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VOLUME 116 | ISSUE 4 | PAGE 251
Non-Newtonian rheology in twist-bend nematic liquid crystals
Abstract
In this work we present a simple qualitative model to describe shear rheological behavior of the twist-bend nematic liquid crystals (NTB). We find that at relatively low shear rate ({\dot \gamma } \leq {\dot 
\gamma}_{c1}) the stress tensor σ  created by this shear strain, scales as \sigma \propto 
{\dot \gamma }^{1/2}. Thus the effective viscosity decreases with the shear rate (\eta \propto {\dot \gamma }^{-1/2}) manifesting so-called shear-thinning phenomenon. At intermediate shear rate {\dot \gamma 
}_{c1} \leq {\dot \gamma} \leq {\dot \gamma }_{c2}, σ  is almost independent of {\dot \gamma } (a sort of plateau), and at large shear rate ({\dot \gamma } \geq 
{\dot \gamma}_{c2}), \sigma \propto {\dot \gamma }, and it looks like as Newtonian rheology. Within our theory the critical values of the shear rate scales as {\dot \gamma }_{c1}\propto ({\tilde {\eta 
}_2^0}/{\tilde {\eta }_3^0})^2, and {\dot \gamma}_{c2} \propto ({\tilde {\eta }_2^0}/{\tilde {\eta 
}_3^0})^4 respectively. Here {\tilde \eta }_2^0 and {\tilde \eta }_3^0 are bare coarse grained shear viscosity coefficients of the effective smectics equivalent to the NTB phase at large scales. The results of our work are in the agreement with recent experimental studies.