Twist-grain boundary phase characterized by AFM technique

TL;DR

This study characterizes twist grain boundary phases in liquid crystalline systems using AFM, revealing nanoscale surface modulations linked to internal structural deformations.

Contribution

It provides the first detailed AFM analysis of surface relief in TGBC phases and proposes a model connecting surface features to internal block rotations.

Findings

AFM detected periodic surface relief of about 500 nm.

Surface displacement amplitude is a few nanometers.

Deformation varies with TGBC block orientation.

Abstract

Twist grain boundary (TGB) phases represent liquid crystalline systems with a regular array of defects. In our research, we studied a compound with a stable TGBC phase and established its structure by various experimental techniques. We observed the surface of the smectic film by AFM microscope and detected a periodic relief. We found that the displacement amplitude is few nanometers with the periodicity about 500 nm. Such periodicity is in accordance with the periodicity of the TGBC blocks rotation estimated by polarizing microscopy. The surface modulation is explained by the deformation of TGBC structure, which is created on TGBC films. A simplified model interpreting the observed smectic surface displacement to occur as a consequence of rotating TGBC blocks inside the sample is proposed. TGBC blocks deform differently depending on their orientation with respect to the force acting by the tip of AFM microscope cantilever probing the smectic surface.