Detecting structural orientation in isoprene rubber/multiwall carbon nanotube nanocomposites at different scales during uniaxial deformation

Enhanced strain‐induced crystallization (SIC) behavior in isoprene rubber/multiwall carbon nanotube (IR/MWCNT) nanocomposites was analyzed in terms of structural orientation during uniaxial deformation. In situ synchrotron wide‐angle X‐ray diffraction and small‐angle X‐ray scattering (SAXS) reveal the molecular orientation in IR/MWCNT composites at different scales. The inclusion of MWCNTs leads to a decrease in the molecular orientation at small strain due to the promotion of SIC. Meanwhile, the presence of MWCNTs induces a large‐scale orientation within the vulcanized rubber network based on SAXS results. Considering the heterogeneous nature of the vulcanized network, the nucleation process during SIC is discussed from the viewpoint of thermodynamics. The oriented large‐scale structure in IR/MWCNT composites is composed of local rubber chains stretched up MWCNTs, from which the additional nuclei are induced. By forming a bound rubber layer around MWCNTs through attractive interactions, MWCNTs can amplify the local strain of rubber segments and form a highly oriented large‐scale structure, but without altering the overall molecular orientation level. The evolution of detailed structural orientation in MWCNT‐filled rubber composites during deformation is revealed for the first time. © 2017 Society of Chemical Industry Structural orientation of multiwall carbon nanotube (MWCNT)‐filled isoprene rubber at different scales is investigated using in situ synchrotron wide‐angle X‐ray diffraction and small‐angle X‐ray scattering experiments. During uniaxial deformation, MWCNTs induce a large‐scale orientation at small strain without altering the overall amorphous orientation degree of the rubber matrices in IR composites. The highly orientated structure in rubber matrices originates from MWCNTs and the bound rubber layer formed in their vicinity through attractive interactions. A thermodynamic analysis of strain‐induced crystallization behavior reveals that MWCNTs could enlarge the effective elongation ratio of the local chains and lower the nucleation barrier of rubber molecules. Considering the non‐uniformity in the vulcanized network, the evolution of detailed structural orientation at different scales in the composites is revealed.