Articles written in Bulletin of Materials Science
Volume 39 Issue 1 February 2016 pp 229-234
Radical coupling was used to modify graphite with maleic anhydride (MAH). Azobisisobutyronitrile (AIBN) as radical generator activated MAH radically and it was reacted with defects at the surface of nanolayers. A set of batches with different reaction times (24, 48 and 72 h) were performed to obtain fully-modified nanolayers (GMA1, GMA2 and GMA3, respectively). Fourier transform infrared results approved the synthesis of MAHgrafted graphite. Thermogravimetric analysis showed that 5.9, 11.1 and 13.2 wt% of MAH was grafted onto the surface of GMA1, GMA2 and GMA3, respectively, and that was approved by X-ray photoelectron spectroscopy results. Also, X-ray diffraction patterns showed that $d$-spacing increased from 0.34 nm for graphite to 1.00 nm for all modified samples. However, GMA1 showed a weak peak related to graphite structure that disappeared when reaction time was increased. After modification with MAH, lamella flake structure of graphite was retained whereas the edges of sheets became distinguishable as depicted by scanning electron microscopy images. According to Raman spectra, modification progression resulted in more disorder structure of nanolayers due to grafting of MAH. Also, transmission electron microscopy images showed graphite as transparent layers while after modification, surface of nanolayers became folded due to the opposite effects of $\pi$-conjugated domains and electrostatic repulsion of oxygen-containing groups.
Volume 42 Issue 5 October 2019 Article ID 0219
In this study, hybrid composites of polyurethane-acrylate (PUA) and silica nanoparticle were prepared by a radical method. For this aim, silica nanoparticles were chemically functionalized with 3-methacryloxypropyltrimethoxysilane. Polyurethane was synthesized and then modiﬁed with 2-hydroxyethyl methacrylate to yield PUA. Then, different amounts of modiﬁed-silica were used to prepare PUA composites by the addition of an ethylene glycol dimethacrylate crosslinker. Fourier-transform infrared spectroscopy conﬁrmed the successful functionalization of silica nanoparticles and the prepa-ration of PUA. Structural investigation of the functionalized-nanoparticles and also nanocomposites was carried out using X-ray diffraction and electron microscopy. According to the thermal gravimetric analysis results, char residue of HSiO₂ is 86.6%, which decreases to 81.3% in the case of MSiO₂ as a result of its modiﬁer degradation content of 5.3%. PUAS5 shows main decomposition temperatures of 396.5 and 454.9°C and also char content of 5.7% at 700°C. The high amount of MSiO₂ can also be resulted in higher degree of crosslinking and therefore higher thermal stabilities and char residue.
Volume 44 All articles Published: 1 July 2021 Article ID 0199
The poly(amidoamine) (PAMAM) dendrimer-grafted silica nanoparticles were utilized as a curing and composite agent for epoxy-terminated polyurethane (PU). For this purpose, surface-hydroxylated silica nanoparticles (SiH) were modified with (3-aminopropyl)triethoxysilane to obtain the core for PAMAM dendrimer synthesized via consecutive addition of methyl acrylate and ethylenediamine. Effect of different chain extenders, pyromellitic dianhydride (PMDA) and 1,4-butanediol (BD), on thermal characteristics of the composites was also studied in detail. Successful incorporation of PMDA and BD chain extenders and also epoxy groups to the PU backbone was confirmed by proton nuclear magnetic resonance analysis. Chemical modification of silica nanoparticles via PAMAM dendrimer in each of the generation steps was studied using Fourier-transform infrared spectroscopy and also their thermal degradation characteristics. The thermogravimetric analysis results proved that increasing content of the PAMAM-modified silica nanoparticles in combination with incorporation of PMDA as the chain extender resulted in higher thermal stabilities of the PU composites. The cured epoxy-modified PU with PMDA chain extender showed higher char residue compared with the cured epoxy-modified PU with BD chain extender (7.1 against 0.8%). X-ray diffraction analysis confirmed amorphous nature of silica and the PU composites. Scanning and transmission electron microscopies were also used for morphological investigation of the pure and PAMAM-modified silica in addition to the PU composite.
Volume 44, 2021
Continuous Article Publishing mode
Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020
Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020
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