Glen F. Bailey

Water in polymer membranes. Part I : Water sorption and refractive index of cellulose acetate

Abstract The dependence of water absorption of 2 to 4 μm thick membranes of cellulose acetate on relative humidity was determined by measuring small changes in their asymmetric waveguide properties in the visible spectral region. Simultaneous measurements of changes in film thickness provide a direct method for obtaining the change in film volume as a function of water concentration and a new measure of polymer porosity. Data are presented for a typical film fabricated from cellulose acetate (CA398-30) which illustrate the usefulness of studying water absorption by integrated optics techniques.

Water in polymer membranes. Part II : Raman scattering from guided laser beams

Abstract Simultaneous application of integrated optics and Raman spectroscopy is used to investigate the hydrogen bonding of water in thin dense symmetric membranes of cellulose acetate (CA). A modified X-ray quarter circle goniometer is used to measure refractive index, film thickness, and Raman spectra using guided laser beams and the prism coupler technique. The film remains in a fixed position during all measurements thereby ensuring identical light collection geometries for Raman scattering observed from different wave-guiding modes. To illustrate the technique, Raman scattering of a 3.5 μm film of CA398-10 in the OH stretching region is shown as a function of relative humidity (RH). These spectra show that water sorbed at less than 50% RH is weakly hydrogen-bonded but above 50% RH, sorbed water has the strongly hydrogen-bonded properties of bulk water.

Water in polymer membranes. Part III : Water sorption and pore volume in cellulose acetate films

Abstract Changes in waveguide properties of several cellulose acetate membranes and one polyimide membrane were measured as a function of their exposure to varying levels of relative humidity. The volume fraction of water in the films and the occupied pore volumes were determined from refractive index and thickness changes. The dependence of the refractive index on water absorption is related to a competition between two processes: one of filling pores with no film expansion and one of “free expansion” where the film expands to completely accommodate the added water volume. The term “pore” is taken to mean a volume with molecular and not macroscopic dimensions. The hydration properties of these dense cellulose acetate membranes were affected by degree of acetylation, casting temperatures and annealing treatments. Annealing CA398 membranes at 180°C decreased film water concentration by reducing the amount of free expansion. Annealed CA398 membranes that were tested in a reverse osmosis cell were found to have high salt rejection compared to unannealed films. The hydration characteristics of a polyimide membrane are compared to cellulose acetate membranes.

Divergence Errors in Raman Depolarization Measurements of Liquids in Capillary Cells

The source of errors in depolarization measurements using laser excitation and their dependence on monochromator, image magnification, and cell geometry is considered. Two common ways of measuring these ratios are considered, and the extent of the expected divergence errors in capillary cells is calculated for the 90° scattering geometry. It is shown that the ratio ρn determined by rotating the laser polarization from perpendicular to parallel to the scattering direction is subject to errors which limit its usefulness for highly polarized lines but is acceptable for depolarized lines. Use of an analyzer gives depolarization ratios ρs with the highest accuracy.

High-pressure liquid chromatography and ultraviolet spectrometry of ketonic C27 sterols

A method for the separation of ketonic C27 sterols was devised, based on high-pressure liquid chromatography (HPLC) and ultraviolet absorption (UV). The adsorption column contained silica gel, particle size 10 μm, and the eluents were dichloromethane/n-hexane/ethyl acetate (94∶5∶1) and dichloromethane/ethyl actate (99∶1) followed by dichloromethane/ethyl acetate (3∶1). The 5β-sterols were eluted before the 5α-analogs, sterols with isolated double bonds before conjugated carbonyl compounds, and ketones before hydroxy ketones. The effect of carbonyl groups on polarity depends on the position in the molecule and decreases in the order C-3>C-6>C-7. The ultraviolet absorption spectra of eleven sterols were determined, and their absorbance at 254 nm and at 280 nm was used for analyzing the column effluent with a dual detector system.

Compensated Polarization Scrambler for Raman Depolarization and Intensity Measurements on Microsamples

Abstract It has long been recognized 1,2,3,4,5 in measuring relative intensities and depolarization ratios of Raman lines that prism and grating spectrometers have different transmittances for light polarized parallel (T∥) and perpendicular (T⊥) to the slit. Several methods have been used to give equal instrument response to parallel and perpendicular polarization. Stitt and Yost3 used a Nicol prism parallel to the high-transmittance direction of the spectrometer, combined with a rotatable mica half-wave plate to transmit either vector to the Nicol prism. This method has the advantage of having a higher spectrometer transmittance, but the mica plate gives exact half-wave retardation at only a single wavelength. A mica quarter-wave plate 4,5 averages the transmittances of the spectrometer for the two polarization directions, but is also wavelength dependent. Virtually achromatic circular polarizers have been designed and constructed 6,7, but these devices are too bulky and expensive for the clear apertures...