Enhanced Frank elasticity and storage modulus in a diamagnetic liquid crystalline ferrogel

Bhargavi, R.; Nair, Geetha G.; Prasad, S. Krishna; Kumar, Nitesh; Sundaresan, A.

doi:10.1039/c1sm05986f

Cited by 8 publications

(12 citation statements)

References 27 publications

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“…In a previous work [18] we have found that the addition of HSA molecules to the LC system can increase the short-range correlation (of the smectic type) in the nematic phase. The shortrange smecticity can be expected to affect the reorientation properties of the aligned nematic structure.…”

Section: X-ray Diffraction Studiesmentioning

confidence: 87%

“…This is observed in materials exhibiting thermally-driven sol-gel transitions, where both the sol and the gel have anisotropic nematic characteristics. [18] Since the sol nematic phase behaves similar to that of a standard fluid with G' < G'', the sol-gel transition can easily be identified by monitoring the thermal variation of the elastic moduli. Figure 4 presents the temperature dependence of the two elastic moduli (G' and G'') for the pure NLC and the three composites, G 1 , G 2 , and G 10 .…”

Section: Rheological Characterisationmentioning

confidence: 99%

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Anchoring Transition Induced by Gelation in a Liquid Crystal System

2012

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We report a novel type of anchoring transition (ANT) in a liquid crystal driven by the physical gelation of the system. The ANT manifests as anomaly in the thermal behaviour of the dielectric permittivity. Data from X-ray studies suggest that ANT is caused by the ability of the gel fibres to compete with the substrate-driven orientation conditions. It is further found that the molecular reorientation is possible only in cases where the gel is weak, the difference between weak and strong gels being established by rheological measurements.

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Section: X-ray Diffraction Studiesmentioning

confidence: 87%

Section: Rheological Characterisationmentioning

confidence: 99%

Anchoring Transition Induced by Gelation in a Liquid Crystal System

2012

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“…12-Hydroxystearic acid (HSA for short), commercially available from Sigma-Aldrich, was used as the gelator. HSA is known to gelate a wide variety of organic solvents and liquid crystals. , The chemical structures of the RLC, BLC, and the gelator are shown in Figure . From our previous study with a similar RLC host, it is known that the gel viscosity and mechanical strength are moderate for low concentrations of HSA.…”

Section: Methodsmentioning

confidence: 99%

“…The gels composed of the calamitic or the rodlike variety of LCs have been quite well studied, and a number of interesting results have emerged. Notable among the features seen for the gels in comparison with the corresponding nematic sol state are faster electro-optic response, − flexible displays, exceptionally large Frank elastic constant, high electromechanical response, rewritable patterning, bistable nematic states, molecular conductivity, enhanced hole mobility, stabilization of the magnetic nanoparticle dispersion, and high electrical conductivity . Such gels have also been found quite interesting for their viscoelastic behavior exhibiting soft-glass rheological features .…”

Section: Introductionmentioning

confidence: 99%

Diminished Splay Stiffening in Weak Gels of Calamitic–Bent-Core Nematic Composites

et al. 2016

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Composites of calamitic and bent-core nematic molecules exhibiting a nematic to nematic-gel transformation have been investigated using thermal, electrical, X-ray, and mechanical probes. The studies focusing on the Frank elastic behavior show a surprising result that the thermal behavior of the threshold voltage and the dependent splay elastic constant (K11) are remarkably different in temperature regions identified as weak and strong gels. In the former gel, the parameters exhibit values significantly smaller than the higher-temperature fluid nematic, effectively canceling out the underlying thermal variation due to the order parameter. This is especially attractive from the viewpoint of display devices. The X-ray diffraction data suggest that the fibers have a plastic nature in the weak gel and 3D-crystalline ordering in the strong gel. We argue that the different elastic behavior in the two gel phases is caused by the nature of the fibers; they are stiff in both gels but the interfiber interaction is weaker in the weak gel allowing the splay elastic constant to be lowered. The X-ray and rheological data lend support to the characterization of the fibers.

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“…19 The rheological properties of ferrofluids in magnetic fields have been studied in detail, [19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] however, the rheological properties of magnetic soft materials have received little attention. For example, incorporation of small amounts of magnetite nanoparticles in a lyotropic polymer liquid crystalline matrix (a ferronematic) 36 and in a liquid crystalline ferrogel 37 resulted in an enhanced viscosity. In ferrogels, the rheological properties are potentially interesting due to the elastic nature of the gel matrix.…”

Section: Introductionmentioning

confidence: 99%

Enhanced rheological properties of dilute suspensions of magnetic nanoparticles in a concentrated amphiphilic surfactant solution

Santiago-Quiñonez

Rinaldi

2012

Soft Matter

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We present an experimental study of the magnetorheological response of dilute suspensions of magnetic nanoparticles in concentrated amphiphilic surfactant solutions. Low particle content (<0.4% v/v) induced significant increase in viscosity, enhancing the shear thinning behavior observed in the absence of the nanoparticles. A magnetic field induced yield stress of up to 10 Pa at magnetic fields of up to 0.4 T was also observed. Experiments under small amplitude oscillatory shear indicate a transition from viscous to elastic behavior at a critical magnetic field which depends on the frequency of the oscillatory shear. At low applied magnetic fields loss and storage moduli are independent of the magnetic field and increase with the frequency of the oscillatory shear. At high applied magnetic fields both the loss and storage moduli seem to asymptote to a power law dependence on the magnetic field magnitude. These results illustrate the possibility of inducing dramatic changes in the rheological properties of complex fluids by addition of minute amounts of magnetic nanoparticles and application of magnetic fields.

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Enhanced Frank elasticity and storage modulus in a diamagnetic liquid crystalline ferrogel

Cited by 8 publications

References 27 publications

Anchoring Transition Induced by Gelation in a Liquid Crystal System

Anchoring Transition Induced by Gelation in a Liquid Crystal System

Diminished Splay Stiffening in Weak Gels of Calamitic–Bent-Core Nematic Composites

Enhanced rheological properties of dilute suspensions of magnetic nanoparticles in a concentrated amphiphilic surfactant solution

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