Effect of temperature-cycling on the morphology of polymeric thermotropic glazings for overheating protection applications

In this paper, the morphology of thermotropic systems with fixed domains (TSFD) was evaluated applying high resolution Atomic Force Microscopy (AFM) also upon heating and cooling. Furthermore nano-mechanical characteristics of the samples were determined by means of Force/Distance spectrometry. TSFD formulated with additive types exhibiting a short chain length displayed roughly spherical scattering particles with dimensions between 0.6 μm and 4 μm. By means of Force Distance spectroscopy stiffness values of 0.6 N/m and 7.8 N/m were determined for the scattering domains and the matrix, respectively. Upon heating, melting and deliquescence of the additive along with migration was ascertained. After cooling to ambient temperature the formation and growth of terrace-like additive domains on the surface was recorded. Additive types with long-chain molecules developed anisotropic scattering domains resembling distorted disks without predominating orientation. Diameters up to 50 μm and a thickness between 200 nm and 600 nm were ascertained. Determination of stiffness yielded values of 0.9 N/m and 13.1 N/m of the scattering domains and the matrix, respectively. Upon heating, swelling and deliquescence of the additive were detected. After cooling to ambient temperature a partial recovery of swelling was observed. Force-Distance spectroscopy yielded a 5 to 10 nm thick additive layer which coated wide areas of the surface after the heating cycle for all samples investigated.