Analyzing Morphology and Thermal History of Polybutylene Terephthalate by THz Time-domain Spectroscopy
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Analyzing Morphology and Thermal History of Polybutylene Terephthalate by THz Time-domain Spectroscopy Steffen Wietzke & Marco Reuter & Nikolaus Nestle & Evgueni Klimov & Uri Zadok & Bernd M. Fischer & Martin Koch
Received: 6 July 2011 / Accepted: 8 July 2011 / Published online: 20 July 2011 # Springer Science+Business Media, LLC 2011
Abstract We have measured the frequency-dependent dielectric function of semicrystalline polybutylene terephthalate (PBT) in the terahertz region between 100 GHz and approximately 2.8 THz. A characteristic band is observed around 2.38 THz. The intensity of this band is a good indicator of the degree of crystallinity of the different samples. A potential assignment of this band is proposed, based on the comparison with spectroscopic data of the structurally very similar polyethylene terephtalate (PET). Furthermore, the frequency-dependent index of refraction of PBT reveals more insight about the morphology and different thermal history of the samples under investigation. Keywords Terahertz time-domain spectroscopy . Polybutylene terephthalate . PBT . Degree of crystallinity . Morphology . Structure . Macromolecule . Index of refraction . Refractive index . Absorption coefficient . Thermal history . Amorphous domains . Semi-crystalline polymer . Non-destructive . Analysis
1 Introduction Some of the first far-infrared spectra of polymers have been reported as early as 1960 [1]. Since then the steady progress in the improvement of the spectroscopic devices has spurred S. Wietzke (*) : M. Reuter : B. M. Fischer : M. Koch Fachbereich Physik, Philipps-Universität Marburg, Renthof 5, 35032 Marburg, Germany e-mail: [email protected] N. Nestle : E. Klimov BASF SE, Polymer Physics Research, 67056 Ludwigshafen, Germany U. Zadok Novatrans Group SA, 60 Ramat Yam St., Herzelia 46851, Israel Present Address: S. Wietzke ContiTech AG, R&D Materials, Philipsbornstr.1, 30165 Hannover, Germany
J Infrared Milli Terahz Waves (2011) 32:952–959
953
the publications of several more detailed studies, including for example temperaturedependent spectra [2–4] and comparisons between isotopic labelled samples [5]. Whereas near- and mid-infrared spectroscopy considers mainly absorption peaks that arise from highly localized intramolecular deformation such as hindered rotation or stretching oscillation of covalent bonds [1], the far-infrared (FIR) or terahertz (THz) frequency range between 100 GHz and approximately 6 THz (3–200 cm−1) is of particular interest for the investigation of complex molecular structures and intermolecular networks [6]. In particular, FIR and THz waves interact with collective motions of large molecules such as inter- and intramolecular vibrations of the polymer chains, allowing for the identification of complex molecular interactions like skeletal vibrations, libration of side groups, intermolecular vibrations in the crystalline phase [7], or vibrational modes of hydrogen bonds [8–10]. The development of THz time-domain spectroscopy (THz TDS) a few decades ago [11] was follow
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