Thick Films Of Poly Research Articles

ATR-FTIR spectroscopy combined with machine learning for classification of PVA/PVP blends in low concentration

The use of Fourier transformed infrared spectroscopy (FTIR) and multivariate analysis for sample classification has been extensively explored in the literature. The overall accuracy obtained in most of the studies raises questions about their reliability due to technical limitations and misuse of the analysis driving to overfitting/underfitting of data. There are established procedures to avoid overfitting/underfitting, but there is a lack of studies to understand the relationship between the limitation of the data provided by the FTIR and the associated method of analysis for sample classification. In this study, FTIR spectra were obtained from thick films of poly (vinyl alcohol) (PVA)/poly (vinyl pyrrolidone) (PVP) polymeric blends, with PVP concentrations below 3% (wt./wt.). We analyzed the FTIR spectra by using simple algorithms for sample classification to evaluate the predicting model accuracy at low concentrations of PVP into the PVA matrix. The raw data were submitted to pre-treatment by standard normal variate (SNV), and different spectral ranges were explored by principal component analysis (PCA). Then, PCA and FTIR-SNV data were used for supervised analysis by using linear discriminant analysis (LDA); k-nearest neighbors (KNN); and support vector machines (SVM) algorithms. The method was able to classify samples with 0.1 wt% of PVP with an overall accuracy of 100% with quadratic SVM by the proper choice of the spectral range and number of PCs. Finally, we show that the FTIR associated with multivariate analysis can be used for sample classification at low concentration changes.

Spatial distribution of single guest molecules along thickness of thin films of poly(2-hydroxyethyl acrylate).

We have investigated three-dimensional distribution and diffusion behaviors of single guest dyes in 1-µm thick films of poly(2-hydroxyethyl acrylate) (PHEA) by using astigmatism imaging method. Perylene diimide derivative (BP-PDI) in the PHEA films localized along the Z-axis at ca. Z = 600-700nm distant from the interface (Z = 0) between PHEA and glass substrate. This Z-localization was not observed in different polymer films of poly(methyl methacrylate) (PMMA), poly(methyl acrylate) (PMA), and polystyrene (PSt). Because the glass transition temperature of the PHEA is lower than the room temperature, BP-PDI in the PHEA films exhibited Brownian motion, normal diffusion on the XY plane and confined motion along the Z-direction. For elucidating the mechanism of the peculiar localization of the guest dyes along film thickness in the PHEA films, we measured diffusion behaviors of different dyes, R6G and Atto 488, in 1-µm thick PHEA films, obtaining result that the Z-distributions of the dyes were overall similar to that of BP-PDI. The result indicates that the Z-localization of the guest dyes should be ascribed not to the interaction between glass surface and guest dye but mainly to the Z-dependent property of the PHEA film. Indeed, the lateral diffusion coefficients of the guest dyes depended on their Z-positions.

Investigating the effects of pyridine and poly(4-vinylpyridine) on CO2 reduction electrocatalysis at gold electrodes using in situ surface-enhanced Raman spectroelectrochemistry.

The CO2 reduction reaction (CO2RR) at metal electrodes is altered in the presence of pyridine and related species. Thick films of poly(4-vinylpyridine) on Au electrodes result in large current enhancements at low applied potentials but do not enhance CO2RR at these potentials. Surface-enhanced Raman spectroelectrochemistry can probe CO2-surface interactions and reveals that desorption of CO2 as bicarbonate is retarded in the presence of 4-PVP, with implications for ion-transport limitations in thick film CO2RR.

Local Thermomechanical Analysis of a Microphase-Separated Thin Lamellar PS-b-PEO Film

We use atomic force microscopy (AFM) and hot tip AFM (HT-AFM) to thermophysically characterize a 30 nm thick film of poly(styrene-block-ethylene oxide), PS-b-PEO, and to modify its lamellar patterns having spacing of 39 ± 3 nm. AFM tip scans of the polymer film induce either abrasive surface patterns or nanoscale ripples, which depend upon the tip force, temperature, and number of scans. The evolution of the lamellar patterns is explained by the polymer film molecular structure and mode I crack propagation in the polymer combined with the stick-and-slip behavior of the AFM tip. The HT-AFM measurements at various tip-sample temperatures and scanning speeds yield several thermophysical quantities: the PEO melting temperature of 54 ± 12 °C, the PS glass transition temperature of 54 ± 12 °C, the PS-b-PEO specific heat of 3.6 ± 2.7 J g(-1) K(-1), the PEO melting enthalpy of 111 ± 88 J g(-1), and the free energy of Helmholtz for PEO unfolding (and melting) of 10(-20) J nm(-2). These quantities are obtained for PS-b-PEO volumes of 30,000 nm(3), which correspond to 30 ag of the polymer.

Quantitative analysis of perfumes in talcum powder by using headspace sorptive extraction

Quantitative analysis of perfume dosage in talcum powder has been a challenge due to interference of the matrix and has so far not been widely reported. In this study, headspace sorptive extraction (HSSE) was validated as a solventless sample preparation method for the extraction and enrichment of perfume raw materials from talcum powder. Sample enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnetic stir bar incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace vial by using a holder. The stir bar is then thermally desorbed online with capillary gas chromatography-mass spectrometry. The HSSE method is based on the same principles as headspace solid-phase microextraction (HS-SPME). Nevertheless, a relatively larger amount of extracting phase is coated on the stir bar as compared to SPME. Sample amount and extraction time were optimized in this study. The method has shown good repeatability (with relative standard deviation no higher than 12.5%) and excellent linearity with correlation coefficients above 0.99 for all analytes. The method was also successfully applied in the quantitative analysis of talcum powder spiked with perfume at different dosages.

Dopping Effect on Optical Constant of Poly (Vinyl Chloride)

Thick films of poly(vinyl chloride)(PVC)& PVC doped with Zn(etx)2 salt complex have been prepared by cast method with fixed thickness almost (120±5) Microns. Optical studies were carried out in the wavelengths region(200-900)nm based on absorption & transmition measurement. Optical parameters such as absorption coefficient(?) ,refraction index(n) and extinction coefficient(K) were observed to be effected by adding the dopant.Electrical parameters such as real(?)& imaginary(?) part of dielectric constant were also calculated part of dielectric constant were also calculated from the optical parameters using Maxwell equation.

Dopping Effect on Optical Constant of Poly (Vinyl Chloride)

Thick films of poly(vinyl chloride)(PVC)& PVC doped with Zn(etx)2 salt complex have been prepared by cast method with fixed thickness almost (120±5) Microns. Optical studies were carried out in the wavelengths region(200-900)nm based on absorption & transmition measurement. Optical parameters such as absorption coefficient(?) ,refraction index(n) and extinction coefficient(K) were observed to be effected by adding the dopant.Electrical parameters such as real(?)& imaginary(?) part of dielectric constant were also calculated part of dielectric constant were also calculated from the optical parameters using Maxwell equation.

Morphological and mechanical characterization of a PMMA/CdS nanocomposite

Thick film of poly(methyl methacrylate) (PMMA)/CdS nanocomposite have been synthesized by the solution casting process. The nanostructure of the CdS particles has been ascertained through the small angle X-ray scattering (SAXS) technique. The surface morphological characterization of the PMMA/CdS nanocomposite has been done through scanning electron microscopy (SEM) analysis. The variation of mechanical loss factor (Tanδ) with temperature and tensile properties of prepared samples have been studied using Dynamic Mechanical Analyzer (DMA). This study reveals that the glass transition temperature (T g), Young’s modulus, and fracture energy of the PMMA/CdS nanocomposite are greatly influenced by the existence of interfacial energetic interaction between dispersed CdS nanoparticles and the matrix of PMMA.

Formation of convex shaped poly(phenylsilsesquioxane) micropatterns on indium tin oxide substrates with hydrophobic-hydrophilic patterns using the electrophoretic sol-gel deposition method

Hydrophobic-hydrophilic patterns were formed on indium tin oxide substrates, and thick films of poly(phenylsilsesquioxane) (PhSiO3/2) particles, prepared by the sol-gel process, were selectively deposited onto hydrophilic areas of the substrates by electrophoresis. The films composed of PhSiO3/2 particles became transparent with morphological changes from aggregates of particles to a continuous phase after a heat treatment. After heat treatment at 200 °C, convex-shaped PhSiO3/2 micropatterns were formed on the hydrophilic region of the pattern. Moreover, the height of micropatterns was controlled by the deposition time. This patterning technique has a wide variety of applications such as fabrication of micro-optical components.

Adhesion of amorphous polymers as a function of temperature probed with AFM force–distance curves

Force–displacement curves have been obtained with a commercial atomic force microscope at different temperatures and probe rates on a thick film of poly( n-butyl methacrylate) and on two films of polystyrene with different molecular weight. In a previous publication [B. Cappella, S.K. Kaliappan, H. Sturm, Macromolecules 38 ( 2005 ) 1874 ] the analysis of force–displacement curves has been focused on the stiffness and on the Young's modulus of the samples. In the present publication we consider the temperature dependence of the work of adhesion. We have obtained master curves of the work of adhesion at fixed maximum loads and, by comparing the results of the two analysis, we show that the work of adhesion follows the Williams–Landel–Ferry equation with the same coefficients previously found for the Young's modulus. Furthermore, we show that the temperature dependence of the work of adhesion of the polymers is a consequence of the temperature dependence of the tip–sample contact area and in the end of the temperature dependence of the stiffness and of the elastic–plastic properties of the samples.

Using AFM Force−Distance Curves To Study the Glass-to-Rubber Transition of Amorphous Polymers and Their Elastic−Plastic Properties as a Function of Temperature

Force−displacement curves have been obtained with a commercial atomic force microscope (AFM) at different temperatures and probe rates on a thick film of poly(n-butyl methacrylate) (PnBMA). The analysis of the force−displacement curves has been focused on the contact portion of the curves, giving information about the stiffness of the sample and its Young's modulus. A novel model of sample deformations that extends the basic equations of the elastic continuum contact theories to the plastic deformations is presented. This model gives several insights into the processes of deformation of soft samples and permits to calculate not only the parameters of the Williams−Landel−Ferry equation but also the Young's modulus and the yielding force of the polymer as a function of temperature and/or probe rate. These quantities have been measured in a wide range of temperatures (70 K) and probe rates (6 decades) for the first time with the AFM, and the results are in very good agreement with measurements performed with...

CO2-Enhanced Transport of Small Molecules in Thin PMMA Films

Steady-state fluorescence measurements have been used to measure the rate of transport of a fluorescent probe (pyrene) out of ca. 200−340 nm thick films of poly(methyl methacrylate) (PMMA) in contact with supercritical CO2 at pressures in the range 34−76 bar (estimated CO2 content in the film from 0.06 to 0.17 weight fraction) and several temperatures (35, 50, and 65 °C). At constant temperature, the estimated pyrene diffusion coefficient increases by approximately 4 orders of magnitude from the lowest to the highest CO2 content (e.g., from ca. 5 × 10-15 cm2/s for ca. 0.08 CO2 weight fraction to ca. 10-10 cm2/s for ca. 0.17 CO2 weight fraction at 35 °C). We compare the present results to our earlier study of CO2-swollen polystyrene (PS) and find: (1) For similar pressures of CO2 at the same temperature, the enhancement of the pyrene diffusion coefficient is larger in PMMA than in PS, presumably as a consequence of the higher solubility of CO2 in PMMA; and (2) at similar CO2 contents, the pyrene diffusion...

Headspace sorptive extraction (HSSE), stir bar sorptive extraction (SBSE), and solid phase microextraction (SPME) applied to the analysis of roasted Arabica coffee and coffee brew.

Headspace sorptive extraction (HSSE) and stir bar sorptive extraction (SBSE), two recently introduced solventless enrichment techniques, have been applied to the analysis of the headspace of Arabica roasted coffee and of the headspace of the brew and of the brew itself. In both HSSE and SBSE enrichment is performed on a thick film of poly(dimethylsiloxane) (PDMS) coated onto a magnet incorporated in a glass jacket. Sampling is done by placing the PDMS stir bar in the headspace (gas phase extraction or HSSE) or by immersing it in the liquid (liquid phase extraction or SBSE). The stir bar is then thermally desorbed on-line with capillary GC-MS. The performance of HSSE and SBSE have been compared through the determination of the recoveries and relative abundances of 16 components of the coffee volatile fraction to classical static headspace (S-HS) and to headspace and in-sample solid phase microextraction (HS-SPME and IS-SPME, respectively) applying the fibers PDMS 100 microm, Carbowax/divinylbenzene 65 microm (CW/DVB), Carboxen/PDMS 75 microm(CAR/PDMS), polyacrylate 85 microm(PA), PDMS/divinylbenzene 65 microm(PDMS/DVB), and Carboxen/divinylbenzene/PDMS 50-30 microm(CAR/PDMS/DVB). In all cases, HSSE and SBSE gave higher recoveries, and this is entirely due to the high amount of PDMS applied.

Photochemical Attachment of Polymer Films to Solid Surfaces via Monolayers of Benzophenone Derivatives

We report a simple and yet effective way to photochemically attach thin polymeric layers to solid surfaces. The system is based on a photoreactive benzophenone derivative that is bound to SiO2 surfaces via a silane anchor. This substrate is then covered with a polymer film that is reacted with the benzophenone moieties by illumination with UV light (λ > 340 nm). As a result of the photochemical reaction, a thin layer of the polymer is covalently bound to the surface. Nonattached polymer is removed by extraction. As examples, we have successfully attached thin layers of poly(styrene) and poly(ethyloxazoline). The thickness of the layer is a function of the illumination time and the molecular weight of the polymer. The film thickness increases linearly with the radius of gyration of the polymers used for attachment. Using this system, we were able to photochemically attach up to 16 nm thick films of poly(styrene).

Electrical conductivity during XPS of heated PMMA: detection of core line and valence band tacticity effects

Electrical conductivity during the XPS of ∽100 nm thick films of poly(methyl methacrylate) (PMMA) on silicon was induced by heating to above 100°C. Rapid x-ray-induced depolymerization set in at about the same temperature. The electrical conductivity allowed acquisition of high-resolution core line and valence band spectra from s- and i-PMMA, free of differential charging effects. Within a time-scale of ∽25 min the depolymerization did not affect the appearance of the spectra. The presence of methoxy groups at the uppermost surface of the two heated samples was confirmed by angle-dependent XPS, with an indication of a higher surface concentration of such groups for the s-polymer. At ambient temperature the valence band spectra of the two stereoisomers were identical, but when heated to above 100°C a difference of ∽0.15 eV developed in the O 2s binding energies; this is interpreted as being due to preferential crystallization of the s-polymer. Copyright © 1999 John Wiley & Sons, Ltd.

Optical charge carrier generation in a conjugated polymer

Stationary photoconduction was measured on 100 nm thick films of poly(methylimino-1,4-phenylene-1-phenyl-1,2-ethenylene-2,5-dimethoxy-1,4-phenylene-2-phenyl-1,2-ethenylene-1,4-phenylene) sandwiched between indium tin oxide and aluminium electrodes. Bulk photoionization was observed upon irradiating through the positively biased aluminium electrode. For photon energies 2.6 eV < hv < 3.2 eV either defect catalyzed or intrinsic dissociation of relaxed singlet excitations prevails. For hv > 3.2 eV the carrier yield increases with excess photon energy due to intrinsic photoionization. The functional dependencies on electric field and photon energy are in accord with the 3D version of Onsager's theory of geminate pair dissociation implying a geminate pair distance that increases with hv. As an ionizing event, coupling between the non-relaxed initial Franck-Condon state with an mAg state is involved. Further increase of the yield correlates with the onset of optical absorption to the third optically allowed Bu state.

Optical charge carrier generation in a conjugated polymer

Stationary photoconduction was measured on 100 nm thick films of poly(methylimino-1,4-phenylene-1-phenyl-1,2-ethenylene-2,5-dimethoxy-1,4-phenylene-2-phenyl-1,2-ethenylene-1,4-phenylene) sandwiched between indium tin oxide and aluminium electrodes. Bulk photoionization was observed upon irradiating through the positively biased aluminium electrode. For photon energies 2.6 eV < hv < 3.2 eV either defect catalyzed or intrinsic dissociation of relaxed singlet excitations prevails. For hv > 3.2 eV the carrier yield increases with excess photon energy due to intrinsic photoionization. The functional dependencies on electric field and photon energy are in accord with the 3D version of Onsager's theory of geminate pair dissociation implying a geminate pair distance that increases with hv. As an ionizing event, coupling between the non-relaxed initial Franck-Condon state with an mAg state is involved. Further increase of the yield correlates with the onset of optical absorption to the third optically allowed Bu state.

Nanomosaic Surfaces by Lateral Phase Separation of a Diblock Copolymer

Ultrathin films of symmetrical polystyrene-block-poly(2-vinylpyridine) diblock copolymer with a degree of polymerization of 600 were prepared by spin coating from a nonselective solvent, i.e., CHCl 3 , on mica. The concentration of the casting solutions was chosen to be too low to allow homogeneous coverage of the substrate without significant stretching of the macromolecules. Scanning force microscopy demonstrated the formation of uniform polystyrene clusters with a height of about 5 nm and a distance of about 100 nm between them. In between the substrate was covered by 1 nm thick film of poly(2-vinylpyridine). The large periodicity of the two-dimensional phase pattern is explained by the strong interaction of poly(2-vinylpyridine) with mica, favoring a highly stretched conformation. X-ray photoelectron spectroscopy showed that about every third poly(2-vinylpyridine) unit was in chemical contact with the substrate. When the film thickness was increased, the X-ray photoelectron spectroscopy N(ls) signal decreased in comparison to the C(ls) signal indicating that the adsorbed poly(2-vinylpyridine) got increasingly covered by polystyrene. An estimation of the free energy indicates that the lateral phase separation is mainly controlled by the length of the polystyrene blocks affecting the incompatibility of the polystyrene and the poly(2-vinylpyridine) covered mica.

Ultraviolet and visible spectroscopy of poly(paraphenylene vinylene)

The UV–visible spectrum of 200 nm thick films of poly(p-phenylene vinylene) (PPV) shows three absorption bands, with maxima at 6.12, 5.06, and 3.09 eV. The first two absorption bands are related to localized molecular states while the band at 3.08 eV has a more complicated character with a 1.5 eV bandwidth, a 2.49 eV band edge and a maximum absorption coefficient of 1.5×105 cm−1. Semiempirical MO calculations at the INDO and PPP levels and VEH techniques have been applied in an interpretation of the electronic structure and excitations in this electrically conducting polymer. A description of the lower energy excited states of PPV has been achieved using an exciton model in which the polymer chain is treated as an ordered array of identical molecules. The 3.08 eV polymer absorption band is then attributed to an electron excitation spread over several monomer units strongly perturbed by electronic–vibrational coupling.

A LASER INTERFEROMETER FOR MONITORING THIN FILM PROCESSES: APPLICATION TO POLYMER DISSOLUTION

Abstract An instrument has been assembled which is well suited for monitoring changes in transparent films and coatings where the thickness ranges from several μm down to fractions of a μm. The operation is based on thin film optical interferometry. Applications include measurement of the dissolution rate in selected organic solvents of a 2-μm thick film of poly(methyl methacrylate) (PMMA) which has been coated on a silicon-oxide-surfaced silicon wafer. Such measurements are often required in developing images from electron-beam or X-ray exposure in microlithography and microelectronics. An unpolarized light beam from a 2 mW He-Ne laser is directed obliquely onto the surface of the film. From the time dependence of the intensity of reflected light, both the rate of dissolution and the refractive index of the film can be ascertained. A review of the optical theory upon which such measurements are based is included. The scope of additional information obtainable through application of this technique, includ...