How does morphology impact the mechanical properties of ultrathin block copolymer films?

Thin films are critical to enhancing technologies such as packaging, membranes, and flexible electronics. However, below 100 nm in thickness, polymer chain behavior differs from the bulk. Here, we discuss a recent study that focuses on elucidating the role of entanglements and microstructural domains in determining mechanical strength and ductility for ultrathin films. We use poly(styrene-b-2-vinylpyridine) as a model system, where the block copolymer domains have similar properties. The morphology of the films is altered through solvent vapor annealing and measured using The Uniaxial Tensile Tester for UltraThin films (TUTTUT). These results show how relative positioning of phase-separated blocks within a thin film can significantly alter a film's mechanical response. For a freestanding thin film measurement, ordered lamellar morphology films withstand higher stresses than disordered films. Placing these films on a water surface during uniaxial extension caused local domain plasticization, increasing failure strains in comparison to freestanding films. Through this research, we are expanding the knowledge of how molecular entanglements and mobility influence the mechanical response of thin glassy polymer films and developing design principles for creating strong thin materials.