were investigated by using the laser Z-scan technique with 20 ps pulses at 532 nm. A self-focusing effect was observed from the Z-scan curves for solution and thin films and the nonlinear refractive index of the film increases with the increase of the doping concentration. In addition, nonlinear absorption was negligible for all samples. The magnitude of third-order nonlinear refraction index n ₂ and the third-order nonlinear susceptibility χ ⁽³⁾ for thin films were 10⁻¹⁵ m²/W and 10⁻⁹ esu, respectively, which are about three orders larger than that of NNDC/1,2-dichloroethane solution. Some necessary analyses were presented. The results show that this material is a promising candidate for application in the nonlinear optical devices at 532 nm.