Polymeric materials are lighter, softer, and processable than other materials such as metals and ceramics due to their low density and modulus, and are applied as components in automobiles, aircraft, and building materials. In various polymer material applications, there is a need to ensure long-term durability for safe and reliable use, and there is growing interest in the preparation of tough polymer materials and the elucidation of their fracture mechanisms. Against this background, our group have achieved toughening of latex film by introducing rotaxane crosslinker (RC) into microparticles (Fig.1a).[1-3] We found that the introduction of RCs improves the mechanical properties of polymer microparticles and is also important in strengthening the particle interface without additives. Furthermore, understanding the fracture behavior of latex films when various defects such as cracks and scratches are introduced is highly important as a strategy for tough polymeric materials. In this study, we investigated the effect of RC in microparticles on the fracture toughness of latex films.

The synthesized particle dispersion was dried on a glass substrate, and AFM observation confirmed that the width of the particles was about 100 nm and that they were highly monodisperse (CV~10 %) (Fig. 1b). Next, in the tear test, it was found that the elongation ratio and stress required to rupture the latex film with RC increased compared to that without RC (Fig. 1c). It was also observed that the cracks propagated randomly when RC was introduced. As a result, crack propagation was blunted, and toughness was improved compared to non-crosslinked. These results suggest that the introduction of RC into microparticles was a key factor for the formation of tough films.

<b>Fig.1</b> <b>(a)</b> Formation of latex films by the evaporation water from dispersion. <b>(b)</b> AFM image of RC-crosslinked microparticles. <b>(c) </b>Tear tests of notched latex films.

Fig.1 (a) Formation of latex films by the evaporation water from dispersion. (b) AFM image of RC-crosslinked microparticles. (c) Tear tests of notched latex films.

Toshikazu Takata

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