Cold-Crystallization of Poly(trimethylene terephthalate) Studied by Photoluminescence of Its Amorphous Portion

Structural evolution analysis and cold-crystallization kinetics of spherical crystals in poly(trimethylene terephthalate) film using Raman spectroscopy

Dynamic processes and the structural evolution of cold-crystallized poly(trimethylene terephthalate) (PTT) film were investigated using Raman spectroscopy. Raman scattering of C[double bond, length as m-dash]O stretching vibration was related to the molecular chain movement and structure evolution in PTT during cold crystallization. In particular, information about each phase of crystallization, including induction, nucleation, nucleus growth, and secondary crystallization, was thoroughly revealed. The experimental results indicated that the kinetic parameters measured by the Raman method were in good agreement with those obtained by differential scanning calorimetry (DSC) and infrared spectroscopy. The blue-shifted C[double bond, length as m-dash]O stretching vibration resulting from the crystallization process is a popular phenomenon and may therefore have many potential applications in a wide range of areas.

Nanostructuring thin polymer films with optical near fields

In the present work, we report on the application of optical near fields to nanostructuring of poly(trimethylene terephthalate) (PTT) thin films. By exposure to a single ultraviolet nanosecond laser pulse, the spatial intensity modulation of the near-field distribution created by a silica microsphere is imprinted into the films. Setting different angles of incidence of the laser, elliptical or circular periodic ring patterns can be produced with periods as small as half the laser wavelength used. These highly complex patterns show optical and topographical contrast and can be characterized by optical microscopy (OM) and atomic force microscopy (AFM). We demonstrate the key role of the laser wavelength and coherence length in achieving smooth, extended patterns in PTT by using excimer laser (193 nm) and Nd:YAG laser (266 nm) pulses. Reference experiments performed in Ge2Sb2Te5 (GST) demonstrate that nanopatterning in PTT is triggered by ablation as opposed to GST, in which nanopatterning originates from laser-induced phase change, accompanied by a small topographical contrast. The experiments presented in this work demonstrate the suitability of optical near fields for structuring polymer films, opening up new possibilities for nanopatterning and paving the way for potential applications where optical near fields and polymer nanostructures are involved.

Assessment of femtosecond laser induced periodic surface structures on polymer films

In this work we present the formation of laser induced periodic surface structures (LIPSS) on spin-coated thin films of several model aromatic polymers including poly(ethylene terephthalate), poly(trimethylene terephthalate) and poly carbonate bis-phenol A upon irradiation with femtosecond pulses of 795 and 265 nm at fluences well below the ablation threshold. LIPSS are formed with period lengths similar to the laser wavelength and parallel to the direction of the laser polarization vector. Formation of LIPSS upon IR irradiation at 795 nm, a wavelength at which the polymers absorb weakly, contrasts with the absence of LIPSS in this spectral range upon irradiation with nanosecond pulses. Real and reciprocal space characterization of LIPSS obtained by Atomic Force Microscopy (AFM) and Grazing Incidence Small Angle X-ray Scattering (GISAXS), respectively, yields well correlated morphological information. Comparison of experimental and simulated GISAXS patterns suggests that LIPSS can be suitably described considering a quasi-one-dimensional paracrystalline lattice and that irradiation parameters have an influence on the order of such a lattice. Fluorescence measurements, after laser irradiation, provide indirect information about dynamics and structure of the polymer at the molecular level. Our results indicate that the LIPSS are formed by interference of the incident and surface scattered waves. As a result of this process, heating of the polymer surface above its glass transition temperature takes place enabling LIPSS formation.