Isotropic-liquid crystal phase equilibrium in semiflexible polymer solutions: effects of molecular weight and ionic strength in polyelectrolyte solutions

Inatomi, Shinichiro; Jinbo, Yuji; Sato, Takahiro; Teŕamoto, Akio

doi:10.1021/ma00045a030

Cited by 43 publications

(55 citation statements)

References 10 publications

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“…For samples with narrow molecular weight distribution (MWD) both c i and c a approach asymptotic values as the molecular weight of the xanthan becomes great enough to make the mean contour length L of the polymer equal to about one Kuhn length, which for wormlike chains is 2q. 16 The concentrations c i and c a are in the range of 0.1 g cm -3 at high C s and comparable to those characterizing the lyotropic phase diagrams of neutral rigid polymers. 17 As C s is reduced, both c i and c a decrease sigmoidally as electrostatic effects become prominent in the intermolecular potential.…”

Section: Introductionmentioning

confidence: 65%

“…Using a sample with molecular weight 2.35 × 10 5 , Milas and Rinaudo were the first to measure the steady shear viscosity of xanthan in 0.1 M aqueous NaCl into the biphasic and completely anisotropic domains, where they observed behavior similar to that of rodlike synthetic polymers. 14 Allain et al 67 carried out a similar, more extensive, 16 ). Phase separation results for X2F2 and X13F3 at 23°C (larger symbols) from Figure 3; the vertical dashed lines indicate the corresponding molecular weights of these samples.…”

Section: Introductionmentioning

confidence: 99%

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Rheology of Concentrated Isotropic and Anisotropic Xanthan Solutions. 1. A Rodlike Low Molecular Weight Sample

Lee

Brant

2002

Macromolecules

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The rheology of a rodlike xanthan sample (Fraction X13F3, Mw ) 1.54 × 10 5 g/mol) has been studied in aqueous NaCl (0.01, 0.1, 1.0 M) in oscillatory and steady shear experiments. Polymer concentrations W (in weight percent) spanning the isotropic, biphasic, and fully anisotropic regimes of the lyotropic liquid crystalline phase diagram have been investigated. The rheological parameters increase as power law functions of W in the isotropic regime, decrease with higher power law exponents in the biphasic regime, and change very slowly in the fully anisotropic regime. The peak in plots of steady shear viscosity η against W shifts toward lower W with increasing shear rate γ , because of the shearinduced orientation. In contrast, peaks in the plots of the complex viscosity η*, storage modulus G′, and loss modulus G′′ are independent of frequency ω, because shear-induced orientation is minimal under conditions of small strain. Power law curves fit to η*, G′, and G′′ in the isotropic, biphasic, and anisotropic regimes cross at W i and at Wa, the boundaries, respectively, between the isotropic and biphasic and between the biphasic and anisotropic regions as determined by phase separation measurements. No crossover of G′ and G′′ is observed for X13F3 at any salt concentration studied, and the loss tangent tan δ ) (G′′/G′) > 1 under all the conditions investigated. The parameters η* and G′′ conform to tight master curves when the appropriate reduced variables are plotted, but η and G′ do not. The Cox-Merz rule is obeyed at all three salt conditions for all polymer concentrations studied in the Newtonian plateau region of the reduced flow curves. The salt concentration plays an important role in determining W i and Wa for this ionic, rodlike polysaccharide, but it does not affect the Newtonian plateau viscosities in the isotropic regime. In contrast, the viscosities of anisotropic solutions at different salt concentrations increase as the salt concentration increases, because the order parameter in anisotropic solutions is greater at low salt concentration than it is at high salt concentration.

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Section: Introductionmentioning

confidence: 65%

Section: Introductionmentioning

confidence: 99%

Rheology of Concentrated Isotropic and Anisotropic Xanthan Solutions. 1. A Rodlike Low Molecular Weight Sample

Lee

Brant

2002

Macromolecules

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“…The axis ratio (L/d) and ionic strength are critical parameters in the degree of shear induced order, as well as for the relaxation behavior after shear ceases. [59,[82][83][84][85][86] Complementary to these investigations, Orts et al, [82] using SANS experiments, demonstrated the anisotropic shear ordering of cellulose microcrystals when studying black spruce bleached kraft pulp. Under shear these cellulose microcrystals showed an anisotropic alignment where the distance between the rods scales with C À1/2 at high concentrations.…”

Section: Optical and Orientation Propertiesmentioning

confidence: 91%

“…[91] These forces are governed by the axis ratio, the polydispersity in particle length, the surface charge density, the ionic strength, and the nature of the counter ions present in the whisker suspension. [59,[83][84][85]91] On the other hand, for perfect neutral rods with length L and diameter d, the critical concentration to display the ordered phase is only dependent on the axis ratio L/d, according to Onsager's theory. [92] However, for the charged rods, the electrostatic interactions play a key role in the phase separation.…”

Section: Polyelectrolytic Naturementioning

confidence: 99%

Rodlike Cellulose Microcrystals: Structure, Properties, and Applications

Lima¹,

Borsali²

2004

Macromol. Rapid Commun.

794

343

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Summary: In this article we present some interesting properties of rodlike cellulose microcrystals (so‐called “whiskers”). These microcrystals can be obtained from different cellulose sources such as wood, cotton, or animal origin. When submitted to acid hydrolysis, the cellulose fibers yield stable aqueous suspensions because of the presence of negative charges on the surface of the microcrystallites during the hydrolysis process. The obtained microcrystals are rod‐shaped particles, the dimensions of which depend on the cellulose origin. For instance, the cotton whiskers have typical dimensions varying from 100 to 300 nm in length, L, and 8 to 10 nm in diameter, d, while those of the tunicate whiskers range from 100 nm to few micrometers in length and 10 to 20 nm in diameter. At very low concentrations, these whiskers are randomly suspended in water and form an isotropic phase. When the concentration reaches a critical value, the whiskers spontaneously display ordered phases showing interesting liquid crystal properties (nematic and chiral nematic). The chiral nematic orders can be retained after evaporation of the solvent (generally water), leaving iridescent films. The reflected color can be controlled by changing either the ionic strength or by applying an electric field. These colloidal particles have been investigated using several techniques including small‐angle neutron scattering (SANS), small angle X‐ray scattering, rheology, and more recently dynamic and static light scattering techniques (DLS and SLS) to highlight their static and dynamic behavior. Because of their geometry, important axis ratio (L/d), and high crystallinity, these rods have been also extensively used to process nanocomposites based on polymer matrices, to reinforce their mechanical properties. All these properties are discussed in this contribution.Rodlike nanocrystals in aqueous suspension (left, Tunicate, 1 wt.‐%) and film (right), observed between cross‐polarizers.magnified imageRodlike nanocrystals in aqueous suspension (left, Tunicate, 1 wt.‐%) and film (right), observed between cross‐polarizers.

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“…The charge density o and the total salt concentration n together with geometrical parameters of the chains are supposed to be arbitrary parameters. The validity of our approach is based on the conditions (6), (9), (ll), (12), (13), (15). Among them the conditions (9), (ll), (15) are not very crucial: if they are not fulfilled, one should make the renormalizations (8) for o, n + nClj for n and (14) for persistent length 1.…”

Section: Lomentioning

confidence: 99%

Liquid‐crystalline ordering in solutions of polyelectrolytes

Nyrkova

Shusharina

Khokhlov

1997

Macro Theory & Simulations

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SUMMARYThe isotropic-nematic phase transition in solutions of stiff-chain polyelectrolytes is considered on the basis of the Onsager approach for the limiting cases of charged rods and persistent macrolecules. We plotted a full family of phase diagrams for orientational transitions in solutions of polyelectrolytes with any charge density as a function of the low-molecular-weight salt concentration. It is shown that charging of macromolecules can lead not only to the renormalization of the chain diameter (discussed by Onsager) or to the twisting effect (predicted by Odijk et al.), but in some cases also to a variety of other regimes, including transitions with very narrow phase separation regions, or with a second orientational transition to a highly oriented nematic phase upon the increase of polymer concentration.

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Isotropic-liquid crystal phase equilibrium in semiflexible polymer solutions: effects of molecular weight and ionic strength in polyelectrolyte solutions

Cited by 43 publications

References 10 publications

Rheology of Concentrated Isotropic and Anisotropic Xanthan Solutions. 1. A Rodlike Low Molecular Weight Sample

Rheology of Concentrated Isotropic and Anisotropic Xanthan Solutions. 1. A Rodlike Low Molecular Weight Sample

Rodlike Cellulose Microcrystals: Structure, Properties, and Applications

Liquid‐crystalline ordering in solutions of polyelectrolytes

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