XXIII Conference on Liquid Crystals Chemistry, Physics and Applications

Invited lecture - Effect of different surfactants on relaxation dynamics in confined liquid crystals

Broadband dielectric spectroscopy (BDS) can be used in the study of the influence of different surfactants on the dynamics of relaxation processes in numerous geometrically bounded mesophases. The influence of different types of surfactants (e.g. decanoic acid, lecithin and poly(isobutyl methacrylate) (PiBMA)) on the dynamics of relaxation processes was investigated in both nematic (NLC) and ferroelectric liquid crystal (FLC) subjected to various types of geometric constraints. Liquid crystals (LCs) were embedded in Synpor or Anopore porous membranes with surfactant modified inner surfaces. Additionally, the dispersion systems containing LCs doped with hydrophilic or hydrophobic aerosil nanoparticles were also investigated [1, 2].

In the Anopore membrane the decanoic acid and lecithin induce the homeotropic orientation of the NLC molecules on the walls of the cylindrical pores and observed corresponding relaxation processes are almost the same. BDS of lecithin treated Synpor membranes reveals the reorientation of the NLC molecules from planar to homeotropic on the complex multilayer structure present in their volume [3].

This paper presents the results concerning the influence of lecithin and PiBMA on the collective modes in FLC placed in Anopore membrane. Dielectric measurements suggest that when the pores in the Anopore membrane are covered with lecithin, a modified Goldstone mode seems to be observed, while in the case of PiBMA the Goldstone mode is removed from the dielectric spectrum. The observed effects were explained by taking into account the influence of surfactants on the orientation order of LC molecules on the pores surface.

 [1] A. Różański, Effect of hydrophobic aerosil nanoparticles on the dielectric properties of ferroelectric liquid crystal. Ferroelectrics 495, 53-59 (2016).

[2] A. Różański, Effective permittivity of liquid crystal nanodispersions and composites with different pore structure. Phase Transitions 92, 79-86 (2019).

[3]A. Różański, The molecular dynamics of nematic liquid crystal confined in porous membranes treated by different surfactants. Opto-Electronics Review 27, 339-344 (2019).