Insight into Polymer De-wetting: A Neutron Reflectivity Study of Three-Arm Polystyrene Stars in Polystyrene Thin films*

While polymeric coatings are ubiquitous, de-wetting remains a challenge. As both enthalpic and entropic contributions often affect the de-wetting process, small changes either compositional or in processing conditions are sufficient to impact the stability of thin films. We have recently shown that blending small amounts of three-arm polystyrene (PS) star polymers are sufficient to inhibit de-wetting of thin polystyrene thin films. The role of the three-arm star has been investigated using neutron reflectometry. We have followed the distribution of the three-arm PS stars in a thin film of d-PS as function of time as the temperature was raised above Tg of the PS. Films of d-PS/h-three-arm star PS were cast from toluene and the polymer profiles were determined as a function of time as the temperature was varied. The result show a clear migration of the three-arm stars to both interfaces, enhancing the number of chain ends at the interface. As the molecular weights of the star arm increases, it migrates slower to the interface.