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Hierarchical spatial heterogeneity in liquid crystals composed of graphene oxides
Shundo, Atsuomi,Hori, Koichiro,Penaloza, David P.,Matsumoto, Yuji,Okumura, Yasushi,Kikuchi, Hirotsugu,Lee, Kyung Eun,Kim, Sang Ouk,Tanaka, Keiji The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.32
<P>Graphene oxide (GO) is a class of two-dimensional materials with a thickness of about 1 nm and a broad distribution of lateral dimension commonly approaching several micrometers. A dispersion of GOs in water often forms a liquid crystal, which is expected to be a promising precursor for the fabrication of carbon-based materials with well-ordered structures. To accelerate the application of GO-based liquid crystals, their structures and physical properties at various sizes must be well understood. To that end, we examined the local rheological properties of GO-based liquid crystals in the nematic phase using a particle tracking technique, where local properties can be accessed by observing the thermal motion of embedded probe particles. Particle diffusion was spatially heterogeneous, and depended on the size of the particles. Such a size-dependent heterogeneity can be associated with a hierarchical local environment, which is time-dependent for this system. The anisotropic particle diffusion originated from particles trapped in between the GO layers and in isotropic-like regions. The aggregation states of the GO dispersion composed of nematic and isotropic-like regions were observed using confocal laser scanning microscopy.</P>
Off-stoichiometry Effect on Network Structure and Tensile Properties of an Epoxy Resin
Kosuke Mitsuki,Atsuomi Shundo,Satoru Yamamoto,Keiji Tanaka 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.2
Epoxy resins, which have a network structure formed via curing reactions of epoxy and amine compounds, are often used as a composite with inorganic fillers. In general, either an epoxy or amine component was segregated at the filler interface, meaning that the reaction at the interface would proceed non- stoichiometrically. The objective of this study is to give a better understanding of how off-stoichiometry affects the network, thereby the material properties. The epoxy resins were obtained by the reaction of di-functional epoxy and amine compounds at various ratios (p). Higher p value corresponds to an excess of epoxy groups compared to amino ones. The glass transition temperature decreased with increasing p, suggesting a plasticizing effect of unreacted epoxies. Young’s modulus remained unchanged at a lower p, while it started to decrease at a higher p. Discussion on the correlation with the network will be given.