Direct probing of the fracture behavior for pseudo-free-standing polymeric ultra-thin films*

The understanding of fracture mechanics of free-standing ultra-thin polymeric films is crucial for modern technology that heavily relies on thin films, including the semiconductor industry and coating. Past decades have witnessed improved understanding of several physical properties of the ultra-thin film, however, their fracture behavior is rarely explored due to limited testing methods on hard-to-handle samples. In this work, we reported a new testing methodology that not only can directly measure the fracture energy of ultra-thin films floated on the water, but also visualize the local stress field during the deformation through the wrinkling pattern of the film. Using polystyrene as a model system, we demonstrated for the first time the existence of a critical molecular weight/thickness, below which the fracture energy increases consistently, and above which levels up. Later, this method was applied to other polymeric thin films for further demonstration of its broad applicability to both stiff and soft materials.