Smectic rheology close to the smectic-nematic transition

Abstract

PACS 47.57.Qk-Complex fluids and colloidal systems: Rheological aspects PACS 64.70.mj-Experimental studies of liquid crystal transitions PACS 61.30.Jf-Defects in liquid crystals Abstract-We study the rheological properties of a thermotropic liquid crystal, 8CB, in the smectic phase close to the smectic-nematic (Sm-N) transition temperature. Three different regimes were identified in the flow curves at different temperatures: i) appearance of the yield stress at low stresses, ii) power law behavior at intermediate shear stresses, and iii) Newtonian at higher shear stresses. The vanishing of the yield stress at the Sm-N transition temperature is correlated with a rapid growth of focal conic domains. The constructed dynamic phase diagram exhibits the two different smectic phases together with the flow-induced Sm-N transition.

Structural rheology of composite onion phase

“…In the introduction, three possibilities on the shear-thickening, buckling of the layers, change of the layer orientation, and rearrangement of the layer conformation, were referred. Among three possibilities, the lamellar orientation from parallel to perpendicular one will not contribute to the increase of the viscosity because in the perpendicularly oriented layers one can detect only in-plane viscosity which shows very low viscosity [39]. As we showed in the scaling behavior of the shear modulus, the lamellar phase in this study is occupied by defects.…”

Orientation transition of defective lyotropic triblock copolymer lamellar phase

“…One is a shear-induced onion phase reported for many kinds of lyotropic lamellar phases [1][2][3][4][5]9]. The other is layer orientation transition from c to a-orientation, which is generally appeared at high shear rate region [1,[3][4][5]12]. Here, a-orientation corresponds to perpendicular orientation, where the layer normal is parallel to the neutral direction (n).…”

“…Layered systems such as amphiphilic lamellar phases and thermotropic smectic phases often show fascinating nonequilibrium phase transition under shear [1][2][3][4][5][6][7][8][9][10][11][12]. Weak shear flow usually aligns layers in c-orientation, where the layer normal is parallel to the velocity gradient (∇v) direction (see Fig.…”

Kinetics of the orientation transition in the lyotropic lamellar phase

“…rheology of the lamellar phase has many open issues such as a defect-mediated shear-thinning behavior, the origin of the elasticity, and the non-equilibrium structural transition induced by shear [1][2][3][4][5][6][7][8][9][10][11]. especially the nonequilibrium structural transition has been extensively studied both experimentally and theoretically for more than two decades.…”

“…One is a thermodynamically stable multilamellar vesicle (mLV) phase formation under shear flow [1][2][3][4][5]. And another one is an orientation transition of the lamellae from parallel to perpendicular orientation [5][6][7][12][13][14][15][16][17]. Since there are many reports on the orientation transition for many systems such as thermotropic smectic phase, amphiphilic lamellar phase, and block copolymer melt [18][19][20][21], the orientation transition is likely to be an universal structural transition in the layered system.…”