Rheological behavior of concentrated polystyrene solutions in good and in poor solvents

Tager, A.A.; Dreval, V. E.; Lutsky, M. S.; Vinogradov, G. V.

doi:10.1002/polc.5070230123

Cited by 15 publications

(11 citation statements)

References 15 publications

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“…From qo(c;T) measurements, Debye et al 1221 found that plots of d !2n VJdT vs. c exhibited pronounced maxima in the moderate concentration range as T approached the theta temperature. Anomalous qo(c; S ) data, similar to those reported here, were observed as early as 1945 by Janssen and Caldwell [23] and more recently by Tager et al [24]. The latter workers also demonstrated the marked differences in non-Newtonian character observed for good-solvent and poor-solvent systems.…”

Section: Discussionsupporting

confidence: 88%

Solvent effects on the viscosity of moderately concentrated polymer solutions

Gandhi

Williams

1971

J. polym. sci., C Polym. symp.

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Viscosity ηo and osmotic pressure π were measured for polymer solutions at 25°C, for concentrations up to 30 g/dl. To elucidate the effects of polymer‐solvent interactions of various types, the systems chosen were polystyrene in toluene (good solvent) and decalin (poor solvent), and poly(methylmethacrylate) in chlorobenzene (good) and m‐xylene (poor). The surprising result was the generalization that ηo for poor‐solvent systems increases with concentration faster than for good‐solvent systems, so that eventually ηo becomes far greater with poor solvents. This behavior is enhanced with polar polymers, and is not explainable on the basis of entanglements in the usual sense. It is believed that polymer aggregation occurs in poor solvents, independent of molecular weight effects. Data were correlated with both the powerlaw and the Simha methods. Characteristic shapes of such curves were related to polymer‐solvent effects. Theories for the Huggins constant were found to be inadequate, as was a model proposed earlier (by MCW) for concentrated solutions. The latter was modified by adopting an ad hoc friction constant, which proved successful with good solvents and could be correlated with π to incorporate the poor‐solvent data as well.

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Section: Discussionsupporting

confidence: 88%

Solvent effects on the viscosity of moderately concentrated polymer solutions

Gandhi

Williams

1971

J. polym. sci., C Polym. symp.

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“…On the other hand, this linear dependence of E η on concentration differs from the corresponding relationships that are typically found for the solutions of linear and/or randomly branched chain polymers, where a break in E η vs c slope is normally observed . Since the appearance of this break may be associated with establishment of entanglement couplings, the observed linearity of E η vs c in dendrimer solutions seems to represent yet another manifestation of dendrimer impenetrability to other dendrimers or their parts.…”

Section: Resultsmentioning

confidence: 98%

Rheology of Dendrimers. I. Newtonian Flow Behavior of Medium and Highly Concentrated Solutions of Polyamidoamine (PAMAM) Dendrimers in Ethylenediamine (EDA) Solvent

et al. 1998

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Steady shear flow properties of an extensive family of dendrimers were examined for the first time in medium to high concentration solutions. For this, the first seven generations of ethylenediamine (EDA) core-polyamidoamine (PAMAM) dendrimers, having molecular weights from about 500 to almost 60 000 in 30 to 75 wt % solutions in ethylenediamine (EDA) were used. It was found that these dendrimer solutions exhibited typical Newtonian flow behavior as manifested by direct proportionality of the shear stress to the shear rate (i.e., constant viscosity with respect to both shear stress and shear rate) over the entire range of shear stress and shear rate studied. In addition to this, there was no abrupt change in the slope of the shear viscosity vs molecular weight relationship, indicating that these dendrimers do not interpenetrate to form transient quasi-networks of the "entanglement"-type typically found for long-chain linear or randomly branched macromolecules, nor do they engage in "sticking" interactions characteristic for the suspensions of idealized spherical particles. This rheological behavior is without precedence among high molecular weight synthetic polymers, and it is proposed that it is solely driven by the unique dendrimer macromolecular architecture which above a certain critical generation results in globular, nanoscopic spheroids whose outer surfaces close upon themselves and become impenetrable for other dendrimers or large molecules. The shear viscosity vs volume fraction dependencies showed that these dendrimers are draining to solvent molecules, but to a lesser extent than the corresponding random-coil type linear macromolecules of comparable molecular weights. These findings are consistent with a "dense-shell" model of dendrimer intramolecular morphology which can also explain their ability to encapsulate small molecular weight species in their "soft and spongy" interiors. From a typical Arrhenius-type temperature dependence of these dendrimer solutions viscosities and from the dependencies of their flow activation energy on molecular weight, it seems that the smallest kinetic unit involved in the dendrimer flow is the dendrimer molecule itself. Strong dependence of the dendrimer solution viscosity on concentration and temperature, as well as its independence on repeated loading, indicates substantial dendrimer flexibility and ability to deform. On the basis of these results and the supporting computer modeling calculations, it is proposed that the Newtonian flow behavior and the lack of an abrupt change of slope in the zero-shear viscosity vs molecular weight relationships represent characteristic "fingerprint" properties for dendrimers in general and that these properties distinguish these unique macromolecules from all other traditional classes of macromolecular architecture. It is also proposed that the critical degree of branching may be used as a defining structural criterion for distinguishing true dendrimers from their low molecular weight simple branched precursors.

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“…This model was first proposed by Kargin et al") for the conformation of bulk polymers, and applied to concentrated solutions by Tuger et a1. 20).…”

Section: Introductionmentioning

confidence: 99%

Small‐angle X‐ray scattering study on concentration dependence of polymer chain dimension

1977

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The concentration dependence of polymer chain dimensions was studied by a new type of "tagged polymer method in small-angle X-ray scattering. A small fraction of partially iodinated polystyrene, the tagged polymer, was mixed with polystyrene in toluene. From the excess scattering originated from the iodine, the radius of gyration of the polystyrene chain (M,= 110000) was estimated at various concentrations. It was found that the chain dimension decreases first rapidly and then decreases gradually with increasing polymer concentration, and that, in the bulk, it coincides with the unperturbed chain dimension. The result was compared with theoretical predictions. The theories applicable to low concentrations could predict well the chain dimension uptomassconcentrations ofca. 0,l g/cm3, while the theoriesapplicable to higher concentrations could not predict well the chain dimension at high concentrations. The conformation of the polymer chain was also discussed. More compact conformations than a random coil as well as the bundle model were not supported by the results. *I Vollmrrt et al. proposed this model from studies on polymer-polymer reaction, whereas,Worsfold'8', using the analogous method, has claimed that the procedure of Vollmert was inadequate, and that the polymer chains are freely interpenetrating. Recently, Vollmert himself' 9 , has modified his model based on further experiments.

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Rheological behavior of concentrated polystyrene solutions in good and in poor solvents

Cited by 15 publications

References 15 publications

Solvent effects on the viscosity of moderately concentrated polymer solutions

Solvent effects on the viscosity of moderately concentrated polymer solutions

Rheology of Dendrimers. I. Newtonian Flow Behavior of Medium and Highly Concentrated Solutions of Polyamidoamine (PAMAM) Dendrimers in Ethylenediamine (EDA) Solvent

Small‐angle X‐ray scattering study on concentration dependence of polymer chain dimension

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