We report on the first exfoliation of MoS2 coaxial nanotubes. The single-layer flakes, as the result of exfoliation, represent the transition metal dichalcogenides' analogue of graphene. They show a very low degree of restacking in comparison with exfoliation of MoS2 plate-like crystals. MoS2 monolayers were investigated by means of electron and atomic force microscopies, showing their structure, and ultraviolet-visible spectrometry, revealing quantum confinement as the consequence of the nanoscale size in the z-direction.
Reversible colour change of leuco dye-based composites is in general closely related to their phase change, thus the two phenomena should occur at around the same temperature and should be influenced similarly. However, spatial confinement of the analysed sample affects the change in colour differently compared to its phase transition and the most pronounced effects can be observed during cooling. The bulk composite is coloured while still liquid and the colour hysteresis does not exhibit a loop. In an open-porous medium the colouration coincides well with the crystallization and the colour hysteresis widens to about 4 °C. Microencapsulated composite exhibits two crystallization processes, one of them taking place at the bulk crystallization temperature and the other one at about 20 °C lower. Under such conditions the composite is coloured just before the onset of the second crystallization, i.e. about 15 °C below crystallization in the bulk, and the corresponding colour hysteresis widens to 18 °C. The two crystallization forms are thermally independent and have the same crystalline structure. These effects should be taken into account when designing future applications where the phase-changing materials are implemented.
The optical properties of black-pigmented solar absorbing paint were analyzed phenomenologically by use of the Kubelka–Munk theory, including correction for reflection on front and rear surfaces. The effective absorption and scattering coefficients and the efficiency curves for absorption and scattering were calculated for coatings with different pigment-to-volume concentration ratios. The dependence of absorption and scattering efficiency on the pigment-to-volume concentration ratio was analyzed by reference to theoretical data in the literature. It was concluded that, during drying and curing of coatings, spherical primary pigment particles most likely collect in elongated groups oriented perpendicularly to the coating surface. Formation of such groups helps in understanding the independent measurements of solar absorptance.
7 April 2011 in Journal of Coatings Technology and Research