Probing molecular binding effect from zinc oxide nanocrystal doping in surface-stabilized ferroelectric liquid crystal with two-dimensional infrared correlation technique

Doping liquid crystal (LC) with nanomaterials has been shown to yield some degrees of freedom for tailoring LC properties. This approach can be employed to produce new LC materials with high application potentials by blending instead of synthesizing new mesogenic molecules: In this paper, we show that doping ferroelectric liquid crystal (FLC) with ZnO nanocrystals improves the alignment order of a surface-stabilized FLC (SSFLC) in both steady-state and field-induced reorientation processes. We used the two-dimensional infrared (2D IR) correlation technique to reveal that the ZnO nanocrystals were uniformly dispersed into the FLC medium. The homogeneous dispersion of ZnO nanodots produces stronger correlations among the IR-active molecular normal modes of FLC molecules, which then leads to more concerted reorientation process at the submolecular level. A molecular binding effect originating from a dipolar interaction of the ZnO nanodot with surrounding C=O groups of FLC molecules was proposed to illustrate our measured results. We estimated the total energy reduced by the doping to be about 1000 J/m(3). The alignment stability gained is similar to that experienced by FLC molecules within 100-nm distance to an alignment surface with a strong anchoring strength of 1 x 10(-4) J.m(-2).