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Updated: Jul 25, 2025

Studying Large Amplitude Oscillatory Shear Response of Soft Materials
Published on: April 25, 2019
Distinguishing between Linear and Star Polystyrenes with Unentangled Arms by Dynamic Oscillatory Shear Tests
Hyeong Yong Song1, Seung Joon Park2, Kyu Hyun1
1School of Chemical Engineering, Pusan National University, Busan 46241, Republic of Korea.
Abstract:
Linear and nonlinear viscoelastic properties of star polystyrene (PS) melts with unentangled arms were measured by using small-amplitude and medium-amplitude oscillatory shear (SAOS and MAOS) tests. For comparison purposes, such tests were also conducted on entangled linear and star PS melts. Interestingly, the linear viscoelastic properties of unentangled star PS were quantitatively described using the Lihktman-McLeish model for entangled linear chains, indicating that unentangled stars were indistinguishable from linear chains by using relaxation spectra. By contrast, the relative intrinsic nonlinearity (Q0), one of the MAOS material functions, exhibited a difference between unentangled star and linear PS. When the maximum Q0 value (Q0,max) was plotted against the entanglement number of span molecules (Zs), unentangled star PS exhibited larger Q0,max values than linear PS, which was quantitatively predicted via the multimode K-BKZ model. Therefore, in the unentangled regime, star PS was concluded to be characterized by intrinsically higher relative nonlinearity than linear PS.
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