Nanocrystallite-liquid phase transitions are studied for 1-octadecene confined in the pores of chemically functionalized silica gels. These silica gels possess similar fractal geometries of the pore system but differ in chemical termination of the surface, specific surface area (F) and pore volume (V). Linear dependencies of the melting temperature and specific melting heat on the F/V ratio are found for a series of silica gels with identical surface termination. A thermodynamic model based on experimental data is established, which explains the observed shift of the phase transition parameters for porous matrices with different surface chemistries. In addition, this model allows evaluation of actual changes in nanocrystallite density, surface tension and entropy upon melting.

Nanocrystallite–liquid phase transition in porous matrices with chemically functionalized surfaces

Topological solitons in chain molecular crystals with stoichiometric obstacles and hydrogen bonds

Melting of crystalline compounds inside the nanopores of open-morphology porous systems was studied on a model system, consisted of 1-octadecene and silica gels with different pore sizes, by means of thermogravimetry, differential scanning calorimetry and powder X-ray diffraction. The parameters of silica gels porous structure (surface area, pore size and volume) were calculated using N2 adsorption data. To describe the experimental results, a new thermodynamic model of crystallites melting inside the nanopores of irregular shape was established. This model allows an analytical prediction for the shift of phase transition temperature and melting enthalpy (latent heat of melting) due to the surface tension effects. To a first approximation, both parameters must linearly depend on the specific ratio of the total surface of pores to their total volume, and experimental studies have mostly confirmed this result for the melting of 1-octadecene confined inside the pores of a wide range of various silicas (with the pores of different sizes and geometry).

Melting of 1-octadecene inside the pores of open-morphology silica gel: thermodynamic model and experimental studies

We have compared the structure, phase transitions and the thermal motion mechanisms of the undecylenic acid in bulk and inside a porous matrix using powder X-ray diffraction, calorimetry and IR-spe...

Investigation of the structure and mechanisms of thermal motion in nanostructured undecylenic acid

Topological solitons in aliphatic systems with a restricted translational mobility

Influence of confined space of silicon nanopores on the structure, thermal motion and phase transitions of 1-octadecene crystals was studied by powder XRD, FTIR and thermophysical methods. ...

Yu. E. Grabovsky

Papers

Structure and thermal motion of 1-octadecene, confined in the pores of porous silicon

Investigation of the structure and mechanisms of thermal motion in nanostructured undecylenic acid