Physico-Chemical nanomaterials science
Lowering of friction in monolayers of C24H50/C48H98 mixture
Kutsenko V.Ye. and Vasko A.A., Marchenko O.A., Senenko A.I.
Physical Electronics Department, Institute of Physics of the NAS of Ukraine. Prospect Nauki, 46, Kyiv-03680, Ukraine. 
E-mail: artem.vasko@ukr.net

Self-assembly at the solid/liquid interface is widely used for designing surfaces with pre-determined physical properties (electrical, optical, wetting, lubrication, etc.), which strongly depend on molecule/molecule interactions and molecule/surface one. In turn, balance between these interactions is critically affect morphology of monolayer [1]. The linear adsorbates such as normal alkanes and substituted-alkane molecules deposited on the basal surface of graphite are promising objects for establishing correlation between monolayers morphology and its friction properties.
Monolayers formed by pure tetracosane (С24H50 [C24]), octatetracontane (С48H98, [C48]) and their binary mixtures on a highly-oriented pyrolitic graphite (HOPG) were investigated by scanning tunneling microscopy (STM) and magnetic levitation tribometer (MLT)[2] methods. Pure C24 and C48 form smectic domain structure characterized by parallel lamellae. Whereas, STM-images of binary mixture C24/C48 indicate formation of nematic domain structure. MLT-experiments demonstrate the lowering of friction coefficient µ for such interfaces in contrast to pure C24 and C48 (Table 1). 
Table 1.  Kinetic friction coefficient μ for the steel ball and molecules of n-alkanes
n-alkane	Friction coefficient (μ)	
C24	0.48	
C48	0.81	
C48/C24	0.39	

1.	Marchenko A.,Cousty J., Pham Van L. Magic Length Effects in the Packing of n-Alkanes Adsorbed on Au(111) // Langmuir.-2002.-18.-P. 1711-1175.
2.	Vasko A., Braun O., Radzwill N., Marchenko O. et. al. Magnetic levitation tribometer: a point-contact friction // Tribol. Lett. -2018- 66: 74. https://doi.org/10.1007/s11249-018-1024-z