Physico-Chemical nanomaterials science

Investigation of the structure and thermal motion in nanostructured 1-octadecene

K.I. Hnatiuk1, A.N Alekseev1, S.A. Alekseev1, Yu.E. Grabovsky1, M.M. Lazarenko1, M.V. Lazarenko2

1 Taras Shevchenko National University of Kyiv, Physical Faculty, Volodymyrs’ka St. 64/13, Kyiv 01601, Ukraine.
E-mail: email.of. corresponding_20gnatk@gmail.com
2 National University of Food Technologies, Volodymyrs’ka St. 68, Kyiv-01601, Ukraine.

The wide use of the properties of nanomaterials leads to the need to analyze how the basic concepts of condensed-state physics, such as the tight packing principle, phenomenology and thermodynamics of phase transitions, as well as molecular mobility and diffusion properties, change when this scale is reached.
Little is known about the effect of confined space on the equilibrium and kinetic properties of matter, as well as on phase transitions in the solid state. The influence of the pore geometry, in particular the shape of the pores on these properties, has not been sufficiently studied.
In this paper, we investigate the thermal motion, structure, and phase transitions in a nanoscale system based on porous silicon and chain molecules of 1-octadecene, the length of which is comparable to the average pore diameter.
The effect of a confined space of silicon nanopores on the structure, thermal motion, and phase transformations in 1-octadecene crystals is studied. With the help of thermophysical methods, IR spectroscopy and X-ray phase analysis, the temperature of the phase transitions in the solid state and the melting point were lowered. It was also found that 1-octadecene both in a porous matrix of silicon and in the bulk crystallizes with an orthorhombic sub-cell, but the size of the crystallites vary. As a result of the formation of 1-octadecene crystals in the silicon pores, the pore size decreases from 200 nm to 1.4 nm, is a consequence of the formation of central cylindrical pores in 1-octadecene during its crystallization in silicon pores. A phase transition in the boundary layer is detected. A model of topological solitons is proposed for the qualitative description of the thermal motion of molecules in this system.