Measurement of the full refractive index tensor in sheared liquid-crystalline polymer solutions

Hongladarom, K.; Burghardt, Wesley R.

doi:10.1021/ma00080a023

Cited by 46 publications

(42 citation statements)

References 8 publications

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“…As the system enters into the flow alignment regime, the orientation angle ψ 0 decreases to zero, yielding a fully symmetric scattering pattern. These results are in qualitative agreement with those obtained on tumbling LCPs by flow birefringence [319]. Using 2 H NMR-spectroscopy under shear, the flow-aligning properties of SDS/Dec calamitic phase prepared in D 2 O could be confirmed.…”

Section: Iv4 Director Orientations Under Shear : Scattering and Nmrsupporting

confidence: 88%

Shear-Induced Transitions and Instabilities in Surfactant Wormlike Micelles

Lerouge

Berret

2009

Polymer Characterization

147

153

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In this review, we report recent developments on the shear-induced transitions and instabilities found in surfactant wormlike micelles. The survey focuses on the nonlinear shear rheology and covers a broad range of surfactant concentrations, from the dilute to the liquid-crystalline states and including the semidilute and concentrated regimes. Based on a systematic analysis of many surfactant systems, the present approach aims to identify the essential features of the transitions. It is suggested that these features define classes of behaviors. The review describes three types of transitions and/or instabilities: the shear-thickening found in the dilute regime, the shear-banding which is linked in some systems to the isotropic-tonematic transition, and the flow-aligning and tumbling instabilities characteristic of nematic structures. In these three classes of behaviors, the shear-induced transitions are the result of a coupling between the internal structure of the fluid and the flow, resulting in a new mesoscopic organization under shear. This survey finally highlights the potential use of wormlike micelles as model systems for complex fluids and for applications.

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Section: Iv4 Director Orientations Under Shear : Scattering and Nmrsupporting

confidence: 88%

Shear-Induced Transitions and Instabilities in Surfactant Wormlike Micelles

Lerouge

Berret

2009

Polymer Characterization

147

153

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“…3, 47 As we move to increasingly complex shear/extensional flows in which the scattering pattern reflects contributions from the whole slit flow thickness, the implicit assumption of a macroscopically uniaxial orientation state is fully compromised. Indeed, we observe bimodal distributions of orientation in slit-expansion flows 25 for which an orientation parameter analysis is wholly inappropriate (Fig.…”

Section: Methodsmentioning

confidence: 99%

X-ray scattering studies of orientation in channel flows of a thermotropic liquid-crystalline polymer

Cinader

Burghardt

1999

J. Polym. Sci. B Polym. Phys.

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In situ wide‐angle X‐ray scattering (WAXS) orientation measurements are reported for a commercial thermotropic copolyester melt in channel flows. This investigation includes extensive examination of the orientation effects of mixed shear‐extensional kinematics produced by channel flows with varying cross sections. Extensional gradients in a slit‐contraction flow produce large increases in orientation, similar to those seen in lyotropes. In sharp slit‐expansion flow, a bimodal orientation state is observed in which one population is aligned in the downstream direction while the other lies perpendicular to the expected local streamlines. This is attributed to stretching transverse to the flow direction in expansion regions. Weaker extensional gradients in a gradual expansion lead to a smaller effect. Flow along the centerline upstream and downstream of an obstruction leads to behavior similar to that observed in expansions and contractions, while flow around a sharp 90° bend produces orientation that tracks the expected streamlines, without significant change in the degree of orientation. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3411–3428, 1999

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“…It may be used in either steady or oscillatory shear flow, but due to refraction at the air-window interfaces, the maximum angle |θ| within the shear flow field is around 30°. In this flow cell, significant refraction at the air-window and window-fluid interfaces also introduces polarization effects that may be accounted for using Fresnel refraction coefficients; full equations are given in ref 40. The second flow cell is described by Brown and co-workers, 41 and provides linear shear flow between two prisms with faces cut to allow light to pass through the shear flow at θ ) 30°and 60°without suffering refraction effects.…”

Section: Flow Cellsmentioning

confidence: 99%

Steady and Oscillatory Shear Flow Alignment Dynamics in a Lamellar Diblock Copolymer Solution

Zryd

Burghardt

1998

Macromolecules

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Shear flow alignment in a symmetric polystyrene-polyisoprene (PS-PI) diblock copolymer solution in dioctyl phthalate has been studied using flow birefringence and rheology. In large amplitude oscillatory shear, we find behavior similar to that previously reported in lamellar PS-PI melts. At high reduced frequency, parallel alignment of the layers is preferred, confirmed with birefringence measurements using oblique light paths. At low reduced frequency, perpendicular alignment is favored. In steady shear flow experiments well below the ODT, a similar behavior pattern is found: perpendicular alignment results at low shear rates, and parallel alignment is found at high shear rates. These are the first results demonstrating flipping by a change in steady shear flow conditions. As temperature is increased, the degree of perpendicular alignment obtained at low reduced shear rates decreases, unlike the behavior in large amplitude oscillatory flow, where high degrees of perpendicular alignment are achieved at low frequencies even close to the ODT. This suggests that flow alignment in steady shear is more complex than that in oscillatory shear flow, perhaps owing to an increased likelihood for defect formation. Finally, no flow-induced changes were observed in the order-disorder transition in either steady or large amplitude oscillatory shear flow.

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Measurement of the full refractive index tensor in sheared liquid-crystalline polymer solutions

Cited by 46 publications

References 8 publications

Shear-Induced Transitions and Instabilities in Surfactant Wormlike Micelles

Shear-Induced Transitions and Instabilities in Surfactant Wormlike Micelles

X-ray scattering studies of orientation in channel flows of a thermotropic liquid-crystalline polymer

Steady and Oscillatory Shear Flow Alignment Dynamics in a Lamellar Diblock Copolymer Solution

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