Crystallinity of poly(3‐hexylthiophene) in thin films determined by fast scanning calorimetry

Using fast scanning calorimetry, we determined the crystallinity of thin films of poly(3-hexylthiophene) crystallized from the melt from measurements of the specific melting enthalpy. A broad range of film thicknesses from 10 µm down to 26 nm was covered. The sample mass was determined from measurements of the specific heat capacity in the molten state allowing a quantitative analysis of the heat flow data. Films with a thickness D≥ 400 nm slowly cooled from the melt showed the same crystallinity as bulk samples measured with conventional DSC. Below D≈ 350 nm the melting enthalpy decreased strongly. We assign this strongly reduced crystallinity to the restricted crystallization kinetics originating from hindered spherulitic growth under thin film confinement. A higher crystallinity could be partially regained by extended isothermal crystallization at elevated temperatures. Much faster cooling, with rates above about 100 Ks−1 led to a partial suppression of crystallization even for thick films. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1791–1801