Optical rheometry of multicomponent polymer liquids

Recent advances in optical rheometric techniques are described, and applications of the methods are presented that motivate their use in elucidating the structure and dynamics of complex, polymeric liquids. Spectroscopic methods, such as infrared dichroism and 2-dimensional Raman scattering, which provide information concerning bond-level orientation dynamics are presented. In addition, the combination of birefringence and stress measurements is demonstrated to be capable of extracting the component dynamics in some multicomponent systems. Examples of the use of these methods include orientation in block copolymers and compatible blends.     

Adsorption and decomposition of H2S on the Ge(100) surface

The adsorption and decomposition of H₂S on the Ge(100) surface is investigated. H₂S is a simple sulfur containing molecule that eventually decomposes to yield hydrogen gas and deposits sulfur on the germanium surface. The surface reactions of H₂S are investigated by ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, and temperature programmed desorption. Room temperature exposure of H₂S to Ge(100) results in dissociative adsorption which can be followed easily by ultraviolet photoelectron spectroscopy. Warming the H₂S exposed surface results in some molecular desorption and further decomposition of the adsorbed species. At saturation, 0.25 ML of H₂S decomposes generating 0.5 ML of atomic hydrogen. Above the hydrogen desorption temperature some etching of the germanium surface is observed by sulfur. The etch product, GeS, is subsequently observed in temperature programmed desorption experiments. Exposure of H₂S to the Ge surface at elevated temperatures leads to higher sulfur coverages. A sulfur coverage approaching 0.5 ML can be deposited at the higher exposure temperatures.     

Duality for semigroup rings

Given a square n-matrix F and an n-row matrix G, pole-shifting problems consist in obtaining more or less arbitrary characteristic polynomials for F+GK, for suitable (“feedback”) matrices K. A review of known facts is given, various partial results are proved, and the case n = 2 is studied in some detail.     

The dynamics of dilute colloidal suspensions subject to time-dependent flow fields by conservative dichroism

An apparatus is described which permits simultaneous determination of the conservative linear dichroism and the average orientation angle of a dilute suspension of optically anisotropic, nonabsorbing spheroids subjected to a transient shear field. The magnitude of the dichroism reflects the degree of alignment of the particles along their average orientation angle and measurement of this property in time directly obtains the rotational motion of the particles. This experiment makes use of a photoelastic modulator in a novel optical train; the first and second harmonics of the detector signal, which are independent functions of the dichroism and orientation angle, are measured simultaneously as functions of time. Preliminary data on a dilute suspension of bentonite in 90% glycerine and 10% water subjected to an instantaneous simple shear are presented to illustrate the technique. The qualitative features of these data are adequately described by the Rayleigh scattering theory coupled with Jeffery's solution for the dynamics of a rigid spheroid in a creeping simple shear.     

Study of the magnetic superconductor,Y9Co7, at high pressure and high magnetic field

We have measured the electrical resistance and magnetic susceptibility of the magnetic superconductor, Y_gCo₇, at pressures up to 20 kbar and in magnetic fields up to 6T. We have found that pressure suppresses the magnetism resulting in a higher superconducting transition temperature and conclude that Y₉Co₇ is an itinerant ferromagnet, not a spin-glass. Pressure also sharpens the superconducting transition and increases the critical magnetic field, signifying that the long range ferromagnetic and superconducting order parameters co-exist but vary spatially. For pressures greater than 6 kbar, the magnetoresistance is always positive, further indicating the suppresion of magnetism by high pressure.     

Uniaxial and biaxial extensional viscosity measurements of dilute and semi-dilute solutions of rigid rod polymers

Effective uniaxial extensional and biaxial extensional viscosities of dilute and semi-dilute solutions of collagen, a rigid rod molecule, have been measured with an opposing jet apparatus. The concentration of collagen in the glycerin/water solvent ranged from 50 to 2300 ppm. The data agree quantitatively with a theory developed by Batchelor describing the extensional viscosity of perfectly aligned rigid rods. The viscosity measured for the dilute rigid rod solutions is independent of the rate of strain as predicted by Batchelor's theory. Data taken on the semi-dilute, strain-thinning solutions at strain rates sufficiently high to align the rods in the extension direction also agree with the predictions of Batchelor's theory. The measured viscosity of semi-dilute solutions at low strain rates agree qualitatively with a theory developed by Doi and Edwards describing the strain-thinning behavior of semi-dilute rigid rod solutions.     

Characteristics of wave propagation and energy distributions in cylindrical elastic shells filled with fluid

The dispersion behaviour and energy distributions of free waves in thin walled cylindrical elastic shells filled with fluid are investigated. Dispersion curves are presented for a range of parameters and the behaviour of individual branches is explained. A non-dimensional equation which determines the distribution of vibrational energy between the shell wall and the contained fluid is derived and its variation with frequency and material parameters is studied.     

On-line FT-MIR/NIR process analysis

FT-IR spectrometers designed for laboratory operation are generally not suited for plant production areas where ambient temperatures often exceed 120° F and noise levels are extremely high. The Nicolet Pro-IR 5 process FT-IR spectrometer can operate in hostile environments over the spectral range from 10 000 to 250 wavenumbers. We have evaluated the performance of this system using a set of commercial detergent samples and a wide range of gas mixtures. The detergent samples were simultaneously analyzed for twelve components using a sophisticated partial least-squares statistical analysis software package. The concentrations ranged from 0.1 to over 50 wt.-%, with water being the major component. A comparison will be made between the NIR and MIR results using flow-through ATR (attenuated total reflectance) and transmission cells.