Abstract
In this review article, we discuss the rheological properties of the thermotropic smectic liquid crystal 8CB with focal conic domains (FCDs) from the viewpoint of structural rheology. It is known that the unbinding of the dislocation loops in the smectic phase drives the smectic-nematic transition. Here we discuss how the unbinding of the dislocation loops affects the evolution of the FCD size, linear and nonlinear rheological behaviors of the smectic phase. By studying the FCD formation from the perpendicularly oriented smectic layers, we also argue that dislocations play a key role in the structural development in layered systems. Furthermore, similarities in the rheological behavior between the FCDs in the smectic phase and the onion structures in the lyotropic lamellar phase suggest that these systems share a common physical origin for the elasticity.
Highlights
Rheology is a fundamental issue in soft matter science
It has been anticipated that such rheological behavior is influenced by defects [41,42], we have further shown in the previous section that these structures are focal conic domains (FCDs) which originate from dislocation loops
We argue the physical origin of the elasticity of the smectic phase with FCDs
Summary
Rheology is a fundamental issue in soft matter science. One of the most successful achievements in the rheology of soft matter is the Doi-Edwards model, which describes the viscoelastic response of Materials 2014, 7 entangled polymer melts [1]. The attempt to describe their universal rheological properties has only started using the concept of “soft glassy rheology” [5,6] Besides these glassy materials, the rheology of surfactant systems which exhibit the gyroid phase with a three-dimensional periodic structure, or the sponge phase with randomly connected bicontinuous interface remains unexplored except for some pioneered studies [7,8,9,10,11,12]. The rheology of surfactant systems which exhibit the gyroid phase with a three-dimensional periodic structure, or the sponge phase with randomly connected bicontinuous interface remains unexplored except for some pioneered studies [7,8,9,10,11,12] Their unique viscoelastic responses arise predominantly from deformation of meso-scale internal structures whose rearrangement can be induced under deformation or flow. In our experiment, reproducible results could be obtained by applying the pre-shear even without any anchoring treatment
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