Surface chemical composition and conformation of liquid crystalline polymers studied with ToF‐SIMS and XPS

Abstract

In this work, we examined the effects of the liquid crystalline ordering on the surfaces of thermotropic fluorocarbon-hydrocarbon polymers (FmHn, with m = 8; n = 8, 10) by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with principal component analysis (PCA). XPS results showed that the liquid crystal surfaces of the polymers were enriched with hydrocarbon segments. PCA of ToF-SIMS data further showed that reversible structural changes between the amorphous and ordered states of the polymers occurred. As these polymers ordered at room temperature, their surfaces were transformed from the amorphous state with fluorocarbon-segment enrichment to the fully ordered liquid crystal states with hydrocarbon-segment enrichment. All these results suggested that the molecular orientation controlled the surface composition of the liquid crystalline polymers notwithstanding the surface energy. The axial alignment of the rigid fluorocarbon mesogens anchored the flexible hydrocarbon segments at the surface.

Effects of pretreatment temperature on the analysis of size‐fractionated aerosol particles using ToF‐SIMS

“…All these studies have shown that ToF‐SIMS is a very suitable technique for investigating the surface chemical compositions of aerosol particles because it possesses several advantages: (a) Both inorganic and organic components can be analyzed simultaneously; (b) single particle analysis is possible using ToF‐SIMS imaging when the particles are bigger than a few hundred nanometers; and (c) not only the surface composition of aerosol particles but also the distribution of chemical composition along the depth of aerosol particles can be obtained using ToF‐SIMS. As ToF‐SIMS spectra contain massive amount of data, multivariate method such as principal component analysis (PCA) has been often used to facilitate data interpretation …”

“…As ToF-SIMS spectra contain massive amount of data, multivariate method such as principal component analysis (PCA) has been often used to facilitate data interpretation. 10,[27][28][29] One of the critical issues in the analyses of aerosol particles using ToF-SIMS and other techniques mentioned above is the potential evaporation of volatile and semivolatile organic compounds (VOCs and SVOCs) under ultrahigh vacuum conditions. VOCs usually refer to chemicals with boiling points < 240 C at standard atmospheric pressure, while SVOCs exhibit boiling point from 240 C to 400 C. Both VOCs and SVOCs have been confirmed to partition into aerosol particles.…”

The surface chemical composition and structure of a fluorocarbon–hydrocarbon block copolymer

“…The fluorinated components tend to migrate to the surface of amorphous polymers due to their low surface energies, with the one exception that they can migrate to the bulk when they are incorporated in a crystallizable backbone . Applications of time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) to surface studies of amorphous, semi‐crystalline and liquid crystal polymers are well documented . In our previous study , we applied ToF‐SIMS to study the surface compositions of [‐(CF 2 ) n ‐(CH 2 ) m ‐] N polymers with n = 8, 10 and m = 8.…”

“…Applications of time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) to surface studies of amorphous, semi‐crystalline and liquid crystal polymers are well documented . In our previous study , we applied ToF‐SIMS to study the surface compositions of [‐(CF 2 ) n ‐(CH 2 ) m ‐] N polymers with n = 8, 10 and m = 8. The results showed that at room temperature, the surfaces of these polymers changed from fluorocarbon rich to hydrocarbon rich as they crystallized .…”

“…In our previous study , we applied ToF‐SIMS to study the surface compositions of [‐(CF 2 ) n ‐(CH 2 ) m ‐] N polymers with n = 8, 10 and m = 8. The results showed that at room temperature, the surfaces of these polymers changed from fluorocarbon rich to hydrocarbon rich as they crystallized . These observations are analogous to another previous observation that the crystallization and molecular orientation of a polymer controls its surface composition regardless of the surface energies of the different components …”