Letter | Published:

The extensional flow capillary as a new method for extensional viscosity measurement

Abstract

THE behaviour of non-newtonian fluids in extensional flow is of both theoretical and practical importance. However, because of the difficulty of imposing a purely extensional deformation on a fluid material, very few experimental measurements of extensional viscosity have been obtained in well defined kinematic conditions. All of the experimental techniques currently available which utilise constant extension rate kinematics involve the application of a tensile stress to a cylindrical sample, and thus require the assumption of uniform deformation of material which is bounded by a free surface. These techniques are applicable only for very high viscosity materials (> 105 P), and are difficult to use in the study of materials whose resistance to extensional deformation is ‘tension thinning’ because of a tendency of the sample to neck and fail. We describe here an extensional flow capillary rheometer which we have evaluated for the measurement of extensional flow properties of a wide variety of materials over a broad range of extension rates. Recent discussion1 of a ‘speculative rheometer’ of apparently similar design emphasises the value of such a device.

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References

  1. 1

    Bull. Br. Soc. Rheol. 20 (2), 17–18 (1977).

  2. 2

    Meissner, J. Trans. Soc. Rheol. 16, 405 (1972).

  3. 3

    Everage, A. E., Jr & Ballman, R. L. J. appl. Polym. Sci. 21, 841 (1977).

  4. 4

    Everage, A. E., Jr & Ballman, R. L. J. appl. Polym. Sci. 20, 1137 (1976).

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