Dislocations in uniaxial lamellar phases of liquid crystals, polymers and amphiphilic systems

TL;DR

This paper provides a comprehensive study of dislocations in lamellar phases of soft matter, combining experimental evidence and theoretical predictions to understand their properties, interactions, and effects on surface and bulk behaviors.

Contribution

It introduces new insights into dislocation surface interactions, fluctuation-induced interactions, and unbinding transitions in lamellar systems, supported by experimental and theoretical analysis.

Findings

Existence of screw and edge dislocations confirmed experimentally.

Surface deformations influence dislocation positions and interactions.

Dislocation unbinding transitions can occur under certain conditions.

Abstract

Dislocations in soft condensed matter systems such as lamellar systems of polymers, liquid crystals and ternary mixtures of oil, water and surfactant (amphiphilic systems) are described in the framework of continuum elastic theory. These systems are the subject of studies of physics, chemistry and biology. They also find applications in the industry. Here we will discuss in detail the influence of dislocations on the bulk and surface properties of these lamellar phases. Especially the latter properties have only been recently studied in detail. We will present the experimental evidence of the existence of screw and edge dislocations in the systems and study their static properties such as: energy, line tension and core structure. Next we will show how does the surface influence the equilibrium position of dislocations in the system. We will give the theoretical predictions and present the experimental results on thin copolymer films, free standing films of liquid crystals and smectic droplets shapes. The surface is deformed by dislocations. These deformations are known as edge profiles. Surface deformations induce elastic interactions between edge dislocations. A new phenonenon discussed in our paper is the fluctuations induced interactions between edge dislocations.At suitable conditions edge dislocations can undergo an unbinding transition. Also a single dislocation loop in a smectic freely suspended film can undergo an unbinding transition. We shall also compute the equilibrium size of the loop contained between two hard walls. Finally we will discuss the dynamical bulk properties of dislocations such as: mobility (climb and glide),permeation, and helical instability of screw dislocations. Lubrication theory will also be discussed.