Stress-Structure Relationship of the Reversible Associating Polymer Network under Start-up Shear Flow
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ARTICLE
POLYMER SCIENCE
https://doi.org/10.1007/s10118-020-2487-6 Chinese J. Polym. Sci.
Stress-Structure Relationship of the Reversible Associating Polymer Network under Start-up Shear Flow Ai-Qing Liua,b, Li-Jun Liub*, Wen-Sheng Xub*, Xiao-Lei Xub*, Ji-Zhong Chenb*, and Li-Jia Anb,c a College of Chemistry, Jilin University, Changchun 130012, China b State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, China c University of Science and Technology of China, Hefei 230026, China
Abstract We adopt Langevin dynamics to explore the stress-structure relationship of telechelic reversible associating polymer gel during startup shear flow, with shear strengths varying from Wi = 12.6 to Wi = 12640. At weak shear flow Wi = 12.6, the shear stress proportionally increases with shear strain at short times, followed by a strain hardening behavior and then passes through a maximum (σmax, γmax) and finally decreases until it reaches the steady state. During the evolution of stress, the gel network is only slightly broken and essentially maintains its framework, and the strain hardening behavior originates from the excessive stretching of chains. On the other hand, the stress-strain curve at intermediate shear flow Wi = 505.6 shows two differences from that at Wi = 12.6, namely, the absence of strain hardening and a dramatic increase of stress at large strains, which is caused by the rupture of gel network at small strains and the network recovery at large strains, respectively. Finally, at very strong shear flow Wi = 6319.7, the gel network is immediately broken by shear flow and the stress-strain curve exhibits similar behaviors to those of classical polymeric liquids. Keywords Associating polymer; Start-up shear; Stress-structure relationship Citation: Liu, A. Q.; Liu, L. J.; Xu, W. S.; Xu, X. L.; Chen, J. Z.; An, L. J. Stress-structure relationship of the reversible associating polymer network under start-up shear flow. Chinese J. Polym. Sci. https://doi.org/10.1007/s10118-020-2487-6
INTRODUCTION Reversible associating network gels, also known as physical gels, have attracted extensive attention in recent years. A transient gel network is composed of crosslinks that are formed by noncovalent bonds, such as hydrogen bonding, ionic bonds, metal complexation,[1] and π-π stacking.[2−7] Because of their unique abilities such as the outstanding processing and recycling resulting from the nature of reversible cross-linking, physical gels exhibit superior properties over traditional polymer materials, with numerous applications in fields such as biological and industrial technology and engineering artificial tissue. For example, the associated polymeric networks can be used in shape memory,[8−12] drug release,[13] response stimulation[14−17] and self-healing materials.[18−24] In addition, many researchers also focused on polymer hydrogel designs that can absorb water or biological fluids to address medical needs.[25−28] A polymer
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