The amount of silanol groups on the surface of glass or clay particles varies due to condensation reaction caused by heat treatment and the variation is measured by infrared spectroscopy. The variation affects the rheological properties of suspensions of these particles in polymer solutions as media. This effect is studied by applying sinusoidal deformation to the suspensions in a coaxial cylinder rheometer. Without heat treatment, the amplitude ratio of stress to strain exhibits a plateau, the second plateau, over a frequency range outside the plateau region of the medium. The height of the second plateau decreases in parallel to the decrease of the absorbance of 3700 cm-1 band characteristic of surface silanol groups. It is concluded that the surface silanol groups are primarily responsible to the aggregation of dispersed particles in the suspensions.
A method for measuring absolute values of normal stresses and stress optical coefficients can be developed by applying the scattered light interferometry for solid materials, the Mach-Zehnder interferometry, to viscoelastic fluids in flow and it can be shown that the difference between interferometric fringe orders for the polarized light in the flow direction and for that in the neutral direction must be equal to the birefringence fringe order. The results of measurements for a polyethylene melt, though not sufficiently accurate to allow evaluation of the normal stress and the stress optical coefficients, seemed compatible with the predictions of the proposed method.
The viscoelasticity of some glass-forming liquids was studied by means of the torsional braid analysis (TBA) which consists of measurements of storage and loss elastance in torsional oscillation on a glass braid saturated with a test liquid. The measurements were made along two different paths of temperature variation, slow cooling from room temperature to liquid nitrogen temperature and slow heating from the latter attained by rapid cooling. Tricresyl phosphate and dibutyl sebacate showed only one dispersion corresponding to glass transition and crystallization, respectively. Dimethyl phthalate and dioctyl phthalate showed one dispersion corresponding to crystallization in the slow cooling path, and two dispersions in the slow heating path. Diisooctyl azelate and di-2-ethylhexyl sebacate showed one dispersion corresponding to glass transition in the slow cooling path, and two dispersions in the slow heating path. The rather peculiar behavior observed for the last pair is probably attributed to a wide separation between optimum temperatures for crystal growth and nucleation.