Download is available until [expire_date]
  • Version
  • Download 5
  • File Size 392.48 KB
  • File Count 1
  • Create Date June 18, 2023
  • Last Updated June 18, 2023

Abstract_Serguei Savilov

Present lecture is focused on the nanoscale effect. In spite it is well described during last decades, almost any new research opens new horizons. Carbon - one of the most important in our life and at the same time - most abundant element at the Earth - can serve as an ideal example for demonstrating nanoscale effect. The chemistry of carbon is extremely interesting due to the multitude of its allotropic modifications (graphite, graphene, diamond, lonsdaleite, fullerene, carbon nanotubes, etc.), which demonstrate various, sometimes opposite, characteristics. Starting from thermodynamics, it is important to note, that almost half century ago it was fixed that the triple point at the state diagram is shifted for graphite in the bulk state and for its cluster for thousands of atoms. That is why so important to understand structural features of the compounds at the levels, higher than atomic, but lower than micron. Sometimes the existence of the particles with so small size is impossible without stabilization by, e.g. functional groups, that can be also demonstrated on carbon nanotubes or few-layer graphene fragments which are characterized by a continuous, extended structure, consisting of 1–10 carbon layers. Depending on the number of layers and particle size their planarity, associated with the number of carbon atoms with uncompensated valences and functional groups, can vary. These changes can be traced using their heats of formation, calculated from DCS data or bomb calorimetry. The morphology of the objects can be investigated by HRTEM, whale the surface composition at the depth of 1 nm - by XPS. Some unusual effects - like a trap of Fe single atoms between functionalized carbon layers - can be studied by synchrotron radiation-based X-ray absorption spectroscopy (XAS) method actual for ppb concentration level.

The transition to nanoscale derivatives for much more complicated objects, such as cellulose, deal with decrease of "fundamentality" of the research but sufficient rise of its practice significance. The structure of cellulose is formed from repeating units. Each next unit is inverted from the previous one, giving the molecule a flat ribbon conformation. Due to the linearity and stereoregularity cellulose molecules forms extended spatial macrocomplexes. Due to a network of hydrogen bonds amorphous and crystalline regions in microfibrils exists together. Modern synthetic approaches allow researchers to remove these anistropic fragments -microcrystalline and nanocrystalline celloloses, demonstrating many effects, which are important for the practical use.

By admin

Leave a Reply

Your email address will not be published.