Polymer Films Of Different Thicknesses Research Articles

New Insight into the Mechanism of Drug Release from Poly(d,l-lactide) Film by Electron Paramagnetic Resonance.

A novel approach based on convolution of the electron paramagnetic resonance (EPR) spectra was used for quantitative study of the release kinetics of paramagnetic dopants from poly(d,l-lactide) films. A non-monotonic dependence of the release rate on time was reliably recorded. The release regularities were compared with the dynamics of polymer structure changes determined by EPR, SEM, and optic microscopy. The data obtained allow for the conclusion that the main factor governing dopant release is the formation of pores connected with the surface. In contrast, the contribution of the dopant diffusion through the polymer matrix is negligible. The dopant release can be divided into two phases: release through surface pores, which are partially closed with time, and release through pores initially formed inside the polymer matrix due to autocatalytic hydrolysis of the polymer and gradually connected to the surface of the sample. For some time, these processes co-occur. The mathematical model of the release kinetics based on pore formation is presented, describing the kinetics of release of various dopants from the polymer films of different thicknesses.

Birefringence in solutions and films of poly[4,4'-bis(4''-N-phenoxy)diphenylsulfon]imide of 1,3 bis(3',4-dicarboxyphenoxy)benzene

Birefringence in solutions and films of poly[4,4'-bis(4''-N-phenoxy)diphenylsulfon]imide of 1,3-bis(3',4-dicarboxyphenoxy)benzene macromolecules is studied. The method of birefringence in the flow of polymer solutions in DMF allows one to determine the proper specific optical anisotropy of the repeating unit of chain βM = +15 × 10–27 cm3 mol/g. Spontaneous birefringence in polymer films of different thickness is studied under various incidence angles of a polarized beam. The total data analysis allows one to estimate the orientation order parameter of polymer chain fragments in the vicinity of surface S 0 =–0.01, which is typical of flexible-chain polymers.

Nafion Coated Silver Amalgam Electrode for Determination of Trace Metals by Anodic Stripping Voltammetry

AbstractThis paper describes characterization and application of Nafion coated solid silver amalgam electrodes to prevent surface fouling of surfactants in determination of trace metals by differential pulse anodic stripping voltammetry (DPASV). Polymer films of different thickness were tested using Nafion solutions in the range 0.25%–1%. Optimum thickness was archived using a 0.5% Nafion solution, resulting in both increased response and stability over time compared to uncoated electrodes. The influence of model surface active macromolecules was studied using triton X‐100, sodium dodecyl sulfate, dodecyl pyridinium chloride and bovine serum albumin as representatives for surfactants. The resistance to surfactants makes the studied Nafion coated solid silver amalgam electrodes an interesting alternative for practical use in environmental monitoring.

Potential and film thickness dependence of the photoluminescence of aryl amine polymers

The fluorescence of polyaniline (PANI) and poly(2-methoxyaniline) (PMOA) films has been studied as a function of potential and film thickness. The fluorescence measurements were conducted on polymer films of different thicknesses on platinum electrodes. Absorption spectra were also recorded, using PANI films on semitransparent gold electrodes. The fluorescence emission intensity, in the reduced state as a function of polymer film thickness (measured through the voltammetric charge) shows a complex behaviour. For low thicknesses, none or minimum emission is observed; this is attributed to the metallic quenching of the fluorescence. Beyond a critical thickness, the emission increases sharply, then reaches a maximum and finally decays slightly towards a limiting value. The decay is interpreted as due to the attenuation of the waves reflected on the metal surface: both the excitation wave absorbed after being reflected, and the emitted one reaching the detector after reflection are exponentially attenuated as the film thickness increases. In the case of PMOA, a polymer that, depending on the synthesis conditions, shows either conducting or non-conducting (redox) behaviour, the conducting form has a fluorescence response similar to that of PANI, whereas the non-conducting form shows low emission.

Demonstrating the feasibility of monitoring the molecular-level structures of moving polymer/silane interfaces during silane diffusion using SFG.

In this paper, the feasibility of monitoring molecular structures at a moving polymer/liquid interface by sum frequency generation (SFG) vibrational spectroscopy has been demonstrated. N-(2-Aminoethyl)-3-aminopropyltrimethoxysilane (AATM, NH2(CH2)2NH(CH2)3Si(OCH3)3) has been brought into contact with a deuterated poly(methyl methacrylate) (d-PMMA) film, and the interfacial silane structure has been monitored using SFG. Upon initial contact, the SFG spectra can be detected, but as time progresses, the spectral intensity changes and finally disappears. Additional experiments indicate that these silane molecules can diffuse into the polymer film and the detected SFG signals are actually from the moving polymer/silane interface. Our results show that the molecular order of the polymer/silane interface exists during the entire diffusion process and is lost when the silane molecules traverse through the thickness of the d-PMMA film. The loss of the SFG signal is due to the formation of a new disordered substrate/silane interface, which contributes no detectable SFG signal. The kinetics of the diffusion of the silane into the polymer have been deduced from the time-dependent SFG signals detected from the AATM molecules as they diffuse through polymer films of different thickness.

Analysis of the Elastic Modulus of a Thin Polymer Film

AbstractThis paper discusses the interaction between mechanical properties of a thin layer and those of its substrate. The underlined questions are: how the substrate's mechanical properties affect those of the film; how the layer's thickness affects its mechanical properties. Nanoindentation tests were performed on polymer films of different thicknesses deposited onto a silica substrate. The mechanical response of such a system is known to be a composite response (film+substrate). Our aim is to understand the elastic behavior of the film inside this structure.Model was used to estimate the elastic modulus of the film from the global measured value. For thin and “compliant” polymer layers deposited on “hard” substrates, an increase of the film elastic modulus was observed along indentation. We attribute this increase to the “anvil effect”: the bulk elastic modulus increases with the hydrostatic pressure which results from the compression of the film. In conclusion, one first interpretation is proposed to understand specific behavior of thin soft polymer layers on rigid substrates.

Kinetics of electron transfer between Fe(CN) 63−/4− and poly(3,4-ethylenedioxythiophene) studied by electrochemical impedance spectroscopy

The electron transfer between the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and the Fe(CN) 6 3−/4− redox couple in aqueous solution was investigated by electrochemical impedance spectroscopy (EIS). PEDOT was electrochemically deposited on platinum from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M poly(sodium 4-styrenesulfonate) (NaPSS) as supporting electrolyte. Pt/PEDOT(PSS) electrodes with polymer films of different thickness were investigated at different concentrations of the redox couple in 0.1 M KCl background electrolyte solution. Impedance spectra were obtained at the dc-potential corresponding to the formal redox potential of Fe(CN) 6 3−/4− ( E°′≈220 mV) where the polymer is in the oxidized and electrically conducting state. The EIS data for the electrodes were fitted to an equivalent electrical circuit. The standard rate constant ( k o) for electron-transfer between Pt/PEDOT(PSS) and Fe(CN) 6 3−/4− was determined by calculations based on the Butler–Volmer equation. The diffusion coefficient ( D) of the redox couple was also calculated from the EIS data.

Single Pass Laser Cutting of Polymers

Since the early 1980's discovery of the ability of excimer lasers to etch polymers precisely and cleanly with minimal thermal damage, excimer lasers have been used actively in the semiconductor industry for various manufacturing processes. In the present study a process for laser cutting of polymers has been investigated. A laser beam of controlled cross-sectional shape is imaged onto a polymer surface. The geometry of the cutting path is controlled by precise movement of a sample mounted on a 2-axis computer controlled work stage. This type of a process is useful for applications such as selective laser cutting or laser marking of polymers. A parametric study of laser cutting of polymers using a 30 watt average power, 308 nm wavelength, XeCl pulsed laser was carried out. The effect of incident laser fluence and laser frequency were studied to determine maximum single pass cutting speed for a given thickness of polymer. Three different types of polymers were studied. Polymer films of different thickness were spin-coated on a silicon wafer and were cured to their respective full cure temperature. Polymer thicknesses from 7 microns to 38 microns were studied. Incident laser fluence was varied from 200 mj/cm2 to 1.0 J/cm2. Laser frequency was varied from 1 Hz to 50 Hz. An analytical formula for optimum single pass cutting speed as a function of the etch rate of a polymer, laser frequency, laser beam length in cutting direction, and polymer thickness was developed. Experimental results obtained indicate that cutting speed is directly proportional to the incident laser fluence and laser frequency, and is inversely proportional to polymer thickness. Predictions of optimum cutting speed obtained from the analytical formula for different polymers were in good agreement with the experimentally measured values.