Diffusion effects on the interfacial tension of immiscible polymer blends |
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Authors: | Stefano Guido Marino Simeone Marco Villone |
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Institution: | (1) Laboratori “Giovanni Astarita” Dipartimento di Ingegneria chimica Università degli Studi di Napoli “Federico II” P. le V. Tecchio, 80 I-80125 Naples, Italy, IT |
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Abstract: | Most methods of measuring the interfacial tension between two immiscible polymers are based on the analysis of the shape
that a drop of one polymer immersed in the other one exhibits under the action of flow or gravity. In such a situation, the
small, yet nonzero mutual solubility between the two polymers acts toward mass transfer between the drop and the surrounding
fluid. In this work, diffusion effects on the interfacial tension of the pair polyisobutylene/polydimethylsiloxane have been
investigated by drop deformation under shear flow. When the drop was made of polyisobutylene, drop size decreased with time
due to diffusion. Drop shrinkage was associated with a significant increase in interfacial tension, until an apparent plateau
value was reached. The effect was attributed to a selective migration of molecular weights, which would act to enrich the
drop with higher molar mass material. To support such an interpretation, drop viscosity was evaluated by drop shape analysis
and it was actually found to increase with time. In some cases, the ratio between drop and continuous phase viscosity became
higher than the critical value for drop breakup in shear flow. Upon inverting the phases (i.e., when the drop was made of
polydimethylsiloxane), no significant transient effects were observed. In the light of these results, the problem of what
are the correct values of interfacial tension and viscosity ratio for a polymer blend of a certain composition will also be
discussed.
Received: 25 January 1999 Accepted: 24 May 1999 |
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Keywords: | Interfacial tension Immiscible polymer blends Drop deformation Shear flow Diffusion |
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