Comparison of the Rheological Properties of Concentrated Solutions of a Rodlike and a Flexible Chain Polyamide

Baird, Donald G.; Ballman, R. L.

doi:10.1122/1.549530

Cited by 57 publications

(20 citation statements)

References 6 publications

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“…A second way of superpositioning the viscosity data is by plotting qsp vs cMw (Baird and Ballman 1979). In this case a shape assumption is no longer available and only molecules with the same approximate shape and conformation will superimpose.…”

Section: Qsp Versus Cmwmentioning

confidence: 99%

Comparison of the Conformation of Tomato Pectins With Apple and Citrus Pectins

Kokini¹,

Chou²

1993

Journal of Texture Studies

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7'he conformation of hot break tomato pectins in water/glycerol solutions as afinction of degree esteriflcation was studied and compared with the conformation of apple and citrus pectin using reduced storage [GYR and loss [G'YR moduli and the theories of Marvin and McKinney for rod-like behavior and those of Rouse as well as Zimm for random coil conformation. In all three cases the theory of Zimm implying dominant hydrodynamic interactions p t the experimenal data best. This is consistent with current knowledge on chemical structure of pectin where the charged uronides clearly readily interact with each other. 0 Copyright 1593 by Food & Nutrition Press, Inc.. Trumbull, Connecticut. 117 118 J.L. KOIUNI and T.C. CHOU et al. 1973). They can undergo deesterification and depolymerization in aqueous solution. The pH of greatest stability is around 4 (Smith and Bryant 1968; Pedersen 1980; BeMiller and Whistler 1958).Several factors affect the rheological properties of pectins in solution. These are electrolyte concentration, molecular weight, the degree of esterification, and the pH (Nelson el al. 1977). Paoletti et af. (1986) hypothesized that monovalent cation salts of pectins are highly ionized in solution, and the distribution of ionic charges along the molecule tends to keep it in an extended form. Ionization also prevents aggregation between the polymer chains resulting in solutions of stable viscosity because each polymer chain is hydrated, extended and independent (BeMiller and Whistler 1958). However, Thibault and Rinaudo (1986) found that monovalent cations caused a decrease in viscosity, the degree of which was greater with decreasing DE. Addition of salts of di-and tri-valent cations had the op posite effect.Tomato pectic substances extracted according to their solubility in water, 0.2% ammonium oxalate, 0.05N hydrochloric acid and 0.05N sodium hydroxide were found to be highly polydisperse, with the majority having a molecular weight of 2 X lo5 using gel filtration (Stein and Brown 1975) . Luh et af. (1984) found that the weight average molecular weights of pectinic acids isolated from fresh tomatoes of six cultures ranged from 7870-26,800. This calculation was based on measurement of intrinsic viscosity and Mark-Houwink constants obtained by Owens et al. (1946). The Mark-Houwink exponents were in the range of 1.38-1.42. If the assumption of random coil type molecule was made, the molecular weights would be larger approximately by a power of 1.5, since the Owens approximation uses a Mark-Houwink exponent of 1.38 and a random coil molecule would have an exponent between 0.8-0.9 (Luh et al. 1984). In that case the weight average molecular weights would range from approximately 7 x lo5 to 5 x lo6. These values would then be consistent with those obtained by Stein and Brown (1975).Fishman et al. (1984) showed that the radii of gyration of pectin molecules were significantly affected by the degree of methylation, with 57% being an o p timal value where steric hindrance would prevent further aggregation. Pippen e...

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Section: Qsp Versus Cmwmentioning

confidence: 99%

Comparison of the Conformation of Tomato Pectins With Apple and Citrus Pectins

Kokini¹,

Chou²

1993

Journal of Texture Studies

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“…Doi and Edwards15, 16 predicted the zero shear viscosity of rigid rods in concentrated solution or in melt scales with the sixth power of molecular weight, whereas that of most flexible linear polymers increases typically with the 3.4 power of molecular weight 17. Experimental results of such high power ranging from M 4 to M 7 have been reported for both lyotropic18, 19 and thermotropic20–22 liquid crystalline polymers. Although the magnitude of the power should reflect the stiffness of the polymer, the uncertainty in the literature values estimated with a limited range of molecular weights could be large because of experimental errors in both molecular weight and zero shear melt viscosity measurements.…”

Section: Introductionmentioning

confidence: 96%

Molecular dimensions and melt rheology of an all‐aromatic liquid crystalline polymer

Seo

Caflisch

2001

J Polym Sci B Polym Phys

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The molecular dimensions and melt rheology of a thermotropic all-aromatic liquid crystalline polyester (TLCP) composed of p-hydroxy benzoic acid, hydroquinone, terephthalic acid, and 2,4-naphthalenedicarboxylic acid is examined. The Mark-Houwink exponent (␣) of 0.95 is estimated for the TLCP. The persistence length estimated from molecular weight (M) and intrinsic viscosity ([]) data using the Bohdanecky-Bushin equation is about 95 Å, whereas that estimated from light scattering data is 117 Å. These persistence lengths and the observed ␣ value, both higher than those for flexible polymers, suggest that the present TLCP is a semirigid polymer. The zero shear melt viscosity ( 0 ) varies with approximately M 6 for molecular weight M Ͼ 3 ϫ 10 4 g/mol; below this molecular weight, 0 varies almost linearly with M. Widely different entanglement molecular weights (M e ) are predicted, depending on the method used; the plateau modulus estimates M e of about 8 ϫ 10 5 g/mol, whereas the ratio of mean square end-to-end distance and molecular weight (͗R 2 ͘ 0 /M) predicts M e 's either too small (0.33 g/mol) or too large (2.5 ϫ 10 6 g/mol), depending on the theory used. Although the change in the molecular weight dependency of melt viscosity appears to be associated with the onset of entanglement coupling of the semirigid molecules, its origin needs further investigation.

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“…a=3ck8 T<uu)+Pl (3) here c is the number of rods per unit volume, k 8 the Boltzmann constant, T the absolute temperature, P the hydrostatic pressure, uu indicates the diadic product of u and u, and 1 the unit tensor. The average is taken over the orientational-distribution function determined from eq I.…”

mentioning

confidence: 99%

Nonlinear Viscoelasticity of Concentrated Solution of Rod-like Polymers

Kuzuu

Doi

1980

Polym J

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ABSTRACT:The nonlinear viscoelasticity of concentrated solutions of rod-like polymers in the isotropic phase was studied theoretically based on the molecular diffusion equation of DoiEdwards. Rheological functions were calculated for both shear and elongational flows in a steady, and transient state. The viscoelastic properties of this system were found to be very similar to those of flexible polymers despite the difference in molecular shape and the mechanism of Brownian motion: e.g., shear thinning, normal stresses, and stress overshoot were predicted for rod-like polymers.KEY WORDSThe viscoelastic properties of concentrated solution of rod-like polymers are very important from the stand point of industrial application. 1 In the past ten years, several experimental and theoretical studies have been reported. 2 -6 Though the transient flow and elongational flow are important in fiber or film formation processes, the studies so far carried out are mostly concerned with the linear viscoelasticity, or the steady-state simple shear flow. In this paper, we study theoretically the nonlinear viscoelasticity of this system under simple shear and elongational flows in both the steady state, and the transient state. We show that the viscoelastic properties of this system are qualitatively very similar to those of flexible polymers.The Brownian motion of rigid rod-like polymers in a concentrated solution in the isotropic phase has been discussed by Doi 7 and Doi-Edwards, 8 • 9 and the formula for calculating the stress tensor for a given velocity gradient is presented in ref 9.According to 9 given the history of the velocity gradient, the stress at time t can be calculated as follows.Let u be the unit vector parallel to a rod and f(u; t) be its orientatiorial-distribution function at

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Comparison of the Rheological Properties of Concentrated Solutions of a Rodlike and a Flexible Chain Polyamide

Cited by 57 publications

References 6 publications

Comparison of the Conformation of Tomato Pectins With Apple and Citrus Pectins

Comparison of the Conformation of Tomato Pectins With Apple and Citrus Pectins

Molecular dimensions and melt rheology of an all‐aromatic liquid crystalline polymer

Nonlinear Viscoelasticity of Concentrated Solution of Rod-like Polymers

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