Nanocomposite Materials: The Boundary Layer and the Thermodynamics of Inclusion Melting

In the present paper, we formulate a thermodynamic model to describe the melting of inclusions with a boundary layer in nanopores. Within the scope of this task, we define the conditions for melting and describe how the temperature and heat of fusion of the inclusion are related to the size of the inclusion and its boundary layer. Experimental validation of the model is performed using silica gel matrices with different pore sizes containing inclusions of 1-octadecene and undecylenic acid. We report that both the melting point and the specific heat of fusion in such systems decrease with decreasing sizes of nanoinclusions. The results of the experiment agree well with the predictions of the model. The model described is then used to develop a method for determining the thickness of the inclusion's boundary layer based on experimental data of the inclusion's melting parameters. We apply this method to 1-octadecene and undecylenic acid and further use it to elucidate the process of inclusion formation for chain molecules in silica gel-based nanocomposites.