The Shear-Flow Properties of Liquid Crystals

Larson, Ronald G.; Mather, Patrick T.

doi:10.1007/978-94-011-5480-2_11

Cited by 4 publications

(10 citation statements)

References 35 publications

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“…(v) As the sample is continuously sheared, regions which had initially become homeotropic display the onset of a square grid like defect structure. A similar type of shear induced defect structure has been seen by Larson et al [5] in a thermotropic liquid crystal. This is due to disruption of the monodomains in the form of undulation instabilities [13].…”

Section: Defect Structure Of the Lamellar Phase And Its Evolutisupporting

confidence: 78%

“…Since the observed rheometric properties of lamellar phases (for some recent studies see [4][5][6]) are presumably a consequence of topological defects and textures, one must first correlate the rheometry to direct visual observations. One could then hope to build a theory in two stages, by explaining first how the defects produce the rheology, and second why flow or sample preparation produces the defects to begin with.…”

Section: Introduction and Resultsmentioning

confidence: 99%

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Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases

et al. 1999

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We present important new results from light-microscopy and rheometry on a moderately concentrated lyotropic smectic, with and without particulate additives. Shear-treatment aligns the phase rapidly, except for a striking network of oily-streak defects, which anneals out much more slowly. If spherical particles several microns in diameter are dispersed in the lamellar medium, part of the defect network persists under shear-treatment, its nodes anchored on the particles. The sample as prepared has substantial storage and loss moduli, both of which decrease steadily under shear-treatment. Adding particles enhances the moduli and retards their decay under shear. The data for the frequency-dependent storage modulus after various durations of sheartreatment can be scaled to collapse onto a single curve. The elasticity and dissipation in these samples thus arises mainly from the defect network, not directly from the smectic elasticity and hydrodynamics.

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Section: Defect Structure Of the Lamellar Phase And Its Evolutisupporting

confidence: 78%

Section: Introduction and Resultsmentioning

confidence: 99%

Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases

et al. 1999

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“…In particular, we analyzed data based on long concatemers of λ-phage DNA, in particular 7-λ-DNA, stretching in microfluidic devices obtained using single molecule fluorescence microscopy. 8 We calculated the work done by the fluid on the polymer by considering the hydrodynamic drag forces using the Zimm model and slender body theory 5,37 - with no adjustable parameters (see Methods). Using this approach, we calculated the work required to stretch a polymer from the coiled state to a predefined final extension based on single molecule stretching trajectories in planar extensional flow.…”

Section: Resultsmentioning

confidence: 99%

“…Here, we also used the relationship for ideal linear chains such that the radius of gyration

R_{g} = {false〈 λ^{2} false〉}^{1 / 2} / \sqrt{6}

is related to the mean-squared end-to-end distance 〈λ 2 〉. 5 In the coiled state, we calculated ζ using scaling arguments and center-of-mass diffusion coefficients from prior single molecule experiments on long DNA molecules. 11 We determined ζ = 0.0031 pN·s/µm at a solution viscosity η s = 8.4 cP, conditions under which the transient stretching data was obtained.…”

Section: Methodsmentioning

confidence: 99%

“…Alternatively, polymer chains can be stretched and oriented far from equilibrium using hydrodynamic flow, 5–7 and well-defined fluid flows are easily generated in microfluidic devices. 8–10 In this way, coupling single molecule fluorescence microscopy with microfluidics allows for direct observation of polymer dynamics in equilibrium and nonequilibrium conditions.…”

Section: Introductionmentioning

confidence: 99%

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Determining elasticity from single polymer dynamics

Latinwo

Schroeder

2014

Soft Matter

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The ability to determine polymer elasticity and force-extension relations from polymer dynamics in flow has been challenging, mainly due to difficulties in relating equilibrium properties such as free energy to far-from-equilibrium processes. In this work, we determine polymer elasticity from the dynamic properties of polymer chains in fluid flow using recent advances in statistical mechanics. In this way, we obtain the force-extension relation for DNA from single molecule measurements of polymer dynamics in flow without the need for optical tweezers or bead tethers. We further employ simulations to demonstrate the practicality and applicability of this approach to the dynamics of complex fluids. We investigate the effects of flow type on this analysis method, and we develop scaling laws to relate the work relation to bulk polymer viscometric functions. Taken together, our results show that nonequilibrium work relations can play a key role in the analysis of soft material dynamics.

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Model systems for single molecule polymer dynamics

Latinwo

Schroeder

2011

Soft Matter

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Double stranded DNA (dsDNA) has long served as a model system for single molecule polymer dynamics. However, dsDNA is a semiflexible polymer, and the structural rigidity of the DNA double helix gives rise to local molecular properties and chain dynamics that differ from flexible chains, including synthetic organic polymers. Recently, we developed single stranded DNA (ssDNA) as a new model system for single molecule studies of flexible polymer chains. In this work, we discuss model polymer systems in the context of “ideal” and “real” chain behavior considering thermal blobs, tension blobs, hydrodynamic drag and force–extension relations. In addition, we present monomer aspect ratio as a key parameter describing chain conformation and dynamics, and we derive dynamical scaling relations in terms of this molecular-level parameter. We show that asymmetric Kuhn segments can suppress monomer–monomer interactions, thereby altering global chain dynamics. Finally, we discuss ssDNA in the context of a new model system for single molecule polymer dynamics. Overall, we anticipate that future single polymer studies of flexible chains will reveal new insight into the dynamic behavior of “real” polymers, which will highlight the importance of molecular individualism and the prevalence of non-linear phenomena.

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The Shear-Flow Properties of Liquid Crystals

Cited by 4 publications

References 35 publications

Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases

Structure and rheology of the defect-gel states of pure and particle-dispersed lyotropic lamellar phases

Determining elasticity from single polymer dynamics

Model systems for single molecule polymer dynamics

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