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Direct Observations of the Structure of a Main-Chain Thermotropic Liquid-Crystalline Homopolyester by Scanning Tunneling Microscopy

The structure of a main-chain thermotropic liquid-crystalline homopolyester, poly [(phenylsulfonyl)- p-phenylene 1,10-decamethylene-bis(4-oxybenzoate)] (PSHQ10), having a melting point of approximately 110°C and the nematic-isotropic transition temperature of approximately 175°C, was investigated using scanning tunneling microscopy (STM). For taking STM images we employed two samples of PSHQ10: sample A was an as-cast film which received no thermal treatment and sample B was an as-cast film which was thermally treated above the melting point. The STM images show that (i) sample A has a molecular arrangement which is in good agreement with the crystallographic data obtained in a wide-angle X-ray diffraction study, and (ii) sample B has both crystal-like and bundle regions. The STM images of sample B are interpreted as representing a structure which, according to results obtained by Han et al. [Macromolecules 26 (1993) 3176], is a high-temperature melting crystal formed via recrystallization during annealing.