J. Ananthaiah

University of Hyderabad, Bhaganagar, Andhra Pradesh, India

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Publications (7)11.97 Total impact

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    ABSTRACT: We report studies on the rheological properties of a liquid crystalline analog of Abrikosov phase in type-II superconductors known as twist-grain-boundary-A (TGB_{A}) phase. The TGB_{A} phase shows a large apparent yield stress compared to the cholesteric (N^{*}) phase. The storage modulus (G^{^{'}}) of the TGB_{A} phase is significantly larger than the loss modulus (G^{^{''}}). The dynamic relaxation measurements indicate a solid-like behavior of N^{*}, TGB_{A}, and smectic-C^{*} phases. The complex shear modulus of the TGB_{A} phase exhibits a power-law behavior G^{*}(ω) ∼ ω^{α} with α≃0.5. The relative amplitude of G^{^{'}} and G^{^{''}} at various temperatures indicate that the enhanced elasticity of TGB_{A} phase is due to the structural defects.
    Physical Review E 07/2014; 90(1-1):012506. · 2.31 Impact Factor
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    ABSTRACT: We report experimental studies on the rheology of a few nematic liquid crystals with highly polar molecules (CCH-7, PCH-7, CB-7). The selected molecules have the same alkyl chain (-C_{7}H_{15}) and cyano (-CN) end group. In the core part of the molecule, CCH-7 has two cyclohexane rings, PCH-7 has one cyclohexane and one aromatic ring, and CB-7 has two aromatic rings. Two viscosities were measured as a function of temperature, namely, η_{2} (director parallel to the shear direction) and η_{1} (director perpendicular to the shear direction). The orientation of the director was studied using small angle light scattering techniques. η_{2} was measured in presheared sample, whereas the electrorheological technique was used to measure η_{1}. We show that both viscosities of the liquid crystals depend on the number of aromatic rings and Kirkwood correlation factor. The temperature dependent viscosities can be understood based on the intramolecular π-electron conjugation and intermolecular association of highly polar molecules.
    Physical Review E 02/2014; 89(2-1):022510. · 2.31 Impact Factor
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    ABSTRACT: We report the measurements of active and passive viscosities of a bent-core nematic liquid crystal. The active viscosity is measured using a rheometer and the passive viscosities are measured by measuring the self-diffusion coefficient of a microsphere in the aligned sample. The effective active viscosity is larger and the effect of presmectic fluctuations are observed much higher than the N–Sm-C transition temperature than commonly seen in calamitic liquid crystals. The temperature dependence of passive viscosities is stronger than that of active viscosities. The self-diffusion of the microsphere is reduced and appears to be non-Gaussian as the N–Sm-C transition is approached. The study of Brownian fluctuations is useful to understand the smectic fluctuations in bent-core nematic liquid crystals.
    Physical Review E 03/2013; 87:030501. · 2.31 Impact Factor
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    ABSTRACT: We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (NR) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-NR phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-NR phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density.
    Physical Review E 07/2012; 86:011710. · 2.31 Impact Factor
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    ABSTRACT: We report experimental studies on small-angle light scattering (SALS), rheodielectric and elec- trorheological properties of a binary mixture of octyloxy cyanobiphenyl (8OCB) and hexyloxy cyanobiphenyl (6OCB) liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA), and then again to a re-entrant nematic (NR ) phase transitions. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from rheo-SALS experiments is attributed to the realignment of director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of effective viscosity and static dielectric constant, reveals the changes in the director orientation across N-SmA-NR phase transi- tions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-NR phase transitions in the intermediate field range. Shear modulus of the SmA phase in the intermediate field range is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density.
    Physical Review E (Submitted). 02/2012;
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    ABSTRACT: We report simultaneous measurements of shear viscosity (η) and dielectric constant (ε) of octyloxy cyanobiphenyl (8OCB) in the nematic (N) and smectic-A (SmA) phases as functions of temperature and electric field. With increasing electric field η increases in the N phase whereas it decreases in the SmA phase and saturates beyond a particular field in both the phases. The flow curves in the intermediate-field range show two Newtonian regimes in the N phase. The temperature-dependent behavior of η and ε at zero or at small electric field suggests the occurrence of several structures that results from precessional motion of the director along the neutral direction as reported in similar other system. We show that the precessional motions are gradually suppressed with increasing electric field and the effective viscosity resembles with the Miesowicz viscosity η1 at high enough electric field. In the intermediate field range the temperature-dependent η exhibits anomalous behavior across the N-SmA phase transition which is attributed to the large contribution of Leslie coefficient α1.
    The European Physical Journal E 08/2011; 34(8):74. · 2.18 Impact Factor
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    ABSTRACT: We measured rheological properties of cholesteryl nonanoate and its mixture with 40-octyloxy-4-cyanobiphenyl. In both systems, wider temperature range of blue phase under shear with anomalous increase in viscosity associated with non- Newtonian flow behavior has been observed. Shear thinning followed by Newtonian flow is found in cholesteric phase and non-Newtonian flow behavior at high shear rates is seen in smectic-A phase. In cholesteryl nonanoate a small peak in the viscosity at cholesteric to smectic-A transition along with a shear rate dependent viscosity at higher shear rate is attributed to the type-II character of the compound. We find that the type-II character of the compound is further enhanced by mixing a small amount (20 wt%) of 40-octyloxy-4-cyanobiphenyl in cholesteryl nonanoate. No significant change in the temperature dependent rheological behavior is observed at the twistgrain- boundary-A to smectic-A transition. It is suggested that the small anomalous peak in the viscosity just above the twist-grain-boundary-A phase is due the existence of chiral line liquid phase.
    Molecular Crystals and Liquid Crystals 06/2011; 547:39-45. · 0.53 Impact Factor