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A converging channel rheometer for the measurement of extensional viscosity

1990; Elsevier BV; Volume: 35; Issue: 2-3 Linguagem: Inglês

10.1016/0377-0257(90)85063-5

1873-2631

David F. James, G. M. Chandler, S.J. Armour,

Injection Molding Process and Properties

The development of an extensional rheometer for polymer solutions is described. The test section is a converging channel through which a test fluid is pushed at high Reynolds numbers, and several pressure drops along the channel are measured with flush-mounted transducers. The high Reynolds numbers ensure a core flow of purely extensional motion and the channel is shaped to produce a constant rate of extension. Analysis of the stress field shows that the pressure drop is equal to the normal stress difference τzz - τrr in the core, plus other terms which are calculated. The calculations are based on an analytical solution for inelastic power-law fluids, and the calculations were verified by finite element computations. Extensional viscosity measurements were made for a solution of a copolymer of PMMA in an organic solvent. The data show that extensional viscosity increases with extensional rate to about the 3/2 power and, at a fixed extensional rate, extensional viscosity increases roughly as the total fluid strain.