Evaluation of interactions between liquid crystal films and silane monolayers by atomic force microscopy

Atomic force microscopy (AFM) has been used to study forces of intermolecular interactions in two different types of liquid crystal (LC) systems (thermotropic and lanthanide-containing lyotropic ones) with different supramolecular organization and degrees of surface hydrophilization in relation to self-associated silane monolayers on a cantilever probe. Statistical analysis has been applied to the force curves to determine adhesion between liquid crystals and monoassociated layers of trichlorododecylsilane and (3-mercaptopropyl)trimethoxysilane on silicon. The results have been analyzed within the framework of hydrophilic and hydrophobic interactions and compared to the free surface energy values calculated by the Owens, Wendt, Rabel and Kaelble method. Lanthanide-containing liquid crystals demonstrate high value of adhesion work to monoassociated silane monolayers due to their considerable free surface energy. The method of chemical force microscopy (CFM) is found to be applicable to the direct determination of the adhesion force of liquid crystals.