Abstract
The primary normal-stress difference has been measured for concentrated solutions of rodlike and flexible chain polyamides. The solutions studied here consist of poly-p-phenyleneterephthalamide (PPT) which is believed to be rodlike in 100% H2SO4 and the flexible chain polyamide, polyhexamethylene adipamide (nylon 6.6), which is also dissolved in 100% sulfuric acid. For the PPT solutions the primary normal-stress difference coefficient in the limit of zero shear rate (ψ 1(0)) is observed to be proportional toM 12.9 whereM w is the weight average molecular weight. For concentrated solutions of nylon 6.6,ψ 1(0) is found to be proportional toM 7.6 which is in reasonable agreement with values reported for other flexible chain polymers. These data point out that there are some interesting differences in the primary normal stress differences for rodlike and flexible chain polymers and at the same time provide support of the recent theoretical predictions ofDoi andEdwards for concentrated solutions of entangled rodlike molecules.
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