Mechanical Deformation Behavior of Polymer Blend Thin Films

Examining the mechanical properties of polymer thin films is crucial for high-performance applications such as displays, coatings, sensors, and thermal management. It is important to design thin film microstructures that excel in high-demand situations without compromising mechanical integrity. Here, a polymer blend of polystyrene (PS) and polyisoprene (PI) is used as a model to explore microscale deformation behavior under uniaxial mechanical testing. Six thin film compositions ranging from pure PS to a 4.5:5.5 ratio of PS to PI are fabricated. The thin films are deformed under compression, tension, and cyclic loadings, while monitoring the behavior utilizing a micromechanical stage and optical microscopy. To calculate the plane strain modulus, a strain-induced elastic buckling instability technique is employed. The results show that as the PI concentration increases, the plane strain modulus of the films decreases while the fracture strain increases. For the 4.5:5.5 ratio of PS to PI with a continuous rubbery PI phase, the thin films show major recoverable mechanical performance. This behavior is attributed to the mechanical strength of glassy PS combined with the strain energy absorption capability of rubbery PI, enabling elastic recovery. These fundamental observations provide valuable insights for designing mechanically resilient thin films for coatings and flexible devices.