Liu Han, Huang Guangsu, Zeng Jian, Xu Lili, Fu Xuan, Wu Siduo, Zheng Jing, Wu Jinrong
College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University , Chengdu 610065, China.
J Phys Chem B. 2015 Sep 3;119(35):11887-92. doi: 10.1021/acs.jpcb.5b05113. Epub 2015 Aug 13.
Potential competition between fringed-micelle nucleation (N1) and folded-chain nucleation (N2) widely exists in strain-induced crystallization (SIC). However, during uniaxial deformation, no in situ observational evidence of nucleation transition from N2 to N1 in SIC of natural rubber (NR) has been reported yet. In this work, self-seeding provides an effective way for this observation. By the introduction of residual TIC (temperature-induced crystallization)-melting crystallites into pure NR system, in situ synchronic WAXD revealed the formation of low-oriented crystal in the initial deformation stage, which gradually evolves into highly oriented crystal at last. The low-oriented crystal is related to secondary folded-chain nucleation (N2) on the surface of residual TIC-melting crystallites (self-seeding), while newly formed highly oriented crystal is associated with N1. For the first time, the concept of "self-seeding" is innovatively applied to SIC process so that NR exhibits clear nucleation transition phenomenon. Further, theoretical computation of nucleation barrier in the special NR system well reflects that self-seeding has the role of both increasing critical strain of nucleation transition and decreasing onset strain of SIC, thus providing conditions for the observation.
在应变诱导结晶（SIC）过程中，缨状胶束成核（N1）和折叠链成核（N2）之间的潜在竞争广泛存在。然而，在单轴变形过程中，尚未有关于天然橡胶（NR）的SIC中从N2到N1的成核转变的原位观测证据报道。在这项工作中，自晶种法为这种观测提供了一种有效方法。通过将残余的温度诱导结晶（TIC）-熔融微晶引入纯NR体系，原位同步广角X射线衍射（WAXD）揭示了在初始变形阶段形成了低取向晶体，该晶体最终逐渐演变成高取向晶体。低取向晶体与残余TIC-熔融微晶表面的二次折叠链成核（N2）（自晶种）有关，而新形成的高取向晶体与N1有关。首次将“自晶种”概念创新性地应用于SIC过程，使得NR呈现出清晰的成核转变现象。此外，对特殊NR体系中成核势垒的理论计算很好地反映出，自晶种具有增加成核转变临界应变和降低SIC起始应变的作用，从而为观测提供了条件。
