Probing the Impact of Free Surfaces on the Glass Transition and Physical Aging in Ultrathin Polymer Films

摘要

As technological applications are made smaller and smaller, the role of free surfaces on the properties of the material become increasingly important. Nanoscale materials, used in a variety of applications from microelectronics and nanolithography to gas separation membranes, exhibit material properties that can be strongly perturbed from their bulk values because of the increased surface-to-volume ratio of these materials. One of the least well-understood effects is how the presence of a free surface imparts excess mobility to the near surface region and is then propagated deeper into the material. To elucidate the underlying fundamental mechanisms of how this enhanced mobility near a free surface affects the glass transition of polymeric materials over length scales of tens of nanometers, we have performed glass transition temperature (Tg) and physical aging measurements of ultrathin free-standing polystyrene (PS) films.