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The effects of graphene oxide (GO) on the early-age hydration process and mechanical properties of Portland cement paste were experimentally investigated in this study. Based on an isothermal calorimeter measurement, the hydration rate of cement was observed to increase with the increase of GO content by nucleation effect. On the other hand, the electrical resistivity development of GO-cement paste was monitored using a non-contact electrical resistivity device. The result showed that electrical the resistivity of GO-cement paste was evidently higher than that of plain cement paste. However, cement paste with excessive amounts of GO exhibited a decreased electrical resistivity due to the massive ion diffusion caused by GO. Compared to plain cement paste, the GO-cement paste exhibited obviously higher compressive and flexural strengths, but the enhancements in compressive strength began to decline when the GO amount was greater than 0.04%. The microstructure characterization indicated that GO can apparently densify the cement pastes with less

wileyonlinelibrary.comThird, monolayer TMDs show piezoelectricity due to the broken inversion symmetry. [5,6] As a result, monolayer TMDs indicate significant potential for flexible optoelectronics, [7,8] piezotronics, [5,6] mechanically enhanced nanocomposites, [9] and smart materials for strain sensing. [10] In these applications, strain is inevitably a critical object requiring comprehensive understanding.So far, substantial efforts have been spent on the study of strain engineering to the band structure of TMDs by using bending, [11][12][13][14][15] high-pressure compression, [16][17][18][19][20][21][22][23][24] and tensile elongation. [25] Their results indicate strain is an effective way to tune the bandgap from direct to indirect, generate the redshifts of trion and exciton peaks, and change the material conductivity from semiconducting to metallic. [26] However, an important question of how strain relaxes inside TMDs is still open.Herein, we investigate the strain relaxation of monolayer WS 2 triangular crystals deposited on polydimethylsiloxane (PDMS) substrate. The uniaxial tensile strain applied to the WS 2 crystals is transferred from PDMS substrate when the substrate is elongated by a loading frame. We observe that the trion and exciton PL peaks undergo a redshift when the substrate strain is increased from 0 to 0.16. However, the redshifts stop when the substrate strain is further increased from 0.16 to 0.32. This is caused by the strain relaxation in WS 2 through Strain-dependent electrical and optical properties of atomically thin transition metal dichalcogenides may be useful in sensing applications. However, the question of how strain relaxes in atomically thin materials remains not well understood. Herein, the strain relaxation of triangular WS 2 deposited on polydimethylsiloxane substrate is investigated. The photoluminescence of trions (X -) and excitons (X 0 ) undergoes linear redshifts of ≈20 meV when the substrate tensile strain increases from 0 to 0.16. However, when the substrate strain further increases from 0.16 to 0.32, the redshifts cease due to strain relaxation in WS 2 . The strain relaxation occurs through formation of wrinkles in the WS 2 crystal. The pattern of wrinkles is found to be dependent on the relative angle between an edge of the triangular WS 2 crystal and tensile strain direction. Finite element simulations of the strain distribution inside the WS 2 crystals explain the experimental observations.

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Exfoliation and dispersion of boron nitride nanosheets (BNNSs) is the key to achieving desired reinforcing effects for ordinary Portland cement (OPC). Few studies exist, however, of the dispersion of BNNSs in a cement-induced alkaline environment and their effect on the mechanical properties of normal OPC paste. In this study, protocols were developed to prepare BNNS-reinforced OPC paste. Ultrasonication was used to exfoliate BNNSs from h-BN in water based suspensions. The addition of surfactants in the suspension was found to hinder the exfoliation of the BNNSs. The surfactants were, however, found to be essential for the dispersion of the BNNSs in pore solution. Among the three surfactants used in this study, polycarboxylate based superplasticizer was most suitable as it maintained over 40% of the BNNSs stable in the pore solution for 4 hours and increased the hydration flow peak over 20%. Atomic force microscopy results indicated that the thickness of the BNNSs was mostly under 10 nm. With the addition of 0.003 wt% BNNSs, the compressive and tensile strengths of the cement were increased by 13% and 8%, respectively. Besides the nucleation effect as indicated by hydration heat, pore structure refinement and chemical bonding were also found as the main reinforcing mechanisms of BNNSs in OPC matrix.