Liu Shuang, Cao Xiao, Huang Chongwen, Weiss R A, Zhang Zhijie, Chen Quan
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, 130022 Changchun, China.
University of Science and Technology of China, 230026 Hefei, China.
ACS Macro Lett. 2021 Apr 20;10(4):503-509. doi: 10.1021/acsmacrolett.1c00018. Epub 2021 Apr 12.
This study examines the brittle-to-ductile transition of sulfonated polystyrene ionomers (SPS) with different counterions. The polystyrene precursor was unentangled and had two ionic groups per chain on average. Thus, its terminal relaxation time was comparable to the lifetime of the associating ionic groups. Three types of ionomer samples were used to tune the association lifetime: (1) fully neutralized SPS with different alkali-metal counterions, (2) fully neutralized SPS with mixed sodium and cesium counterions, and (3) partially neutralized SPS with sodium or cesium counterions. For all three systems, the brittle-to-ductile transition could be represented by a diagram of two Weissenberg numbers, and , defined with respect to the terminal and Rouse relaxation times, respectively. A flowable region existed at sufficiently low , independent of . At higher , a brittle-to-ductile transition of the ionomer melt occurred above a critical value of . To achieve ductility during the application of rapid elongational flow, the Rouse-type motions should be sufficiently slow relative to the rate of ion-dissociation, so that the strain-induced breakup of the ionic cross-links would not cause very strong chain retraction that may further lead to the macroscopic fracture.
本研究考察了具有不同抗衡离子的磺化聚苯乙烯离聚物（SPS）的脆韧转变。聚苯乙烯前驱体未缠结，平均每条链有两个离子基团。因此，其末端弛豫时间与缔合离子基团的寿命相当。使用三种类型的离聚物样品来调节缔合寿命：（1）具有不同碱金属抗衡离子的完全中和的SPS，（2）具有混合钠和铯抗衡离子的完全中和的SPS，以及（3）具有钠或铯抗衡离子的部分中和的SPS。对于所有这三个体系，脆韧转变可用分别相对于末端弛豫时间和Rouse弛豫时间定义的两个魏森贝格数的图来表示。在足够低的 时存在一个可流动区域，与 无关。在较高的 时，离聚物熔体在 的临界值以上发生脆韧转变。为了在快速拉伸流动应用过程中实现延展性，Rouse型运动相对于离子解离速率应足够慢，以使应变诱导的离子交联破裂不会导致非常强烈的链回缩，而这可能进一步导致宏观断裂。
