Elasticity of smectic liquid crystals with focal conic domains

Abstract

Abstract. We study the elastic properties of thermotropic smectic liquid crystals with focal conic domains (FCDs). After the application of the controlled preshear at different temperatures, we independently measured the shear modulus G ′ and the FCD size L. We find out that these quantities are related by the scaling relation G ′ ≈ γ eff /L where γ eff is the effective surface tension of the FCDs. The experimentally obtained value of γ eff shows the same scaling as the effective surface tension of the layered systems √ KB where K and B are the bending modulus and the layer compression modulus, respectively. The similarity of this scaling relation to that of the surfactant onion phase suggests an universal rheological behavior of the layered systems with defects.

Flow properties of a twist-bend nematic liquid crystal

“…, which is very different from the ‫ܩ‬ ᇱ (߱) ∝ ߱ ଶ , ‫ܩ‬ ᇱᇱ (߱) ∝ ߱ scaling with ω found in nematic and in uniform smectic LC phases with the shear plane along the layers. 31 The behavior is closer to that found in smectics with focal conic defects ‫ܩ(‬ ᇱ (߱) ∝ ߱ ଵ/ଶ , ‫ܩ‬ ᇱᇱ (߱) ∝ ߱ ଵ/ଶ ) 32 To find how the compression modulus of the pseudo-layers is related to θ, one needs to generalize the coarse-grained theory 34 20 , this extension should also include a complex interplay of domains of opposite chirality and domain walls separating them, so in general it is a complicated task. However, previous FFTEM studies on the same material showed that the width of the domain walls is typically less than 10 nm while the smallest distance between them is over 50 nm (see Figure 1 of Reference [27]); therefore, the domains with uniform heliconical twist director structure are much larger than the defect areas.…”

Structural Rheology of the Smectic Phase

“…In this section, we discuss the influence of FCDs on the linear viscoelasticity of the smectic phase [17]. We also argue the physical origin of the elasticity of the smectic phase with FCDs.…”

Structure formation of surfactant membranes under shear flow

“…An alternative experimental approach to gain insight into the structural changes is to characterize defects observed in the lamellar state for moderate shear rates, both in surfactant membranes 13,17 and in thermotropic liquid crystals. 18,19 It is also worth mentioning that stable cylindrical structures on a tenmicrometer length scale are observed when strong shear flow is applied in the lamellar-sponge coexistence state. 15 Several theoretical attempts have been made to tackle this complex problem of structural evolution under shear flow, which consider either instability of the lamellar phase due to undulations 20,21 or the break-up of droplets.…”