TY - JOUR A1 - Madkour, Sherif Aly Hassan Aly A1 - Yin, Huajie A1 - Füllbrandt, Marieke A1 - Schönhals, Andreas T1 - Calorimetric evidence for a mobile surface layer in ultrathin polymeric films: poly(2-vinyl pyridine) JF - Soft matter N2 - 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 Tg is estimated from the phase angle. These data showed no thickness dependency on Tg down to 22 nm (error of the measurement of ±3 K). A derivative-based method was established, evidencing a decrease in Tg 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. PY - 2015 DO - https://doi.org/10.1039/c5sm01558h SN - 1744-683X VL - 11 IS - 40 SP - 7942 EP - 7952 PB - RSC Publ. CY - Cambridge AN - OPUS4-34605 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -