title: Inducing uniform single-crystal like orientation in natural rubber with constrained uniaxial stretch.
abstract: The effect of flow on crystallization is commonly attributed to entropic reduction, which is caused by stretch and orientation of polymer chains but overlooks the role of flow on final-state free energy. With the aid of in situ synchrotron radiation wide-angle X-ray diffraction (WAXD) and a homemade constrained uniaxial tensile testing machine, polycrystals possessing single-crystal-like orientation rather than uniaxial orientation are found during the constrained stretch of natural rubber, whereas the c-axis and a-axis align in the stretch direction (SD) and constrained direction (CD), respectively. Molecular dynamics simulation shows that aligning the a-axis of crystal nuclei in CD leads to the lowest free energy increase and favors crystal nucleation. This indicates that the nomenclature of strain-induced crystallization may not fully account for the nature of flow-induced crystallization (FIC) as strain mainly emphasizes the entropic reduction of initial melt, whereas stress rather than strain plays the dominant role in crystal deformation. The current work not only contributes to a comprehensive understanding of the mechanism of flow-induced crystallization but also demonstrates the potential application of constrained uniaxial tensile stretch for the creation of functional materials containing polycrystals that possess single-crystal-like orientation.
authors.affiliation: National Synchrotron Radiation Lab & CAS Key Laboratory of Soft Matter Chemistry & Department of Polymer Science and Engineering, University of Science and Technology of China, Hefei, China. rychen@ustc.edu.cn lbli@ustc.edu.cn.
authors.forename: Weiming
authors.initials: W
authors.lastname: Zhou
authors.forename: Lingpu
authors.initials: L
authors.lastname: Meng
authors.forename: Jie
authors.initials: J
authors.lastname: Lu
authors.forename: Zhen
authors.initials: Z
authors.lastname: Wang
authors.forename: Wenhua
authors.initials: W
authors.lastname: Zhang
authors.forename: Ningdong
authors.initials: N
authors.lastname: Huang
authors.forename: Liang
authors.initials: L
authors.lastname: Chen
authors.forename: Liangbin
authors.initials: L
authors.lastname: Li
mesh_terms: D003460:Crystallization / Q000295:instrumentation; D004867:Equipment Design; D012408:Rubber / Q000737:chemistry*; D013314:Stress, Mechanical; D017356:Synchrotrons; D013718:Tensile Strength; D013816:Thermodynamics; D014961:X-Ray Diffraction / Q000295:instrumentation
chemical_list: D012408:Rubber