Molecular dynamics of 4-cyano-3-fluorophenyl 4-butylbenzoate (4CFPB) glass-forming liquid crystal in unidirectional silicon nanopores

Abstract

Complex dynamics of 4-cyano-3-fluorophenyl 4-butylbenzoate (4CFPB) in cylindrical non-intersecting nanopores, mean diameters 6 nm and 8 nm was studied by broadband dielectric spectroscopy. For relaxation processes ascribed to the flip-flop, reptation-like and collective motions, the short- and long-range time correlations were estimated and discussed. Size effect and differences in ordering of molecules in pores during cooling and heating runs were found. On cooling, vitrification occurred in pores, similarly as in bulk, while on heating two-step ordering of molecules along pore walls was evidenced by subsequent diminishing of ε″_max(T). Explanation based on data concerning solid state polymorphism of 4CFPB in bulk is given.

Keywords:

• molecular dynamics
• dielectric relaxation
• liquid crystals
• dynamics in nanopores

Acknowledgements

The authors would like to thank Dr Małgorzata Jasiurkowska-Delaporte for performing the measurements and Dr Wycliffe Kiprop Kipnusu for preparation of the porous matrices in Professor Kremer group at the Leipzig University.