Rheo-NMR studies of a nematic worm-like micelle system in a high-shear-rate regime

Lepper, Chris; Edwards, Patrick J. B.; Dykstra, Robin; Williams, Martin A. K.

doi:10.1039/c1sm06126g

Cited by 6 publications

(4 citation statements)

References 40 publications

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“…35,78 However, we could not find comprehensive NMR studies at or below its phase transition. 36,104,105 While a change of alignment of PBLG and other LC phases in general has been shown previously under shear conditions, 4,10,13,14,49,80,88,92 we could show that spinning with rates above 20 Hz induces alignment even in PBLG/CDCl 3 samples at concentrations far below the LC transition. While dilution of the polymer component in the LC system seems to lead to a breakdown of intermolecular interactions in the static case, shearing of the sample seems to provide the statistical basis for close intermolecular contacts that are necessary for an aligned phase.…”

Section: Discussionsupporting

confidence: 72%

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Rheo-NMR at the Phase Transition of Liquid Crystalline Poly-γ-benzyl-l-glutamate: Phase Kinetics and a Valuable Tool for the Measurement of Residual Dipolar Couplings

Hoffmann,

Kouřil,

Berger

et al. 2023

Macromolecules

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Using a home-built rheo-NMR apparatus with Couette geometry that allows pulse program-controlled switching of spinning speeds, the formation of liquid crystalline phases of poly-γ-benzyl-l-glutamate (PBLG) in CDCl3 is studied at concentrations up to 15% (w/v) using deuterium NMR of the solvent under static and shear force conditions. A tilt of director alignment from 0 to ≈75–79° is observed. While the well-known first-order phase transition from isotropic to the liquid crystalline phase is detected in the static case, the transition vanishes under applied shear with freely scalable partial alignment down to the lowest concentrations measured. Close to the static phase transition concentration, a coexistence of isotropic and aligned phases is observed when a cosolute is added, which disappears upon application of shear forces. Temperature, concentration, and shear-rate-dependent alignment properties are characterized. In addition, kinetic studies involving the switching of shear forces reveal buildup rates for the phases in the range of milliseconds to minutes, which allowed the acquisition of an unaligned/aligned 2D correlation experiment in a favorable case. Finally, the usefulness of very low, rheo-induced alignment for the measurement of residual dipolar couplings is demonstrated.

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Section: Discussionsupporting

confidence: 72%

“…Spectra above 300 K lead to relatively broad lines, starting to show alignment tilt distributions due to the shear force distribution of the Couette geometry. In particular, at 313 K, the expected distribution pattern 88,89 becomes visible.…”

Section: Changing the Director Of Alignmentmentioning

confidence: 93%

Rheo-NMR at the Phase Transition of Liquid Crystalline Poly-γ-benzyl-l-glutamate: Phase Kinetics and a Valuable Tool for the Measurement of Residual Dipolar Couplings

Hoffmann,

Kouřil,

Berger

et al. 2023

Macromolecules

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show abstract

“…The usual Rheo-NMR experiment lacks a direct measure of shear stress although custom systems have been proposed that combine NMR and torque sensors [19,20], albeit still based on superconducting magnets with limited industrial application. Rheo-NMR has been applied to the study of many complex samples, including shear-banding materials [21][22][23], polymer solutions [24,25], worm-like micelles [26,27], liquid crystalline materials [19,[28][29][30][31], and colloidal particle suspensions [32,33]. Shear-induced migration of non-colloidal particles has been studied by NMR imaging in Couette [34][35][36] and pipe flow [37,38].…”

Section: Introductionmentioning

confidence: 99%

Validation of a low field Rheo-NMR instrument and application to shear-induced migration of suspended non-colloidal particles in Couette flow

Colbourne

Blythe

Barua

et al. 2018

Journal of Magnetic Resonance

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Nuclear magnetic resonance rheology (Rheo-NMR) is a valuable tool for studying the transport of suspended non-colloidal particles, important in many commercial processes. The Rheo-NMR imaging technique directly and quantitatively measures fluid displacement as a function of radial position. However, the high field magnets typically used in these experiments are unsuitable for the industrial environment and significantly hinder the measurement of shear stress. We introduce a low field Rheo-NMR instrument (H resonance frequency of 10.7MHz), which is portable and suitable as a process monitoring tool. This system is applied to the measurement of steady-state velocity profiles of a Newtonian carrier fluid suspending neutrally-buoyant non-colloidal particles at a range of concentrations. The large particle size (diameter >200μm) in the system studied requires a wide-gap Couette geometry and the local rheology was expected to be controlled by shear-induced particle migration. The low-field results are validated against high field Rheo-NMR measurements of consistent samples at matched shear rates. Additionally, it is demonstrated that existing models for particle migration fail to adequately describe the solid volume fractions measured in these systems, highlighting the need for improvement. The low field implementation of Rheo-NMR is complementary to shear stress rheology, such that the two techniques could be combined in a single instrument.

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“…For this purpose, in situ rheometric techniques have proliferated where a rheometer is coupled to other measurement devices to gain access to structural or dynamical information during flow. These in situ techniques include structural probes such as small angle scattering measurements [1][2][3][4][5] and particle tracking microscopy, [6][7][8][9] dynamical probes such as superposition rheometry, 9,10 nuclear magnetic resonance, 11,12 and Raman spectroscopy, 13,14 and techniques that afford both structure and dynamics such as X-ray photon correlation spectroscopy. 15,16 These in situ rheometric methods are all motivated by understanding how the imposition of shear forces influences the dynamic or structural response of that system.…”

Section: Introductionmentioning

confidence: 99%

Extracting microscopic insight from transient dielectric measurements during large amplitude oscillatory shear

Cho,

Shi,

Murphy

et al. 2023

Soft Matter

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Rheo-NMR studies of a nematic worm-like micelle system in a high-shear-rate regime

Cited by 6 publications

References 40 publications

Rheo-NMR at the Phase Transition of Liquid Crystalline Poly-γ-benzyl-l-glutamate: Phase Kinetics and a Valuable Tool for the Measurement of Residual Dipolar Couplings

Rheo-NMR at the Phase Transition of Liquid Crystalline Poly-γ-benzyl-l-glutamate: Phase Kinetics and a Valuable Tool for the Measurement of Residual Dipolar Couplings

Validation of a low field Rheo-NMR instrument and application to shear-induced migration of suspended non-colloidal particles in Couette flow

Extracting microscopic insight from transient dielectric measurements during large amplitude oscillatory shear

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