Melt Rheology of Lower Critical Solution Temperature Polybutadiene/Polyisoprene Blends

Published

December 1, 2000

Author(s)

H Jeon, A Nakatani, Charles C. Han, R H. Colby

Abstract

The viscoelastic properties of a near critical polybutadiene(PB)/polyisoprene(PI) blends with an entangled structure and a dynamic symmetry ({Δ}Tg {approximately equal to} 27 K and {Δ}T∞ {approximately equal to} 39 K) were investigated in oscillatory shear above and below the lower critical solution temperature (LCST), where Tg and T∞ are the glass transition and Vogel temperatures, respectively. The dynamic loss modulus of a near critical PB/PI blend above and below the LCST is well described by means of a log additive mixing rule. A single master curve in the loss modulus of the critical blend exhibiting William-Landel-Ferry behavior was obtained below the LCST by using the time temperature superposition (TTS) principle. However, the storage modulus and loss tangent above the LCST deviate from both the TTS principle and the log additive mixing rule.The phase separated PB/PI blends within the linear viscoelastic regime display higher than expected values of storage modulus at low frequencies. This is due to the interfacial tension between the two phases of the blend. In contrast, the loss modulus of the blends at low and high frequencies is not affected by the interfacial tension. We also found a discontinuity in the temperature dependence of the dynamic storage modulus. The discontinuity is related to the macrophase separation temperature of the blend, and it is affected by oscillatory shear. In addition, the macrophase separation temperature (Tc) determined from the storage modulus was obtained as a function of frequency, and it is evident that an extrapolation to ω = 0 provides a good agreement with Tc = (61.5 ± 0.5) degrees C measured under quiescent conditions by optical microscopy.

Citation

Macromolecules

Volume

33

Issue

No. 26

Pub Type

Journals

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Keywords

elastic energy, interfacial tension, melt rheology, polybutadiene, polyisoprene

Citation

Jeon, H. , Nakatani, A. , Han, C. and Colby, R. (2000), Melt Rheology of Lower Critical Solution Temperature Polybutadiene/Polyisoprene Blends, Macromolecules, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=851617 (Accessed November 8, 2024)