Structural Evolution Mechanism of Crystalline Polymers in the Isothermal Melt-Crystallization Process: A Proposition Based on Simultaneous WAXD/SAXS/FTIR Measurements

Abstract

Time-resolved simultaneous measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) (and FTIR spectra) were performed for various kinds of crystalline polymers in isothermal melt-crystallization processes, from which the common features of the structural evolution process as well as the different behaviors intrinsic to the individual polymer species were extracted. The polymers targeted here were polyethylene, isotactic polypropylene, polyoxymethylene, aliphatic nylon, vinylidene fluoride copolymer, trans-polyisoprene, and poly(alkylene terephthalate). A universal concept of the microscopically viewed structural evolution process in isothermal crystallization may be described as follows: (i) the small domains composed of locally regular but more or less disordered helical chain segments are created in the melt (this important information was obtained by the IR spectral data analysis); (ii) these domains grow larger as the length and number of more regular helical segments increase with time; (iii) the correlation among the domains becomes stronger and they approach each other; and (iv) they merge into the stacked lamellar structure consisting of the regularly arranged crystalline lattices. The inner structure of the domains is different depending on the polymer species, as known from the IR spectral data

Bio-Based Polyamide 1010 with a Halogen-Free Flame Retardant Based on Melamine–Gallic Acid Complex

“…Only some remarks can be made at this point, first regarding the structural behavior of PA1010, which was dominated by the different mobility of the NH– and CO-side methylene segments and secondly related to the cis–trans isomerization of secondary amide groups responsible to the formation of hydrogen bonds. It was observed that in the lamellar structure the NH-side methylene chains remain in the disordered state a long time after the CO-side methylene chains are parallel arrayed and the intermolecular hydrogen bonds were formed [ 46 ]. Our results seem to be in agreement with these findings, as it was already shown in the case of methylene stretching modes in the 2920–2850 cm −1 region.…”

High-Electric-Field-Induced Hierarchical Structure Change of Poly(vinylidene fluoride) as Studied by the Simultaneous Time-Resolved WAXD/SAXS/FTIR Measurements and Computer Simulations

“…The present experiments were performed by combining the various kinds of ideas and techniques: (a) the application of a cyclic high electric field to the thin film (which caused the easy breakdown of the film), (b) the time-resolved simultaneous measurements of the SAXS/WAXD/FTIR data for such a thin film by the irradiation of the powerful synchrotron-undulator-sourced X-ray beam (which caused also the easy sample damage), (c) the measurement of IR spectral data in a transmission mode to collect the quantitative spectral profiles, not deformed by the reflection-type measurement mode, , (d) the rapid and repeated collection of a series of the data using the computer-controlled system, and (e) the quantitative analysis of the big data collected in the WAXD/SAXS/IR experiments. We have managed to extract the several important pieces of information from these analyses and proposed the mechanism of the electric-field-induced inversion mechanism viewed from the various hierarchical structure.…”

“…Figure shows a block diagram of the whole measurement system. A miniature FTIR spectrometer (α, Bruker) was set around the sample holder to measure the transmission-type IR spectra at a constant time interval. , The WAXD detector [a flat panel (Hamamatsu Photonics, K. K.) or a Pilatus 100k or a Pilatus 300k (Dectris)] was set at the position about 10 cm distant from the sample holder. The SAXS detector [an image-intensified charge-coupled device (CCD) (Hamamatsu Photonics K. K.) or Pilatus 300k (Dectris)] was set at about 2 m distance from the sample position through the vacuum pipe to depress the air scattering.…”

“…These three kinds of methods must be used simultaneously and at a short time interval for one sample subjected to an external electric field. 13,14 This is because the hierarchical structure will be changed quite sensitively depending on the electric field strength and the longer exposure of X-ray beam causes the breakage easier.…”

“…The concrete methodology for this purpose is the combined usage of synchrotron-sourced wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and transmission-type IR spectroscopy. These three kinds of methods must be used simultaneously and at a short time interval for one sample subjected to an external electric field. , This is because the hierarchical structure will be changed quite sensitively depending on the electric field strength and the longer exposure of X-ray beam causes the breakage easier.…”