Optical and two‐photon absorption analysis of radiation‐grafted fluoropolymer

Grafting by gamma irradiation has a significant influence on the dispersion properties of polymeric materials. Accordingly, we study the effect of grafting on the material electronic structure parameters such as the fundamental absorption edge and bandgap structure. The optical absorption of grafted polymeric films of poly(tetrafluoroethylene‐co‐perfluorovinyl ether) (PFA‐g‐PAAc) is determined in a very wide spectral range of 0.2–3 μm. The nonlinear two‐photon absorption coefficient is determined that showed an increase as a result to the grafting process. Moreover, a significant increase in the optical conductivity for the polymeric films is acquired after grafting. Positron annihilation spectroscopy is used to study polymer structure and volume size of nanoholes of Ps. The data revealed an increase of crosslinking with a smaller average volume size with grafting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2045–2051, 2010     

Correlation of physico-chemical,mechanical and electrical properties of ultraviolet-degraded poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) films have been exposed to ultraviolet radiation. Changes in physico-chemical, mechanical and electrical properties which occur in the films were examined. It was found that the specific viscosity, tensile strength, elongation at break, relative dielectric constant and dielectric strength decrease, while the dielectric loss factor, density, optical density of the ir spectrum band which refers to the trans form of the PET molecule, as well as the quantity of carboxylic end groups, increase.Least squares analysis and function straightening methods were used for the interpretation of the experimental data. Correlating relationships between measured parameters were established using the same methods.Special attention was paid to the changes in the electrical properties of poly(ethylene terephthalate), because no data are available so far. Mathematical correlations with chemical and mechanical properties were established.     

Optical characterization of pristine poly(3‐hexyl thiophene) films

We describe a comprehensive model for the optical properties of pristine films of poly‐(3‐hexylthiophene) (P3HT). The presented model is anisotropic with the optical axis normal to the substrate plane, which is consistent with previous x‐ray diffraction studies that show preferential edge‐on packing of the polymer chains on the substrate. Peak locations and spacings are defined using a Huang‐Rhys vibronic progression consistent with known phonon energies. We demonstrate that the model fits variable‐angle spectroscopic ellipsometry and normal‐incidence transmission data well, and accurately predicts angle‐ and polarization‐dependent transmission and reflection data. The spectral features of the optical constants used in the model are in excellent agreement with published spectroscopic data on P3HT. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Resonant soft x‐ray scattering and reflectivity study of the phase‐separated structure of thin poly(styrene‐b‐methyl methacrylate) films

Combined soft X‐ray scattering and reflectometry techniques promise analysis of polymer thin film domain structure and composition without resorting to chemical modification or isotopic labeling. This work explores the capabilities of these techniques in polymer films of poly(styrene‐b‐methyl methacrylate) (P(S‐b‐MMA)). The results demonstrate that the techniques give detailed information on the domain structure of thin films using well‐known modeling procedures. Discrepancies were noted between the X‐ray optical parameters that are needed to best fit the reflectivity data to the model and the expected parameters. The sources of these discrepancies are discussed in terms of instrument configuration parameters, sample attributes, and, particularly, anisotropy of the chromophore parameters. The results show that fitting the soft X‐ray reflectivity data is much more sensitive to these X‐ray optical parameters than the soft X‐ray scattering data. Nevertheless, fits to both types of data yield quantitative measures of the polymer film's lamellar morphology that are consistent with each other and with literature values. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Absolute absorption measurements of polymer films for optical waveguide applications by photothermal deflection spectroscopy

A self‐contained experimental technique is proposed for measuring the absolute optical absorption spectra, thermal diffusivity, and thermal conductivity of polymer thin films. The technique is based on photothermal deflection spectroscopy and provides sensitivity that is high enough to quantify the very small optical absorption losses in polymer films used for optical waveguide applications. The capabilities of the technique are demonstrated with measurements performed on thin films of poly(methyl methacrylate) and a fluorinated polymer (CYTOP). An error analysis is presented, and the factors are discussed that influence the accuracy of the technique. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2717–2726, 2001     

Correlation of Molecular Assembly and Interactions in Crystals and Langmuir–Blodgett Films of N‐(2,4‐dinitrophenyl)‐n‐octadecylamine

Correlation of molecular organization in crystals and in ultrathin films is of fundamental interest in the design of molecular materials based on thin films. We have chosen as a test case, N‐(2,4‐dinitrophenyl)‐n‐octadecylamine (DNPOA), a potential candidate for the fabrication of Langmuir–Blodgett (LB) films for quadratic nonlinear optical applications. Like several other 4‐nitroaniline derivatives, DNPOA does not form stable monolayers at the air–water interface. This has precluded investigations of their organization in LB films. We have stabilized composite Langmuir films of DNPOA with the phospholipid molecule DSPC and fabricated their LB films. Successful growth of single crystals of DNPOA allowed structure determination and detailed analysis of molecular associations in the solid state. Electronic absorption spectra of DNPOA in solution, in the solid state and in the LB film are investigated. Modeling of the various spectral signatures by semiempirical computations on molecular clusters extracted from the crystal lattice provides insight into the correlation between the molecular organization in crystals and in LB films.     

Novel electrochemical synthesis and characterisation of poly(methyl vinylsilane) and its co-polymers

The electrochemical synthesis and characterisation of poly(methyl vinylsilane) and a series of poly(methyl vinylsilane-co-metallocenes) network polymers are described in detail. This class of polymers are not accessible through Wurtz coupling reaction and are however prepared by electro-reduction of dichloro methyl vinylsilane in a non-aqueous system using aluminum electrodes in a single compartment cell. These polymers have been characterised using UV, FTIR, XRD, SEM and NMR spectral techniques. Cyclic voltammetric studies of the above polymers reveal their conducting behavior. These polymers show optical properties as explained from the results. Polymers of this type are proposed as potential soluble precursors for SiC and metal doped SiC materials.     

Spectroscopic Ellipsometry for Characterization of Thin Films of Polymer Blends

Morphology, composition, miscibility, interdiffusion, and interactions at interfaces are important quantities of polymer blends. Many of these parameters can be probed with spectroscopic ellipsometry. Ellipsometry in the visible spectral range is very suitable for determination of thicknesses and the high frequency refractive indices of thin organic films. However the spectral contrast is low for many polymers in comparison to infrared spectroscopic ellipsometry (IRSE) where specific contributions of the molecular vibrations are probed. In the presented study the infrared optical constants of a double layer (206.6 nm in total) of poly(n-butyl methacrylate) (PnBMA) and poly(vinyl chloride) (PVC) and of the films of the single compounds have been determined with optical simulations using layer models. The multiple layer model served for simulation of the ellipsometric spectra taken after an annealing induced mixing process in a polymeric double layer. The ellipsometric spectra of a not completely mixed sample could be fitted in a three-layer model, in which a mixed interphase in between the two layers of the polymers is formed due to interdiffusion.     

Generalization of multivariate optical computations as a method for improving the speed and precision of spectroscopic analyses

Multivariate optical computations (MOCs) offer improved analytical precision and increased speed of analysis via synchronous data collection and numerical computation with scanning spectroscopic systems. The improved precision originates in the redistribution of integration time from spurious channels to informative channels in an optimal manner for increasing the signal‐to‐noise ratio with multivariate analysis under the constraint of constant total analysis time. In this work, MOCs perform the multiplication and addition steps of spectral processing by adjusting the integration parameters of the optical detector or adjusting the scanning profile of the tunable optical filter. Improvement in the precision of analysis is achieved via the implicit optimization of the analytically useful signal‐to‐noise ratio. The speed improvements are realized through simpler data post‐processing, which reduces the computation time required after data collection. Alternatively, the analysis time may be significantly truncated while still seeing an improvement in the precision of analysis, relative to competing methods. Surface plasmon resonance (SPR) spectroscopic sensors and visible reflectance spectroscopic imaging were used as test beds for assessing the performance of MOCs. MOCs were shown to reduce the standard deviation of prediction by 15% compared to digital data collection and analysis with the SPR and up to 45% for the imaging applications. Similarly, a 30% decrease in the total analysis time was realized while still seeing precision improvements. Copyright © 2008 John Wiley & Sons, Ltd.     

Evaluation of Poly(o‐phenylenediamine) Films for Application as Insulating Layers upon Carbon Substrates for Use within Sonochemically Fabricated Microelectrode Arrays

The formation of insulating layers of poly(o‐phenylenediamine) via electropolymerization was performed on single carbon screen‐printed electrodes. The effects of experimental parameters on the properties of the film were investigated, allowing for technique optimization. These conditions were then used to deposit films upon surfaces of 100 interconnected electrodes, with cyclic voltammetry used to study the electroactivity of the resulting electrodes. The insulating property of the film, for use in the formation of microelectrode array amperometric sensors, was evaluated. Finally, the insulated sensors were exposed to ultrasonic ablation to form microelectrode arrays, and these were subsequently assessed using optical and electrochemical techniques.     

Homogeneous poly(L‐lactic acid)/chitosan blended films

This work reports an optimized and simple methodology for the preparation of poly(L‐lactic) acid/chitosan (CHT) blends by solvent casting based on the use of a common solvent: hexafluor‐2‐propanol. Films with different component fractions were successfully prepared and did not show visible phase separation. Such biodegradable films have potential to be used in distinct biomedical and environmental applications. The composition effect on film wettability and morphology was investigated by contact angle measurements and scanning electron microscopy. Swelling measurements were also conducted. The composition effect on their thermal properties was analyzed by differential scanning calorimetry. It was found that crystallization is almost suppressed for CHT fractions above 50%. The film miscibility as a function of their composition was evaluated by optical microscopy and Fourier transform infrared spectroscopy imaging. These results evidenced the good miscibility at the microscopic level of the blends. The viscoelastic behavior of the developed films was also studied for the first time by dynamical mechanical analysis (DMA) in an unconventional way: their mechanical properties were measured while they were immersed in gradient compositions of water/ethanol mixtures. This allowed to analyze the glass transition dynamics of the CHT fraction, which would not be possible with conventional DMA tests. DMA temperature scans were also conducted. Copyright © 2014 John Wiley & Sons, Ltd.     

Structural and optical characterization of thermally evaporated cadmium sulfide thin films

The article reports the structural and optical properties of vacuum‐evaporated cadmium sulfide (CdS) films with different thicknesses at room temperature. The structural investigations performed by means of X‐ray diffraction (XRD) technique have showed that all the films have the zinc‐blende structure, a face‐centered cubic form with lattice constants a = b = c = 5.82 Å and point group F4 3m. Crystallite sizes calculated from Scherrer relation are in the range of 173–345 Å. So far, because the optical parameters of the metastable cubic CdS have not been so well known, we apply spectroscopic ellipsometry to determine the thickness, optical constants and energy band gap of CdS thin film deposited by thermal evaporation onto opaque gold substrate, a perfect reflectivity and inert metal. As shown the measured spectral behavior of the optical constants and the band gap value of CdS thin film are in agreement with those obtained by the reflectance and transmittance methods. The energy band gap of CdS thin film determined from the spectral behavior of the absorption coefficient is about 2.46 eV. Copyright © 2008 John Wiley & Sons, Ltd.     

Facile syntheses,morphologies, and optical absorptions of P3HT coil‐rod‐coil triblock copolymers

Here we report syntheses, photophysical properties, and morphologies of a series of coil‐rod‐coil ABA triblock copolymers containing highly regioregular poly(3‐hexylthiophene) (P3HT) as the central rod block. A new methodology, based on the coupling reaction between living polymeric anions [polystyrene, polyisoprene, and poly(methyl methacrylate)] and aldehyde terminated P3HT, was successfully developed to synthesize the triblock copolymers with low polydispersities. This coupling reaction was effective for building blocks with a variety of molecular weights; therefore, a good variation in compositions of the triblock copolymers could be feasibly achieved. The non‐P3HT coil segments and the solvents were found to exhibit noticeable effects on morphologies of the spin‐coated thin films. Attachment of the coil segments to P3HT did not change the optical absorption of the P3HT segment as the block copolymers were dissolved in solution regardless the chemical structure and the molecular weight of the coil segment. Interestingly, different UV–vis absorption behaviors were observed for the spin‐coated thin films of the block copolymers, which closely related to their morphologies. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3311–3322, 2010     

Spectroelectrochemical Sensing Based on Multimode Selectivity Simultaneously Achievable in a Single Device. 19. Preparation and Characterization of Films of Quaternized Poly(4‐vinylpyridine)‐silica

Quaternized poly(4‐vinylpyridine) (QPVP) has been incorporated as an anion exchanger into sol‐gel derived silica films for use in a spectroelectrochemical sensor. The preparation, characteristics and performance of these films are described. The films, which are spin‐coated onto the surface of a planar optically transparent electrode, are optically transparent and uniform. Scanning electron microscopy and spectroscopic ellipsometry have been used to examine film structure, thickness and optical properties. These films have been shown both spectroscopically and electrochemically to preconcentrate ferrocyanide, a model analyte for the sensor. The films can be regenerated for multiple measurements by exposure to 1 M KNO₃. The effects of polymer molecular weight and storage conditions on film performance are described. The overall response of this film is comparable to the poly(dimethyldiallylammonium chloride)‐silica films previously used for this sensor.     

UV‐photodimerization in uracil‐substituted dendrimers for high density data storage

Two series of uracil‐functionalized dendritic macromolecules based on poly (amidoamine) PAMAM and 2,2‐bis(hydroxymethylpropionic acid) bis‐MPA backbones were prepared and their photoinduced (2π+2π) cycloaddition reactions upon exposure to UV light at 257 nm examined. Dendrimers up to 4th generation were synthesized and investigated as potential materials for high capacity optical data storage with their dimerization efficiency compared to uracil as a reference compound. This allows the impact of increasing the generation number of the dendrimers, both the number of chromophores, as well as the different steric environments, on the performance of each series of dendrimers to be investigated. The (uracil)₁₂‐[G‐2]‐bis‐MPA and (uracil)₈‐[G‐1]‐PAMAM were observed to have high dimerization efficiency in solution with different behavior being observed for the PAMAM and bis‐MPA dendrimers. The dendrimers with the best dimerization efficiency in solution were then examined in the solid state as thin films cast on quartz plates, and their film qualities along with their photodimerization performance studied. High quality films with a transmission response of up to 70% in 55 s. when irradiated at 257 nm with an intensity of 70 mW/cm² could be obtained suggesting future use as recording media for optical data storage. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4401–4412, 2007     

Effect of trifluoromethyl substituents on birefringence of polystyrene

Transparent thermoplastic polymers that exhibit no birefringence are ideal for optical components such as optical films for liquid crystal displays and various lenses. Copolymerization of a positive birefringent monomer with a negative monomer is an effective technique for obtaining low birefringent polymers, especially zero‐photoelastic birefringence polymers that exhibit no photoelastic birefringence even during elastic deformation. We prepared four types of trifluoromethyl‐substituted polystyrenes. By substituting hydrogens at the ortho or meta positions of the benzene ring of polystyrene, we demonstrated that poly(2‐(trifluoromethyl)styrene), poly(3‐(trifluoromethyl)styrene), and poly(3,5‐bis(trifluoromethyl)styrene) had negative photoelastic coefficients. However, poly(4‐(trifluoromethyl)styrene) had a positive photoelastic coefficient similar to that of polystyrene. Based on these results, we synthesized a zero‐photoelastic birefringence polymer of poly(2‐(trifluoromethyl)styrene‐co‐4‐(trifluoromethyl)styrene) (55/45 wt.) exhibiting no photoelastic birefringence in elastic deformation, in which the positive photoelastic birefringence of the poly(4‐(trifluoromethyl)styrene) unit was compensated for by the negative photoelastic birefringence of the poly(2‐(trifluoromethyl)styrene) unit. The discovery of polymers having negative photoelastic coefficients is valuable for the design and synthesis of zero‐photoelastic birefringence polymers. The four types of trifluoromethyl‐substituted polystyrenes are promising optical materials because they have high transparency (transmittance > 89–92% for 27–34‐µm thickness films) in the visible and near‐infrared regions and a high decomposition temperature of approximately 400°C. Copyright © 2016 John Wiley & Sons, Ltd.     

UV‐induced refractive index modulation of photoreactive polymers bearing N‐acylcarbazole groups

In this study, we report on the synthesis and characterization of photoreactive polymers bearing N‐acetylcarbazole and N‐formylcarbazole groups, respectively. These polymers were easily accessible by polymer analogous acylation of commercially available poly‐(2‐vinylcarbazole). While poly(1‐(2‐vinyl‐9H‐carbazol‐9‐yl)ethanone) (poly‐ 1 ) undergoes a partial photochemical Fries rearrangement, poly(2‐vinyl‐9H‐carbazole‐9‐carbaldehyde) (poly‐ 2 ) decarbonylates smoothly when exposed to UV irradiation. The difference in reactivity between the two acylated polymers is because of the lower stability of the formyl radical, which is formed in the first stage of this photoreaction. Ellipsometric measurements of thin films showed that the photo‐Fries rearrangement in poly‐ 1 causes a change in refractive index by Δn = +0.01 at 650 nm. UV illumination of poly‐ 2 results in a change of the refractive index by Δn = +0.03 at 650 nm, which can be explained by the high yield of the photodecarbonylation of the N‐formylcarbazole groups. Refractive index patterns can be easily realized using lithographic techniques as demonstrated by optical microscopy using a phase contrast set‐up for visualization. Patterned films of poly‐ 1 and poly‐ 2 with feature sizes of about 5 μm were obtained with a mask aligner. Photoreactive polymers bearing N‐acylcarbazole groups are of potential interest for optical applications such as waveguides, optical switches, and data storage devices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Vacuum ultraviolet optical analysis of spin‐cast chitosan films modified by succinic anhydride and glycidyl phenyl ether

Optical properties of spin‐cast chitosan films were determined in the vacuum ultraviolet (VUV) through visible regions of the spectrum using spectroscopic ellipsometry. The onset of absorption in the ultraviolet was determined for chitosan films modified with succinic anhydride (SA) and glycidyl phenyl ether (GPE). This absorption was accounted for by including Gaussian and Tauc–Lorentz shaped oscillators in the optical model. VUV through visible optical constants were determined for these modified films, as well as for immunoglobulin G (IgG) attached to GPE‐modified samples. Several resonant oscillator structures exhibit greatly differing oscillator parameters for the as‐deposited, as well as SA‐ and GPE‐modified films. These in‐plane and out‐of‐plane oscillator strengths, energy positions, and broadening were determined and tabulated, and their chemical origins identified. A phenyl resonant π‐bond at approximately 6.3 eV was observed for the GPE‐modified sample. This was not present in the bare chitosan data. GPE contains a phenyl group in the molecule and absorption due to it is clearly identified. Clarity of data after surface chemical modification is due to the high surface sensitivity of VUV ellipsometry. Copyright © 2007 John Wiley & Sons, Ltd.     

A numerical study of expected accuracy and precision in Calibration-Free Laser-Induced Breakdown Spectroscopy in the assumption of ideal analytical plasma

Calibration-Free Laser-Induced Breakdown Spectroscopy (CF-LIBS) has been proposed several years ago as an approach for quantitative analysis of Laser-Induced Breakdown Spectroscopy spectra. Recently developed refinement of the spectral processing method is described in the present work. Accurate quantitative results have been demonstrated for several metallic alloys. However, the degree of accuracy that can be achieved with Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of generic samples still needs to be thoroughly investigated. The authors have undertaken a systematic study of errors and biasing factors affecting the calculation in the Calibration-Free Laser-Induced Breakdown Spectroscopy spectra processing. These factors may be classified in three main groups: 1) experimental aberrations (intensity fluctuations and inaccuracy in the correction for spectral efficiency of a detection system), 2) inaccuracy in theoretical parameters used for calculations (Stark broadening coefficients and partition functions) and 3) plasma non-ideality (departure from thermal equilibrium, spatial and temporal inhomogeneities, optical thickness, etc.). In this study, the effects of experimental aberrations and accuracy of spectral data were investigated, assuming that the analytical plasma is ideal. Departure of the plasma conditions from ideality will be the object of future work. The current study was based on numerical simulation. Two kinds of metallic alloys, iron-based and aluminum-based, were studied. The relative weight of the error contributions was found to depend on the sample composition. For the here-investigated samples, the experimental aberrations contribute to the overall uncertainty on the quantitative results more than theoretical parameters. The described simulation method can be applied to the Calibration-Free Laser-Induced Breakdown Spectroscopy analysis of any other kind of sample.     

Quantitative SIMS analysis of SiC

We performed a systematic study of ion‐implanted 6H‐SiC standards to find the optimal regimes for SIMS analysis. Relative sensitivity factors (RSFs) were acquired for operating conditions typical of practical SIMS applications. The experimental SiC RSFs were compared with those found for silicon: 1 the matrix effect was insignificant in most cases. It was found that the SiO^? cluster ion cannot represent correctly the real oxygen distribution in SiC. The physics of the effect is discussed. Copyright © 2003 John Wiley & Sons, Ltd.