Robert T. Graf

Optical Constant Determination of Thin Polymer Films in the Infrared

Thin films of poly(vinyl chloride), poly(methyl methacrylate), and poly(styrene) were analyzed by Fourier transform infrared spectroscopy. The interference fringes present in the transmission spectra of these samples were used to determine film thickness and average refractive index. Subsequent Kramers-Kronig analysis of these transmission spectra provided the dispersion of the refractive index and the absorption index across the entire mid-infrared region. Interference fringes were absent in the optical constant spectra, and good agreement was obtained between our optical constant spectra and those of other authors.

The Influence of Interfacial Structure on the Flexural Strength of E-glass Reinforced Polyester

Abstract Simultaneous mechanical and molecular characterization of a composite system has been attempted with respect to the interface. The mechanical properties of an E-glass cloth/ y-methacryloxypropyltrimethoxysilane (γ-MPS)/bisphenol-A-fumarate polyester resin composite system were studied as a function of the amount of γ-MPS coupling agent present on the glass fiber surface. Fourier transform infrared diffuse reflectance spectroscopy was used to determine the amount and structure of γ-MPS on the glass. This structure consists of two clearly distinguishable regions: physisorbed layers of γ-MPS which can be dissolved by organic solvents, and chemisorbed layers which are insoluble. The physisorbed layers of γ-MPS reduced the strength of the polyester composite. A polymer blend consisting of siloxane oligomer of γ-MPS and bisphenol-A polyester was also investigated as a model of the silane interphase. Results from this model study are in agreement with the polyester composite data.

Polarization Modulation Fourier Transform Infrared Ellipsometry of Thin Polymer Films

Polarization modulation infrared ellipsometric spectra were collected on an FT-IR spectrometer, with the use of two linear polarizers and a photoelastic modulator. Samples consisted of thin poly(vinyl acetate) and poly(methyl methacrylate) films on gold substrates. The relative phase retardation (delta) and relative amplitude (psi) were derived from these measurements. These spectra were superior to those from static infrared ellipsometry measurements on the same samples. The thickness and optical constants of the films were calculated from the ellipsometric measurements and compared with reference optical constant spectra.

Introduction to Optics and Infrared Spectroscopic Techniques

Infrared spectroscopy is one of the oldest techniques for the molecular level characterization of materials, and it has of course been extensively used to study polymer systems. Excellent review articles exist for the application of both dispersive [1] and Fourier transform instrumentation [2] to polymers. The use of IR to study polymer surfaces and interfaces has also been reviewed [3]. As the number and complexity of IR techniques for examining non-routine samples has increased, there has been a growing tendency to examine samples ‘in situ’. This is especially true where polymer systems are involved. Infrared spectra of such systems as filled polymers, glass reinforced plastics, fibers, and surface treated particulates, have been recorded in the past using relatively old techniques such as transmission and ATR. However, the spectral quality was low. Now it is possible to obtain high quality spectra of these systems by using such techniques as diffuse reflectance, photoacoustic, and IR microscopy.

Evaluation of Space Radiator Performance by Simulation of Infrared Emission

The total performance of a droplet space radiator has been predicted by simulation of infrared emission spectra. Emission spectra for a droplet are simulated with the use of exact optical theory from the optical constant spectra of a low-molecular-weight silicone, which is a candidate for use as an emission medium of the radiator. Emissive power and total emittance are calculated from the simulated emission spectra for a droplet at different temperatures. It is found that the fourth-power temperature dependence of the emissive power of the blackbody and the temperature dependence of the emissivity inherent to the materials govern the emissive power of the droplet. The progressive decreases in temperature of a droplet and a droplet sheet in space are also simulated. A droplet with a diameter of 1 μm is predicted to cool from 500 K to 252 K in two seconds. The effects of the size of a droplet and the number density of the droplets in the sheet on the cooling rate are estimated. A smaller droplet is essential for obtaining effective radiation in the liquid droplet radiator. A dense cloud of the droplet sheet will retard the cooling rate of the droplets because of the reabsorption of the emitted light.

Quantitative Analysis of Neat Polymeric Fibers by DRIFTS Using Optical Constant Data

Infrared reflectance spectra were obtained of drawn and undrawn poly(ethylene terephthalate) (PET) fibers using a diffuse reflectance attachment. different fiber alignments with respect to the incident beam produced relative intensity changes for the drawn, but not the undrawn fiber spectra. The band positions in the fiber reflection spectra were shifted with respect to their positions in a transmission spectrum. The intensities of the weak bands and overtones was enhanced in the fiber reflectance spectra as compared to transmission spectra. reflection spectra were also obtained of drawn PET film. The film reflection spectra showed the same band shifts as the fiber reflectance spectra, but the overtone bands were not enhanced as in the fiber case. Using the optical constants measured from a solution-crystallized sample of PET, and a well-known equation from the statistical theory of diffuse reflectance, a fiber reflectance spectrum was calculated. This calculated spectrum agreed quite well with the experimental spectrum of undrawn PET fibers in band positions, relative intensities, and absolute intensities.

Comparison of FT-IR Transmission, Specular Reflectance, and Attenuated Total Reflectance Spectra of Polymers

Thin films of poly(methyl methacrylate) were deposited on germanium substrates and analyzed by Fourier transform infrared spectroscopy. Three types of experiments were performed: transmission, specular reflectance, and attenuated total reflectance. The spectra obtained from these experiments differed in the position, shape, and intensity of the bands even though all the experiments were performed on the same sample. These differences were the result of optical distortion effects. To account for these effects the optical constants of the polymer were determined and the expected band profiles for each experiment were calculated. The calculated and experimental spectra agreed well in both position and intensity of the bands.

Fourier Transform Infrared Ellipsometry Of Thin Polymer Films

Reflection spectra containing phase as well as intensity information were collected on a FT-IR spectrometer using two linear polarizers. The sample consisted of a poly(vinyl acetate) (PVAc) film on a copper substrate. Using well known principles of ellipsometry, the relative phase retardation (delta) and relative amplitude (psi) were calculated from these measurements.

Fourier Transform Infrared Surface Electromagnetic Wave Spectroscopy of polymer thin films on metal substrate

FT-IR Surface Electromagnetic Wave Spectroscopy utilizing the Otto configuration is applied to the study of a thin film of polyvinyl acetate) on a copper substrate. Multiple reflection modification was effective to enhance the sensitivity of this technique.