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  • 1
    Electronic Resource
    Electronic Resource
    Comparison of optical and mechanical measurements of second normal stress difference relaxation following step strain (1995)
    Springer
    Rheologica acta 34 (1995), S. 221-234 
    Details
    ISSN: 1435-1528
    Keywords: Second normal stress difference ; birefringence ; tube model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Relaxation of the second normal stress difference (N 2) following step strain of a concentrated monodisperse polystyrene solution has been studied using mechanical and optical rheometry. Measurements of normal thrust in a parallel plate geometry are corrected for strain inhomogeneity and combined with independent measurements of the first normal stress difference (N 1) to determine N 2. Optical experiments were performed using a novel configuration where flow birefringence data collected using multiple light paths within the shear plane are combined with the stress-optical law to determine all three independent stress components for shearing deformations. This technique eliminates end effects, and provides an opportunity to oversample the stress tensor and develop consistency checks of experimental data. N 2 is found to be nonzero at all accessible times, and relaxes in roughly constant proportion to N 1. This reflects nonaffine distribution of chain segments, even well within the regime of chain retraction at short times. Data collected with the two techniques are reasonably consistent with each other, and with results of previous studies, generally lying between the predictions of the Doi-Edwards model with and without the independent alignment approximation. The normal stress ratio −N 2/N 1 shows pronounced strain thinning in the nonlinear regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00396013
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  • 2
    Electronic Resource
    Electronic Resource
    Exponential shear flow of branched polymer melts (2000)
    Springer
    Rheologica acta 39 (2000), S. 71-79 
    Details
    ISSN: 1435-1528
    Keywords: Key words Exponential shear ; Polymer melt ; Flow classification ; Strong flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract   The behavior of a low-density polyethylene melt in exponential shear strain histories is examined and compared to its behavior in constant rate planar elongation. A new set of shear stress and first normal stress difference data in exponential shear are presented and used in several different material functions that have been previously proposed. Viscosities composed of principal stress differences for the two flows showed no correspondence suggesting that, contrary to previous assertions, exponential shear and constant rate planar elongation flows are fundamentally different. It is further suggested that the presence of vorticity makes exponential shear a weak, rather than strong, flow.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970050008
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  • 3
    Electronic Resource
    Electronic Resource
    Equibiaxial extensional flow of polymer melts via lubricated squeezing flow. I. Experimental analysis (2000)
    Springer
    Rheologica acta 39 (2000), S. 444-451 
    Details
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract The technique of lubricated squeezing flow is evaluated using experiments in both constant strain rate and constant stress flows of two low-density polyethylene melts. Experimental parameters that include the lubricant viscosity and sample aspect ratio are systematically varied to examine their effect on the viability of the technique in the linear viscoelastic regime by comparing measured quantities to those predicted by finite linear viscoelastic theory. An evaluation is also made by comparing viscosities measured using the lubricated squeezing flow technique and Meissner's rotating clamp (MAD) rheometer in the non-linear regime. In both cases, deviations between the expected and measured viscosities were observed, indicating that the technique is not applicable to large strains for constant strain rate and constant stress flows. It is suggested that this limit is the result of lubricant thinning.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970000106
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  • 4
    Electronic Resource
    Electronic Resource
    Equibiaxial extensional flow of polymer melts via lubricated squeezing flow. II. Flow modeling (2000)
    Springer
    Rheologica acta 39 (2000), S. 574-582 
    Details
    ISSN: 1435-1528
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract A model for lubricated squeezing flow of a viscoelastic fluid is developed in order to study the viability of this flow as a rheological technique for generating equibiaxial extensional deformations in polymer melts. In this simple flow model, the melt, described by an upper-convected Maxwell fluid, is squeezed between thin films of a Newtonian fluid. Comparisons of the model predictions for constant strain rate and constant stress flows are made with experimental results presented in the first paper. Predictions from the model are able to describe the effects of lubricant viscosity and experimental configuration and indicate the technique fails for these flows at Hencky strains of approximately one. The cause for this failure is lubricant thinning, which leads to significant errors in both the measured stress difference and the strain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s003970000107
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Transport analysis of diffusion-induced bubble growth and collapse in viscous liquids (1997)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 43 (1997), S. 2948-2959 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Transport models of diffusion-induced bubble growth and collapse in viscous liquids are developed and evaluated. A rigorous model for these important phenomena is formulated taking into account convective and diffusive mass transport, surface tension, and viscous and inertial effects. Predictions for bubble growth dynamics demonstrate the importance of viscous effects in the liquid surrounding the bubble for a wide range of conditions having relevance to polymer processing operations. It is also shown how previous models employing various approximations can be derived from the rigorous model by using different mathematical methods and dimensional analysis. Predicted bubble growth dynamics from the rigorous and approximate models are compared to establish the ranges of validity for two commonly used approximations. These comparisons indicate that models using a thin boundary-layer approximation have a rather limited range of applicability. A new approximate model, based on a previously published result, gives reasonably accurate bubble growth rate predictions with a significant reduction in computational effort.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690431108
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    Paper (German National Licenses)
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