High-Shear-Rate Behavior of Radial Hydrogenated Styrene−Isoprene and Block Ethylene−Propylene Copolymer Solutions

Abstract

Using a capillary viscometry technique, the high-shear-rate behavior of two polymer additives (an ethylene−propylene block copolymer and a radial hydrogenated styrene−isoprene copolymer) in a hydrocarbon-based oil solution has been investigated. At mass concentrations of up to 2.0% for the styrene−isoprene copolymer and 1.5% for the ethylene−propylene additive, the viscosity was measured over a range of shear rates from 104 to 106 s-1. To correct for the effects of viscous heating and pressure changes, a numerical correction procedure is used which reduces the experimental results to viscosity data at a common reference temperature and pressure for comparison. Over the range of shear rates examined, the styrene−isoprene solutions exhibited typical shear-thinning behavior, becoming more dramatic at higher polymer concentrations. In addition to shear thinning at the higher shear rates, a shear-thickening region was observed in the more concentrated ethylene−propylene solutions. As the polymer concentration increased, the degree of shear thickening was shown to be more severe and the critical region was observed at lower shear rates.

An experimental investigation into the dimension-sensitive viscosity of polymer containing lubricant oils in microchannels

“…1(b) and 2(b) it is apparent that as channel height is increased the results for the 1.0% solutions are converging towards the bulk viscosity (measured with a 105 lm channel) over the entire range of shear rates. The slight shear thinning behavior as well as the magnitude of the viscosity observed in the 105 lm channels is consistent with the behavior reported for identical polymer solutions measured using a traditional capillary viscometer in an earlier study [13], suggesting that indeed these results do represent the true bulk viscosity.…”

“…The latter of these two have been minimized here by design techniques adapted from capillary viscometers, such as the low height to length ratio (on the order of 1:1000 in this case). The influence of in-channel viscosity gradients, caused by a coupling of viscous heat generation and pressure dependent viscosity, on the results obtained from pressure-driven shear viscometer are well documented, especially for the capillary tube case [13,[22][23][24][25].…”

“…To examine this effect for the slit microchannel viscometer used in this work, a numerical correction procedure presented in an earlier paper [13] was extended to the slit flow geometry. The correction procedure is based on a numerical solution of the equations for continuity, momentum and energy, coupled with experimental results and an assumed viscosity transport relation to predict the in-channel viscosity profile and to reduce the data to an apparent viscosity at a common reference temperature and pressure.…”

“…These polymers were selected for this study due to their use as practical significance as rheology modifiers in automotive engine oils. In a previous study [13] the high shear rate (10 4 -10 6 1/s) behavior of both these polymers over a similar range of concentrations was examined. In that study solutions of the styrene-isoprene copolymer exhibited typical shear thinning behavior over the range of shear rates, while the ethylene-propylene copolymer showed much more complicated behavior including a region of shear thickening.…”

“…The styrene-isoprene copolymer examined here is a random copolymer of the star type that is comprised of numerous branches extending from a central point. The rheology of block styrene-isoprene copolymers have been investigated by a number of authors [14,15], however a literature review shows that other than [13] little work has been done in investigating the radial (star) form of this polymer type. The ethylene-propylene copolymer of interest to this study is comprised of approximately 60% ethylene units concentrated in the middle of the chain (the polymer is manufactured in a tubular reactor which allow the position of the ethylene units along the chain to be controlled).…”