Application of temperature modulation to FTIR spectroscopy: an analysis of equilibrium and non-equilibrium conformationa
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Application of temperature modulation to FTIR spectroscopy: an analysis of equilibrium and non‑equilibrium conformational transitions of poly(ethylene terephthalate) in glassy and liquid states Valerio Di Lisio1 · Elisa Sturabotti1 · Iolanda Francolini1 · Antonella Piozzi1 · Andrea Martinelli1 Received: 19 November 2019 / Accepted: 4 August 2020 © The Author(s) 2020
Abstract In this paper, the application of a temperature modulation to the temperature-resolved FTIR analysis is reported. The advantage offered by the spectroscopic investigation, able to follow the micro-structural and conformational sample modification involved in sample thermal transformation, was merged to that of temperature modulation, related to the possibility to separate the reversing (in-equilibrium within the experimental condition) to the non-reversing (non-equilibrium) processes. The potentiality of the technique (modulated temperature FTIR, MTFTIR) is highlighted through the study of the thermal transitions of amorphous poly(ethylene terephthalate) from 50 °C to the cold-crystallization. After the presentation of the theoretical framework and the experimental conditions, a step-by-step description of acquired data elaboration is given. The total variation of a selected band intensity as function of mean temperature as well as its reversing and non-reversing components are obtained. The evolution of the bands at 1340 and 971 cm−1, assigned to the trans conformation of the ethylenic unit and to the all-trans conformation of the repeating unit, respectively, are investigated. As expected, the glass transition is observed in the reversing components meanwhile the recovery of the glass relaxation and cold crystallization in non-reversing ones. Particularly interesting resulted the behaviour of the sample in the supercooled liquid state, between the glass transition and the cold-crystallization onset, in which the results show that the ethylenic conformers are in-equilibrium while the all-trans sequences are not. MTFTIR is confirmed to be a technique particularly suitable for the characterization of non-equilibrium conformational states of polymers. Keywords MTFTIR · Modulated temperature · Poly(ethylene terephthalate) · Conformational rearrangement · Nonequilibrium transition · Liquid relaxation
Introduction Thermal analysis is considered one of the main issues in materials characterization, both from the applicative and fundamental research point of view [1]. A comprehensive definition of material properties, investigated under different aspects, can be pursued and achieved successfully by combining different techniques, methods Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10973-020-10169-0) contains supplementary material, which is available to authorized users. * Valerio Di Lisio [email protected] 1
Department of Chemistry, Sapienza University of Rome, P.le A. Moro 5, 00185 Rome, Italy
and experimental conditions [2]. In particular, the complex thermal transformations
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