Distinguishing between Linear and Star Polystyrenes with Unentangled Arms by Dynamic Oscillatory Shear Tests

Hyeong Yong Song; Seung Joon Park; Kyu Hyun

doi:10.1021/acsmacrolett.3c00112

Distinguishing between Linear and Star Polystyrenes with Unentangled Arms by Dynamic Oscillatory Shear Tests

ACS Macro Lett. 2023 Jul 18;12(7):968-973. doi: 10.1021/acsmacrolett.3c00112. Epub 2023 Jun 30.

Authors

Hyeong Yong Song¹, Seung Joon Park², Kyu Hyun¹

Affiliations

¹ School of Chemical Engineering, Pusan National University, Busan 46241, Republic of Korea.
² Department of Chemical Engineering and Biotechnology, Tech University of Korea, Siheung-Si, Gyeonggi-Do 15073, Republic of Korea.

PMID: 37389980
DOI: 10.1021/acsmacrolett.3c00112

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 (Q_0,max) was plotted against the entanglement number of span molecules (Z_s), unentangled star PS exhibited larger Q_0,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.