Visualization and Quantification of the Microstructure Evolution of Isoprene Rubber during Uniaxial Stretching Using AFM Nanomechanical Mapping

Mapping and phase identification of the structure and mechanical property evolution of self-reinforced rubbers during deformation are difficult but important to reveal the self-reinforcement mechanism and fabricate advanced rubber products. Here, using the atomic force microscopy (AFM) nanomechanical mapping technique, and combined with Gaussian fitting of the modulus distribution profiles and recolored AFM modulus-mapping images, the structural evolution and mechanical response of deformed isoprene rubber (IR) has been identified quantitatively and visually. The results indicated that the entire rubber molecular segments were oriented during stretching, and the orientation was not uniform. The highly oriented shish-kebab structure along the stretching direction was directly observed in the crystalline-associated phase, which was responsible for the significant self-reinforcement. In addition, the crystallinity estimated by AFM observation was similar to the wide-angle X-ray diffraction (WAXD) results. Based on the AFM and WAXD results, a schematic model was proposed to illustrate the structural evolution and self-reinforcement mechanism of IR.