Multilayer method as a tool for depth dependent polymer film photodegradation studies

A new polymer film destructive depth profiling protocol is presented for the analysis of photo‐ and thermally degraded thin films on the depth scale of less than 100 microns. The method, demonstrated here on thin films of poly(vinyl chloride) (PVC), provides a means of preparation of thin laminates of high optical quality comprised of many (>20) thin layers of individual thickness less than 15 microns. The constituent layers are fused together under appropriate pressure, temperature and time treatment to yield a film assembly of high optical quality that behaves like a uniform single layer during photodegradation exposure, but which may still be separated after treatment. Compared to previous techniques, this new method is relatively simple and non‐labor intensive. Film adhesive properties are controlled to within ± 5% Concentration depth profiles of polymer photolysis products were reconstructed by analyzing each of the separated layers using UV‐visible spectrophotometry. The continuity of these film assemblies with respect to mechanical properties, adhesive properties and the depth distribution of key photolysis reagents and products was confirmed using photothermal and reference microscopy techniques. Optical absorption depth profiles examined in UV‐ photodegraded poly(vinyl chloride) (PVC) films exhibited the classic dependencies expected in the presence of nitrogen and oxygen atmospheres.     

Improved environmental stability in poly(p-phenylene vinylene)/layered silicate nanocomposite

Polymer-rich/clay-rich phase-separated, polymer-layered silicate nanocomposites are prepared through a solution blending of poly(xylylidene tetrahydrothiophenium chloride) with two kinds of layered silicates. By spin-coating, thin films of each phase were obtained, followed by thermal elimination of tetrahydrothiophene and HCl to final poly(p-phenylenevinylene) (PPV)/layered silicate nanocomposite. At ambient conditions, the PPV films are easily photodegraded due to the oxygen diffused in. Poly(p-phenylenevinylene)/layered silicate nanocomposite showed improved environmental stability against photodegradation under an air ambient condition. Additionally, optical absorption and photoluminescence measurements demonstrate that the thin films of clay-rich phase are much less photodegraded than those of polymer-rich and PPV reference.     

Photoacoustic spectroscopy and thermal diffusivity measurement on hydrogenated amorphous carbon thin films deposited by plasma-enhanced chemical vapor deposition

In this work, the photoacoustic spectroscopy and the open photoacoustic cell method are employed in the thermo-optical characterization of hydrogenated amorphous carbon thin films. The samples were fabricated in a modified plasma-enhanced chemical vapor deposition system with varying deposition time from 2 to 30 min. The optical absorption spectrum was determined for wavelengths of 300 to 2200 nm. The optical transmission spectrum was also recorded from photoacoustic spectroscopy. The energy gap was determined from the optical absorption spectra. The thermal diffusivity was found using open photoacoustic cell technique. The thickness of the films was confirmed to be an important parameter for the optimization of the fabrication process and the improvement of thermo-optical performances of the thin films. Spectroscopic results showed lower absorption and UV transparency for the thinner film. In the infrared region the − OH band decreased with increasing film thickness. On the other hand, the thermal diffusivity measurement presented an increase of this variable with decreasing film thickness.     

Electrical and optical properties of polymer‐Au nanocomposite films synthesized by magnetron cosputtering

Polymer‐Au nanocomposite films were prepared by co‐sputtering from two independent magnetron sources. By sputtering from gold and polytetrafluoroethylene (PTFE) magnetrons, we prepared homogenous composite films using a rotatable sample holder. The microstructure of the nanocomposites was studied by transmission electron microscopy (TEM). The resistivity drops from 10⁷ to 10^?3 Ohm cm over a narrow range of metal content. The thin composite films show a strong optical absorption in the visible region due to surface plasmon resonances. The optical absorption has a strong dependence on the metal content, showing a red shift of the absorption peak from 550 nm to more than 700 nm with increasing gold content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Vergleich von thermisch und photolytisch ausgelöstem Abbau von PVC-Preßlingen und -Folien

Comparative investigations of PVC discs and foils concerning their thermal and photolytical behaviour showed an expiration of thermal degradation in the mass, whilst the photo processes injure only the surface of a sample. The investigations of polymer samples with different masses have demonstrated a constant rate of thermal dehydrochlorination in nitrogen, which was not influenced by the polymer mass. The degradation experiments in air resulted in an increased HCl-elimination with increasing degradation time. Oxidation reactions which occur in the presence of air cause an accelerated degradation and therefore the dehydrochlorination reaction is appointed as an additional reaction and not in competition with the HCl-elimination process. The influence of UV-light on PVC-discs and foils efforted a much higher dehydrochlorination rate; the energy of the rays is able to stimulate all types of chlorine atoms at the surface. The photolytical injury of the surface increased with degradation time resulting in a decrease of the degradation rate. The degraded and cross-linked material is insoluble in all solvents.     

Impact on nonlinear/linear optical and structural parameters in quaternary In15Ag10S15Se60 thin films upon annealing at different temperatures

In the present study, the effect of thermal annealing on structural, linear, and nonlinear optical properties of quaternary chalcogenide In₁₅Ag₁₀S₁₅Se₆₀ thin film has been reported. The bulk sample synthesized by the melt quenching technique was used for the thin film preparation by the thermal evaporation method. Post deposition, the thin films were annealed at different temperatures like 100 °C, 150 °C, 200 °C, and 250 °C for 2 hs. X-ray diffraction (XRD) and Raman spectroscopy were used for structural studies, which showed the increase in crystalline phases with the increase of annealing temperature. The morphological images taken by field emission scanning electron microscope (FESEM) showed the densification and enlargement of scattered grains for annealed films. Furthermore, the constituent elements and their percentage in the sample were confirmed by Energy dispersive X-ray analysis (EDX). The linear and nonlinear optical parameters were calculated from the transmittance data obtained from UV–Vis spectroscopy in the wavelength range of 600–1100 nm. There is a large reduction in third-order nonlinear susceptibility at the higher annealing temperature. Subsequently, the transmission increased, whereas the absorption decreased with the annealing temperature. The extinction coefficient decreased while there was an increase in optical bandgap for the annealed films due to the decrease in surface defects and disorder, which forms the localized states in the bandgap. The oscillator energy, dispersion energy, dielectric constant, optical conductivity were calculated and discussed in detail. The change in both linear and nonlinear parameters by thermal annealing could be useful for controlling the optical properties of In₁₅Ag₁₀S₁₅Se₆₀ thin film, which could be the preferable candidate for numerous photonic applications.     

Spatial depth profiling of chromophores in thin polymer films using photopyroelectric spectroscopy

Frequency domain photopyroelectric effect spectrometry (FD-PPES) is a recent spectroscopic technique that may be used to recover depth profiles of optical absorption in thin films on a noncontact and nondestructive basis. In this work a series of well characterized thermally homogeneous samples were prepared that exhibited continuous or discrete subsurface profiles of optical absorption. Multifrequency FD-PPES measurements made on these samples were compared to theory using a heat transfer model, which we have developed for a multilayer thermally homogeneous absorber. Excellent agreement between experiment and theory was obtained for these model studies. While both phase and magnitude channels of the FD-PPES response give depth profiling information, the phase response is especially sensitive to variations in the subsurface profile of optical absorption. By means of the phase response it is possible to determine the number and spatial positions of absorbers in a series of discrete absorbing layers. The FD-PPES. technique has excellent potential for analysis and nondestructive evaluation of polymer films.     

Studies of the solid-state thermal degradation of PVC. I. Autocatalysis by hydrogen chloride

The thermal degradation of virgin and HCI-treated PVC in powder form, as well as of PVC films of different thicknesses, has been studied as a function of time and temperature. The rate of dehydrochlorination was determined conductimetrically and from the polyene sequence distributions as obtained by UV spectroscopy. Increases in the rate of dehydrochlorination, ranging between 30 and 45%, were observed at all temperatures for the samples pretreated with HCI, while the corresponding activation energies were found to be lower by about 20%. For the PVC films, the rate increased with thickness, i.e., with longer residence time of evolved HCI within the sample. The results offer insight regarding the autocatalytic role of evolved HCI.     

Studies on photodegradation of poly(vinyl chloride), part 3

PVC films were degraded by outdoor exposure, irradiation by a weatherometer and heating by an electric oven. In PVC films subjected to outdoor exposure and to irradiation by the weatherometer at a low temperature, e. g. sample surface temperature of 0°C, photo-oxidation and scission of the main chain were caused, but dehydrochlorination or formation of solvent-insoluble substances were not observed. In contrast, PVC subjected to irradiation by the weatherometer at a high temperature, e. g. sample surface temperature of 80°C, showed a degradation tendency similar to that of PVC heated at 200°C in the electric oven, and decomposition of the thermal degradation type characterized by dehydrochlorination, formation of polyenes and formation of solvent-insoluble substances were observed.     

Effect of thermal decomposition on dielectric relaxation process of poly(vinyl chloride)

Dielectric absorption caused by the molecular relaxation of thermally decomposed poly(vinyl chloride) in air was studied on samples in the form of thin films. It was found that, with the progress of thermal decomposition, the magnitude of α dielectric absorption changes in three stages: (1) initial decrease in magnitude corresponding to the process of the formation of polyene sequences caused by dehydrochlorination; (2) ensuing increase corresponding to the deformation of polyene sequences attributed to oxidation; (3) final decrease corresponding to the formation of crosslinks.     

Photothermal methods for the measurement of thermal properties of thin polymer films

The absorption of radiation in a sample gives rise to local heating. With a suitable modulated or pulsed source of radiation, a spatially well defined instantaneous heat source can be readily implemented. Radiation induced thermal transients are, therefore, the ideal heat sources for studies of thermal processes in thin films. Application of this method for measurements of thermal diffusivity and temperature dependent properties of thin polymer films are discussed. Imaging of inhomogeneities and depth profiling are another important area of application for these techniques. A number of applications emphasizing the various photoacoustic and photothermal techniques, their advantages and drawbacks are covered in detail.     

Impacts of thickness reduction and heat treatment on the optical properties of thin chalcogenide films

Bi-based chalcogenides, in the form of thin crystalline films, were deposited at different thicknesses onto highly cleaned glass slides with the aid of vacuum thermal evaporation technique. The influence of thermal annealing on the optical properties of Bi₂Te₃-Bi₂Se₃ films at different thicknesses is investigated in this work. Wavelength dependence of the optical transmittance and reflectance was recorded, for the as-prepared and the annealed films, in the wavelength range from 350 to 2700 nm using a double beam spectrophotometer. Fundamental optical properties such as absorption coefficient and energy band gap were derived based on the measured spectra and film's thickness. We demonstrate in the present work that the synergy of annealing and thickness reduction can be exploited for light transmittance enhancements, and consequently for optoelectronic applications including transparent conductive electrodes.     

Optical and structural properties of amorphous SexTe100-x aligned nanorods

In the present work, we report studies on optical and structural phenomenon in as-deposited thin films composed of aligned nanorods of amorphous Se_xTe_100-x (x = 3, 6, 9, and 12). In structural studies, field emission scanning electron microscopic (FESEM) images suggest that these thin films contain high yield of aligned nanorods. These nanorods show a completely amorphous nature, which is verified by X-ray diffraction patterns of these thin films. Optical studies include the measurement of spectral dependence of absorption, reflection, and transmission of these thin films, respectively. On the basis of optical absorption data, a direct optical band gap is observed. This observation of a direct optical band gap in these nanorods is interesting as chalcogenides normally show an indirect band gap, and due to this reason, these materials could not become very popular for semiconducting devices. Therefore, this is an important report and will open up new directions for the application of these materials in semiconducting devices. The value of this optical band gap is found to decrease with the increase in selenium (Se) concentration. The reflection and absorption data are employed to estimate the values of optical constants (extinction coefficient (k) and refractive index (n)). From the spectral dependence of these optical constants, it is found that the values of refractive index (n) increase, whereas the values of extinction coefficient (k) decrease with the increase in photon energy. The real and imaginary parts of dielectric constants calculated with the values of extinction coefficient (k) and refractive index (n), are found to vary with photon energy and dopant concentration.     

Modified Envelope Method for Obtaining Optical Properties of Weakly Absorbing Thin Films and Its Application to Thin Films of Pb(Zr,Ti)O3 Solid Solutions

A modified envelope method, which includes the consideration of the light intensity loss from the back surface of the substrate, was developed and shown to be a simple and convenient tool for obtaining the optical properties and the thickness of the film by using the transmission spectra alone in the medium and weak absorption regions. In the near-optical band gap region, both the transmission and the reflection spectra were used to calculate the optical constants of the films. This technique was applied to the thin films of PZT solid solutions across the entire composition range. The film thickness derived from the envelope method was cross-checked by a computer simulation method and was found to have an accuracy better than 2%. In addition, the refractive indices were fitted to a simple Sellmeier-type equation for determining the dispersion constants for PZT films. The valid wavelength range of these dispersion relations was from 350 to 2000 nm. The refractive index of the PZT films decreased linearly with increasing zirconium content. On the other hand, the optical band gap energy of the PZT films increased with increasing zirconium content.     

Porphyrin migration and aggregation in a poly(methylmethacrylate) matrix

The aging of thin polymer films is interesting for the development of nonlinear optical media. In this study, the optical properties of porphyrin‐doped poly(methylmethacrylate) (PMMA) films are investigated before and after annealing. Both absorption and luminescence spectroscopies were used to characterize the changes that occurred during the thermal treatment. The surface and bulk characteristics of the doped films were also measured using atomic force microscopy, X‐ray‐induced photoelectron spectra, and DSC. We found that the aging of the thin polymer films led the porphyrin molecules to diffuse in the direction of the polymer surface. This led to the random formation of porphyrin aggregates on the surface, followed by absorption band shift and little luminescence quenching. These results suggest that porphyrin‐doped PMMA films could be used as long‐term stable active optical materials. POLYM. COMPOS., 35:665–670, 2014. © 2013 Society of Plastics Engineers     

Kinetic model for thermal dehydrochlorination of poly(vinyl chloride)

In this paper, a novel method for calculating degradation kinetics is presented. The method has been applied to the thermal dehydrochlorination of two different samples of PVC. It has been observed that this dehydrochlorination is complex and involves two different processes. A model that accounts for the entire dehydrochlorination is proposed. This model involves nucleation and growth and diffusion controlled mechanisms. The kinetic parameters are obtained from linear heating rate, isothermal and sample controlled thermal analysis experiments. Kinetic results obtained from the macroscopic thermal analysis measurements demonstrate the correlation between the kinetics of the thermal dehydrochlorination of PVC and the structure of this macromolecule.     

Structural,electrical, and linear/nonlinear optical characteristics of thermally evaporated molybdenum oxide thin films

Homogeneous thin films of Molybdenum oxide (MoO₃) were grown on quartz and glass substrates using the thermal evaporation method. XRD results showed that the MoO₃ powder has a polycrystalline structure with an orthorhombic crystal system whereas the MoO₃ thin films have amorphous nature. SEM images showed that the MoO₃ thin films have a nearly uniform surfaces with worm-like shape grains. The film thickness influences on the linear and nonlinear optical characteristics of MoO₃ thin films that were examined using spectrophotometric measurements and from which, the linear optical constants of the MoO₃ thin films were estimated. The electronic transition type was determined as a direct allowed one. The values of the optical band gap were obtained to be in the range of 3.88–3.72 eV. The dispersion parameters, third-order nonlinear optical susceptibility, and the nonlinear refractive index of the MoO₃ thin films were determined and interpreted in the light of the single oscillator model. The temperature dependence of the DC electrical conductivity and the corresponding conduction mechanism for the MoO₃ films were investigated at temperatures ranging from 303 to 463 K.     

Molecular weight distribution in a polymer film degraded by light

An explicit expression is derived for the weight distribution function of polymer molecules in a photodegraded film. A most probable weight distribution of linear molecules is assumed initially present; normally incident, monochromatic light obeying a single Beer-Lambert absorption relation is the photolyzing radiation. The dependence of the weight distribution upon the film's optical thickness and the integrated incident light flux is illustrated by curves computed according to the derived functions. Predicted gel permeation chromatograms are indicated.     

Optical parameters and absorption studies of UV‐irradiated azo dye‐doped PMMA films

PMMA and PMMA films doped with different contents of azo dye have been made by using the casting technique. The absorption spectral analysis showed that the doped films have two absorption bands attributed to the π‐π* and n‐π* transition of chromophore groups. These bands disappear upon UV‐irradiation, suggesting that the studied system undergoes a photo degradation process. The absorption coefficient and optical energy gap (E_g) have been obtained from the absorption edge in the 200–900 nm range. It was found that E_g decreases with increasing doping levels, whereas it increases with increasing irradiation time. The width of the tail of localized states in the band gap (ΔE) was evaluated using the Urbach edge method. Some optical parameters were determined from the reflection and transmission spectra in the spectral range of 200–2500 nm. The dependence of the refractive index on irradiation time and doping level have been discussed. It was found that the photo‐induced refractive index changes are very large. These changes suggest the applicability of the studied system in optical devices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Functional properties of transparent ZnO thin films synthetized by using spray pyrolysis for environmental and biomedical applications

Spray pyrolysis is a promising method for producing thin, transparent films on glass substrates. ZnO thin films synthesized by this method exhibit high crystallinity, adhesion and chemical resistance. They also possess the ability to degrade water pollutants and exhibit antibacterial properties under UV light. The crystalline structure of these films has been studied using grazing X-ray diffraction (GIXRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM), while transmission electron microscopy (TEM) has been used to investigate their composition and purity. Other techniques such as X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and ultraviolet–visible spectroscopy were also employed. ICP-OES was used to evaluate photocatalyst leaching. These transparent thin films have exceptional optical properties, with a transmittance of 95%. The photocatalytic degradation of 4-Nitrophenol (4-NP) by ZnO thin films showed a degradation rate of 94% in 270 min with a kinetic constant value of 3.1 × 10⁻³ mM/min. The films are also highly durable and reusable, exhibiting superior performance compared to other ZnO photocatalysts. The bactericidal activity of these transparent films was also evaluated, with a value of 60.6% being obtained using Escherichia coli after irradiating the films with UV light for 3 h.