[en] Highlights: • The effect of nanoparticles on the $R_{\mathit{II}}-R_I-R_V$ transitions is discussed. • The nanoparticles dependence of the transition tempearture is calculated. • The tricritical behavior of the $R_I-R_V$ transition is discussed. Experimental studies have shown that nanoparticles play an important role on the rotator phase transitions of n-alkanes. A phenomenological model for predicting the $R_{\mathit{II}}-R_I-R_V$ phase transitions in mixtures of alkanes and nanoparticles has been proposed by combining Flory-Huggins free energy of isotropic mixing and Landau free energy. The impact of nanoparticles on the $R_{\mathit{II}}-R_I-R_V$ phase transitions and their transition temperatures is discussed by means of phenomenological theory. The possibility of the tricritical behavior of the $R_I-R_V$ phase transition in the mixtures of alkanes and nanoparticles is discussed. The theoretical predictions are in good qualitative agreement with available experimental results.