ABSTRACT:New methods to visualize polymer morphologies in three-dimension (3D) in polymer science are reviewed. Here we concentrate on one of such 3D imaging technique, transmission electron microtomography (TEMT), and introduce some experimental studies using this novel technique. They are block copolymer morphologies during order-order transition between the two different morphologies and block copolymer thin film morphology also during morphological change due to confinement. Direct visualization of 3D structure of silica particle/rubber composite and related morphological analyses are shown. Subsequently, as a very hot topic of the 3D imaging, we show for the first time to characterize the morphological change in a silica particle/rubber composite upon stretching. It was found that the aggregates of silica particles were broken down upon stretching and many voids were generated near and between the silica particles. Local stress upon stretching inside the composite was inferred from the image intensity of the 3D reconstructed image. The local stress was found not only near the silica particles but also near the top of the voids. The observations indicated that the local stress increases the modulus, causing voids to form along the stretching direction. The thickness of the specimen after the stretching was also estimated from the 3D volume data, which turned out to be non-uniform and thinner than what is expected from the affine deformation. These experimental findings indicate that the rubber composite does not obey the assumption of the affine deformation at the nano-scale. Polymer materials are ubiquitous in our daily life. Such materials often consist of more than one species of polymers and thus become multi-component systems, such as in polymer blends, 1,2 block copolymers, 3 and fillers/polymer composites. 4 The multi-component systems often show phase-separated structures due to immiscibility of constituents. Studies to characterize such morphologies inside the materials have been growing intensively over the past few decades. Academic interest in complex fluids (to which polymeric systems belong) as well as the ceaseless industrial need for developing new materials motivates such studies.In academia, pattern formation and self-assembling processes of multi-component polymer systems are one of the most fascinating research themes in nonlinear, non-equilibrium phenomena.1 Likewise, nanometer-scale periodic structures formed in block copolymers in their equilibrium state are interesting because their self-assembly is driven by the subtle balance between the entropic block chain conformation and enthalpic interaction between the constituents. 3In industry, phase-separated polymer systems provide an important route to achieve superior physical properties. Hence, the structure-property relationship in multi-component polymeric materials is of significant importance, basic studies on which eventually render new designs of polymer materials satisfying the diverse requirements of industry.Filler/polymer comp...
Energy-filtering transmission electron microscopy (EFTEM) was employed for investigating interactions between rubber and ZnO particles in the accelerated vulcanization process. Combining elemental mapping and electron energy loss spectroscopy (EELS) by EFTEM enabled the characterization of the interfaces with spatial resolutions of less than 10 nm and with high elemental detection sensitivity. We found that a sulfur- and zinc-rich compound was generated around ZnO particles, and that product was then revealed to be ZnS-generated as a byproduct in the accelerated vulcanization process. Through this study, it is indicated that the accelerated vulcanization with ZnO does not occur uniformly in the rubber matrix; it occurs locally around ZnO particles at a higher reaction rate, implying that the rubber network structure is not uniform on the nanoscale.
The molecular dynamics and orientation of vulcanized natural rubber (NR) stretched at a low extension ratio (a¼stretched length/ original length) were studied by carbon-13 direct polarization-magic angle spinning nuclear magnetic resonance ( 13 C DP-MAS NMR), 13 C cross-polarization (CP)-MAS NMR, 13 C DP NMR without MAS, 13 C CP NMR without MAS and density functional theory (DFT) calculations. Gradual peak broadening was observed in the 13 C DP-MAS NMR spectra of stretched NR with an increasing extension ratio, indicating that the molecular mobility of NR chains is restricted by stretching. The static 13 C NMR spectra of uniaxially stretched NR (a¼2) changed slightly depending on the angle, h, between the stretching direction and the applied magnetic field, although the spectra of unstretched NR did not change even if h was changed. Thus, it is noted that NR chains oriented slightly as a time average by stretching even at a low extension ratio, a¼2, although there still exists rapid rotation around the oriented NR chain. Motionally narrowed anisotropies in the 13 C spectra of stretched NR and the directions of chemical shift anisotropy principal axes determined by DFT calculations suggest that isoprene units of oriented rubber chains in stretched NR rotate rapidly around the axis that almost aligned with the C¼C bond direction of polyisoprene.
The analysis of the molecular orientation of stretched rubbers is of great importance to understand rubber elasticity. To characterize this orientation, X-ray diffraction [1][2][3] and AFM 4 data have been reported. Toki et al. carried out in situ synchrotron X-ray diffraction measurements for natural rubber (NR), [1][2][3] and reported that 75% of polymer chain segments remain unoriented even at a large strain with extension ratio of ¼ 6. At smaller strains with extension ratios, 2, the wide-angle X-ray diffraction (WAXD) images show only amorphous halo patterns and no oriented segments were found.3 X-ray diffraction method is very useful to detect oriented crystalline components. However, rubbers are mostly amorphous under small strains, and it is difficult to observe oriented amorphous components by X-ray diffraction method. Moreover, rubbers have high molecular mobility, which makes the X-ray diffraction analysis more difficult.In this study, solid-state 13 C NMR measurements are carried out on stretched vulcanized NR at extension ratio of ¼ 2 to investigate molecular orientation. Solid-state NMR is a powerful method to detect molecular orientations even for mobile amorphous samples, and therefore, it is quite suitable for the study's purpose to detect the molecular orientation of rubber samples. EXPERIMENTALThe vulcanized NR sample used in this study has been cured at 170 C for 10 min. with sulfur of 1.5 phr, ZnO of 3.0 phr, stearic acid of 2.0 phr and an accelerator of 0.5 phr. A vulcanized rubber sample with an inner diameter of 2.5 mm is prepared using this procedure.NMR measurements are carried out by a Bruker Avance 400 spectrometer, equipped with static probes operating at 100.6 MHz for 13 C. Rubber bands without stretching condition are measured by 13 C direct polarization (DP) with 1 H dipolar decoupling (DD) in the static state at 25 and À55 C. The S/N ratio of the 13 C spectrum at À55 C was not excellent, therefore, the spectrum with cross polarization (CP) at À55 C is also measured. The DP and CP static spectra under 1 H DD condition were essentially equivalent. For a stretched sample, the rubber bands are uniaxially stretched by covering a thin teflon plate, which results in ¼ 2 (see Figure 1a). The angle, , of the teflon plate, which corresponds to the stretching direction with respect to the applied static magnetic field, B 0 , is changed in the static probe, as shown in Figure 1b. The 13 C DP/DD spectra are obtained for all the stretched samples at 25 C. The =2 pulse widths were 8.5 and 4.35 ms for the measurements at 25 and À55 C, respectively. 1 H dipolar decoupling field strengths of 29.4 and 57.5 kHz have been applied during the detection of free induction decay at 25 and À55 C, respectively. All the measurements of stretched rubbers were carried out 10-20 min. after stretching. The delay time was 4-5 s. Figure 2 shows the 13 C dipolar decoupling (DD)-static NMR spectra of unstretched vulcanized NR at À55 (a) and 25 C (b). The structure of polyisoprene, which is the major constituent of n...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.