Surface induced orientation and vertically layered morphology in thin films of poly(3-hexylthiophene) crystallized from the melt

The presence of interfaces and geometrical confinement can have a strong influence on the structure and morphology of thin films of semicrystalline polymers. Using surface-sensitive grazing incidence wide angle X-ray scattering and atomic force microscopy to investigate the vertical structure of thin films of poly(3-hexylthiophene) crystallized from the melt, we show that highly oriented crystallites are induced at the air/polymer interface and not as sometimes assumed at the interface to the substrate. These crystallites are oriented with their crystallographic a-axis perpendicular to the plane of the film. While the corresponding orientation dominates in thinner films, for sufficiently thick films (>60 nm) a layer containing unoriented crystals is present below the surface layer. Due to the anisotropic charge transport properties, the observed effects are expected to be of special relevance for potential applications of semiconductor polymers in the field of organic photovoltaics for which vertical transport in thicker films plays an important role

Determination of the Crystallinity of Semicrystalline Poly(3-hexylthiophene) by Means of Wide-Angle X‑ray Scattering

Temperature-dependent small-angle and wide-angle X-ray scattering (SAXS/WAXS) measurements on a series of chemically well-defined and highly regioregular poly­(3-hexylthiophenes) were analyzed to determine absolute values of the crystallinities. The analysis is based on the evaluation of the scattered intensity from the amorphous regions providing an easy and fast method for the determination of the crystallinity in the class of side chain substituted polymers. The resulting values are in the range of 68–80% at room temperature depending on the molecular weight. Based on these values, an extrapolated reference melting enthalpy of a 100% crystalline material was determined (Δ<i>H</i>_m^∞ = 33 ± 3 J/g) for use in DSC measurements. For higher molecular weights a decrease of the crystallinity was observed which can be explained by the onset of chain folding as deduced from the analysis of the SAXS patterns. An in-depth analysis based on Ruland’s method showed that the crystalline regions of P3HT exhibit a large amount of internal disorder

Tailoring the Morphology and Melting Points of Segmented Thermoplastic Polyurethanes by Self-Nucleation

It is demonstrated that the melting behavior and the morphology of three segmented thermoplastic polyurethane elastomers (TPUs) can be tailored by applying self-nucleation (SN) procedures. The self-nucleating temperature ranges for each of the TPU have been first determined by differential scanning calorimetry (DSC), while their morphology was studied by polarized light optical microscopy (PLOM), atomic force microscopy (AFM), and small-angle X-ray scattering (SAXS). When the samples are cooled at slow to moderate rates after SN, the crystallization temperature of the TPUs increases by up to 45 °C, when the samples are ideally self-nucleated. This large reduction in supercooling increases the melting points of the samples by approximately 20 °C. At the same time, SAXS and AFM experiments demonstrate the growth of thicker lamellae under these slow to moderate cooling conditions as compared to untreated samples. When ideally self-nucleated samples are rapidly quenched (e.g., at rates of 100 °C min^–1 or larger) from their self-nucleation temperature to room temperature, the effects of SN described above on the morphology and melting points of the samples disappear for the TPUs that do not crystallize fast enough

Crystallization of Poly(ethylene oxide) with a Well-Defined Point Defect in the Middle of the Polymer Chain

Poly­(ethylene oxide) (PEO) is a polymer of great interest due to its prevalence in biomedical, pharmaceutical, and ion conductive systems. In this study, the crystallization behaviors of a PEO with 22 monomer units (PEO₂₂) and a PEO having the same degree of polymerization but with an additional 1,4-disubstituted 1,2,3-triazole ring in central position of the chain (PEO₁₁-TR-PEO₁₁) are investigated. PEO₁₁-TR-PEO₁₁ shows one type of lamella crystal after cooling to <i>T</i> = 0 °C, but structural changes during heating below their final melting are detected by WAXS, DSC, POM, and solid-state NMR spectroscopy. The lamella thickness increases, but simultaneously the helix–helix distance decreases and an additional Bragg reflection appears at 2θ = 22.1°. A model is proposed which explains these structural changes by incorporation of the TR ring into the crystals which are additionally stabilized by attractive C–H···π interactions of the TR rings. Additionally, two different types of extended chain lamella crystals are found in PEO₂₂ by SAXS which are discussed in the context of fractionation caused by the molar mass distribution obtained from MALDI-ToF data

Crystallization of Poly(ethylene oxide) with a Well-Defined Point Defect in the Middle of the Polymer Chain

Poly­(ethylene oxide) (PEO) is a polymer of great interest due to its prevalence in biomedical, pharmaceutical, and ion conductive systems. In this study, the crystallization behaviors of a PEO with 22 monomer units (PEO₂₂) and a PEO having the same degree of polymerization but with an additional 1,4-disubstituted 1,2,3-triazole ring in central position of the chain (PEO₁₁-TR-PEO₁₁) are investigated. PEO₁₁-TR-PEO₁₁ shows one type of lamella crystal after cooling to <i>T</i> = 0 °C, but structural changes during heating below their final melting are detected by WAXS, DSC, POM, and solid-state NMR spectroscopy. The lamella thickness increases, but simultaneously the helix–helix distance decreases and an additional Bragg reflection appears at 2θ = 22.1°. A model is proposed which explains these structural changes by incorporation of the TR ring into the crystals which are additionally stabilized by attractive C–H···π interactions of the TR rings. Additionally, two different types of extended chain lamella crystals are found in PEO₂₂ by SAXS which are discussed in the context of fractionation caused by the molar mass distribution obtained from MALDI-ToF data