Effect of superhydrophobic nanoplatelets on the phase behaviour of liquid crystals

We investigate the effect of superhydrophobic Perfluorinated Silica Nanoplatelets (PFSNP) on the Isotropic-Nematic-Smectic-A-Smectic-C phase transitions of the liquid crystalline compound 4-n-pentyloxyphenyl-4'-n-octyloxybenzoate by means of polarised optical microscopy, differential scanning calorimetry, x-ray scattering, and birefringence measurements. We measure the phase transition temperature shift, coexistence temperature span variation, and the orientational order parameter of the nanocomposites, as functions of the mass fraction of nanoplatelets. These variations are non-monotonic function of PFSNP mass fraction and they are definitely related among them with linear laws. We show that the non-monotony may be related with PFSNP dispersion quality, partial-aggregation phenomena of PFSNP, and/or to nanoplatelet organization. The isotropic-nematic transition becomes softer in presence of the nanoplatelets. Nematic and smectic-C phase temperature span is practically independent from the PFSNP volume fraction. In contrary, the smectic-A phase is further stabilized for its temperature window becomes much wider in the presence of the PFSNP. A phenomenological model accounts for the experimental observations. (C) 2019 Elsevier B.V. All rights reserved.