Effect of Alkyl Chain Length on the Orientational Behavior of Liquid Crystals Nano-Film

Different homologues of cyanobiphenyl liquid crystals (CB LC) (nCB with n = 5, 6, 7) present an interesting and novel material system. So far, their orientational behavior at nanoscale has not been extensively investigated yet. Here, we utilized a self-established in situ ball-on-disk testing platform equipped with polarized Raman spectroscopy, to study the ordering performance of nCB LCs confined as a nano-thin lubricating film. The results demonstrated that both external condition as shear velocity and internal molecular alkyl length dramatically affect the ordering process of nCB LC nano-lubricating film, consequently the degree of anisotropy. A simple model, along with detailed physical analysis, has been proposed to explain the observed phenomena. Our findings may provide new insights into controlling the alignment of LCs during lubricating.