Variable-Temperature Atomic Force Microscopy: Applications to Studies of Semicrystalline Polymers

摘要

Most AFM studies to date have been conducted at ambient temperature. This presents a substantial limitation when information about the thermal behavior of the sample surface is desirable. For example, performance of plastics is strongly temperature-dependent since they can exhibit complex thermal behavior marked by multiple thermal transitions, such as melting, crystallization, recrystallization, phase separation, as well as glass and sub-glass transitions. Experiments illustrating in situ AFM monitoring of polymer crystallization show the unique capability of this technique for measuring the growth of individual crystalline lamellae [1]. The polymers chosen for the above-cited studies undergo crystallization at room temperature; yet many polymers undergo phase transitions at elevated temperatures. To study these polymers, early experiments were conducted on samples heated externally for different time periods and then placed on the AFM and examined at room temperature [2]. This approach was very laborious since it required high precision in locating the same spot on the sample surface using special landmarks. In addition, this procedure is not always acceptable because of the changes that can occur in the polymer structure on cooling to room temperature. Therefore, in situ AFM studies at elevated temperatures are invaluable for analysis of polymers. The present work addresses a number of important issues relevant to AFM studies at elevated temperatures. Several examples of AFM studies on polymer materials at temperatures up to 233 deg C are provided.