Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine)

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Specific heat spectroscopy was used to study the dynamic glass transition of ultrathin poly(2-vinyl pyridine) films (thicknesses: 405-10 nm). The amplitude and the phase angle of the differential voltage were obtained as a measure of the complex heat capacity. In a traditional data analysis, the dynamic glass transition temperature T-g is estimated from the phase angle. These data showed no thickness dependency on T-g down to 22 nm (error of the measurement of +/- 3 K). A derivative-based method was established, evidencing a decrease in T-g with decreasing thickness up to 7 K, which can be explained by a surface layer. For ultrathin films, data showed broadening at the lower temperature side of the spectra, supporting the existence of a surface layer. Finally, temperature dependence of the heat capacity in the glassy and liquid states changes with film thickness, which can be considered as a confinement effect.DFG, Scho-470/20-1, Template confinement effects on discotic liquid-crystal

Dynamic relaxations in a bio-based polyamide with enhanced mechanical modulus

A new grade of bio-based polyamide (PA)—PA meta-xylylene diamine 10 (PA mXD 10)—was investigated. Its first interest is that it permits mild processing conditions at about 200°C. The calorimetric study shows the existence of two cold crystallizations indicative of slow crystallization rate. The glass transition stabilizes at 55°C. By combining calorimetry with dynamic mechanical analysis and dynamic dielectric spectroscopy, we found a perfect consistency between the set of data giving the molecular mobility. The localized relaxations follow Arrhenius equations while the viscoelastic transition follows a Vogel–Fulcher–Tammann law. The compilation of all the relaxation times determined by means of the different analyses highlights a good correlation. This result is perfectly explained by the polarity of the macromolecular chain. The dynamic mechanical behavior showed a storage modulus higher than for the corresponding aliphatic PA and nearly constant until room temperature