Transition Temperature Microscopy: Interpreting the morphology of an immiscible polymer blend

This note describes the application of nanoTA in the examination of a SAN/PC polyblend. The probe tip heats the sample locally at 25oC/sec while simultaneously monitoring the softening as the sample undergoes a glass transition Tg. Transition Temperature Microscopy is used to map mixing behavior and variations in phase composition originating at the nanoscale. Pure SAN and PC domains had lateral dimensions on the micron scale. Introduction Polymers are tailored to suit the most demanding applications on Earth, in space, and even in the human body. The engineering of material properties is accomplished primarily through the mixing of chemistries and the manipulation of structure. Sometimes in two identical compositions different morphology may arise. Factors influencing morphology may include processing conditions, molecular weight (MW) distribution, impurity, and lot to lot variation. In most applications, a reliable understanding and control over a given morphology accelerates research and can enhance output. High resolution morphology and structural organization define the overall bulk properties [1]. Transition Temperature Microscopy (TTM) is used to measure compositional variations in an amorphous polymer blend composed of polycarbonate (PC) and styrene-acrylonitrile (SAN). The Tg of SAN and PC was measured by DSC to be 115±6°C & 149±6°C respectively (figure 1). Thermal analysis methods will detect a single glass transition temperature in a binary blend if the two components are miscible. If the components are not miscible then there will be an individual Tg for each. In some non-miscible polymer blends the lower Tg is shifted higher in temperature than found in its pure state while the component with the higher Tg is lowered from its pure component Tg. In this Transition Temperature Microscopy: Interpreting the morphology of an immiscible polymer blend Authors Khoren Sahagian 1 and Harvey Bair 2 1 Anasys Instruments Corporation Santa Barbara, CA 2 Bell Laboratories (retired) NY, NY