A rheometer for generating uniaxial elongations in molten polymers has been modified to allow for the simultaneous measurement of stress and flow-induced birefringence. Tensile stress σ and birefringence Δn′ data in flows at constant strain rates up to 1 s−1 were collected on a polydisperse polystyrene melt at temperatures of 160 and 170 °C. From these data, the stress-optic rule was followed for stresses below roughly 1 MPa. For stresses less than 1 MPa, the stress-optic coefficient |C|=|Δn′|/σ was found to have a value of 4.8×10−9 Pa−1, which was independent of strain, strain rate, and temperature. At stress levels higher than 1 MPa, |C| decreased indicating a failure of the stress-optic rule. A criteria for failure of the stress-optic rule was formulated using simple arguments from network models and characteristic times suggested by the tube model. This criteria, which is based on the hypothesis that failure of the stress-optic rule is the result of significant chain stretching, was found to be consistent with the data reported in this study and with data from previous studies on polystyrene melts.

INFLUENCE OF LOW MOLECULAR WEIGHT POLYMERS ON THE RHEOLOGY OF BENTONITE SUSPENSIONSIn this communication we demonstrate how relatively low molecular weight synthetic polymers significantly alter the rheological properties of Bentonite/water suspensions depending upon the polymer dosage and/or degree of surface coverage on the clay particle. The behaviour of two types of nonionic polymers are reported; a series of nonylphenol poly(propylene oxide)-

A typical oil dispersion (OD) contains an oil, a powder (agrochemical) suspended in the oil as a carrier, an emulsifier capable of emulsifying the oil when diluted in water before spraying, a rheology modifier that can thicken and suspend the powder in the oil during storage, and optionally a suspension aid that can suspend the powder during spraying after the OD is diluted in water. Current commercially available rheology modifiers (thickeners) used or suggested for OD formulations have drawbacks. They are either difficult to handle (very dusty powder) or require heating or the use of a protonic solvent to activate thickening. In addition, their thickening property is sensitive to ionic surfactants such as Ca-DDBS and temperature change. In this paper, a new type of oil thickener, a polymer, without the drawbacks of current oil thickeners, is introduced. It is believed that the new type of oil thickener uses a chain entanglement or excluded volume-thickening mechanism rather than the associative- or solidification-thickening mechanism employed by the current thickeners. A few stable OD prototypes containing powder pesticides (5 %–48 %), emulsifiers (6 % or less), and this unique polymeric rheology modifier (3 % or less) in oils (soy methyl ester or Aromatic 200) are presented. A correlation between OD stability and the loss-factor frequency dependence (G″/G′, the ratio of loss modulus to storage modulus) is established. In particular, when G″/G′ is less than 1, the OD is stable. When G″/G′ is greater than 1, the OD is unstable and the solid particles tend to settle to the bottom.