Connecting Morphology to Mechanical Response in Thin Block Copolymer Films

Understanding the mechanics of polymer thin films is critical to enhancing technologies including filtration membranes and multilayer packaging. While it is known that the mechanical response of thin glassy films is defined by polymer entanglements and molecular mobility, there remains a need to connect entanglement structure, mobility changes, and morphology to mechanical strength near surfaces. To investigate the connection, poly(styrene-b-2-vinylpyridine) is used as a model polymer where each block has similar properties and the processing methods for desired self-assembly are known. With this chosen system, we can offer direct insight into the structure-property relationships. Using a newly developed method, TUFF (Tensile tester for Ultrathin Freestanding Films), we measure the full uniaxial stress-strain response of freestanding poly(styrene-b-2-vinylpyridine) films below 100 nm in thickness. We characterize the nanoscale morphology, quantify the elastic modulus, maximum stress, and failure strain, and compare these results to homopolymer films of polystyrene. Our study connects the film morphology with the mechanical response and relates these behaviors to the fundamental polymer physics at the film’s interface.