The viscosity dependence on concentration,molecular weight and shear rate of xanthan solutions

Summary This paper concerns the viscosity dependence of Xanthan as a function of polymer concentration, shear rate and molecular weight in the ordered conformation. The different samples with various molecular weights are obtained by ultrasonication. A unique curve is obtained for the reduced specific viscosity ( ) as a function of γ · γ _r ⁻¹ for the different molecular weight samples and polymer concentrations below an overlap concentration C [η]₀⩽ 1.5. The master curve giving the relation as a function of C [η]₀ is drawn and compared with that of polystyrene in good solvent. The largest increase of in semidilute solution may be due to larger interchain interactions and to larger stiffness of the Xanthan molecule.     

Concentration dependence of the diffusion coefficient in polymer solution and molecular weight distribution determined by the diffusion method

The effects of the concentration dependence of the diffusion coefficient of a polymer solution (polystyrene in benzene and cyclohexane) in determining molecular weight distribution by the diffusion method are briefly discussed. The value of the ratio D_m0/D_A0 in a good solvent was found to be close to 1.0 for a polydisperse polymer and less than 1.0 for monodisperse polymers. Molecular weight distribution curves of the polydisperse sample were obtained by the diffusion method in cyclohexane and benzene, respectively. The molecular weight distribution curve obtained for the polymer used in benzene solution looked as if the polymer had a narrow molecular weight distribution. The phenomena cited above were interpreted in the light of the concentration dependence of the diffusion coefficient of polymer solutions.     

Examination of the temperature coefficient of polystyrene. Effect of solvent,temperature, and molecular weight

The temperature coefficient of polystyrene was examined in three θ solvents by several different methods. Four homogeneous samples were employed, having molecular weights of 51,000, 97,200, 160,000, and 392,000. It was found that the linear expansion factor α and the temperature coefficient were dependent upon the solvent, temperature range and molecular weight of the polymer.     

Influence of temperature,molecular weight,and molecular weight dispersity on the surface tension of polystyrene,polypropylene, and polyethylene. II. Theoretical

Experimental data for the surface tension of polystyrenes of different molecular weights (3400–200,000) and different molecular weight dispersities (1–3) and of different polyolefins are compared with the predictions of the Patterson–Rastogi and Dee–Sauer cell theories, which infer the surface tension from pressure–volume–temperature (PVT) data. PVT data for these polymers were obtained from the literature and experimentally and are fitted to the Flory–Orwoll–Vrij equation of state. Both theories predict that the surface tension will decrease linearly with increasing temperature and increase with molecular weight, thereby corroborating the experimental data. However, both theories underestimate the entropy change in the surface formation per unit area at a constant volume for low molecular weight and polydisperse systems and underestimate the effect of molecular weight dispersity on surface tension. Both theories feature two parameters, m and b, that quantify the enthalpic and entropic contributions to surface tension. The theoretical predictions are fitted to the experimental data for monodisperse polystyrene (with a molecular weight above the molecular weight of entanglement), polypropylene, and linear low‐density polyethylene to quantify the enthalpic contribution to surface tension. b is then evaluated as a function of molecular weight and molecular weight dispersity and is found to decrease with increasing molecular weight and to increase with increasing molecular weight dispersity, showing that end‐group excess at the surface has some effect on surface tension. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2201–2212, 2002     

Influence of temperature,molecular weight,and polydispersity of polystyrene on interfacial tension between low‐density polyethylene and polystyrene

In this work, the influence of temperature, molecular weight, and polydispersity of polystyrene on interfacial tension between low‐density polyethylene (LDPE) and polystyrene (PS) was evaluated using the pendant drop method. It was shown that interfacial tension between LDPE and PS decreases with increasing temperature for all LDPE–PS pairs studied. The temperature coefficient (∂γ/∂T) (where λ is interfacial tension and T is temperature) was higher for lower molecular weight and larger polydispersity of PS. The interfacial tension between LDPE and PS at a temperature of 202°C increased when the molecular weight of polystyrene was varied from 13,000 to 30,000. When the molecular weight of PS was further increased, the interfacial tension was shown to level off. The effect of polydispersity on interfacial tension between PS and LDPE, at a temperature of 202°C, was studied using PS with a constant‐number average molecular weight and varying polydispersity. The interfacial tension was shown to decrease with increasing polydispersity. However, the influence of polydispersity was lower for PS of higher molecular weight. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2423–2431, 1999     

Temperature and concentration dependence of diffusion coefficient in dilute solutions

Temperature and molecular weight dependence of k_D in D(C) = D(O) [1 + Ck_D], where D(C) is the diffusion coefficient for the density fluctuations in a dilute polymer solution, is investigated by first expressing D(C) as a function of the static structure factor S(q,C) within the framework of the Kirkwood-Riseman theory. The continuous transition of k_D from negative values under theta conditions to positive values in good solvents is calculated using various models for the intermolecular interaction potential and the results are presented graphically as function of a reduced variables $\text{S}\text{?}\text{R}{}_{\mathrm{H}}$ that combines both molecular weight and temperature effects. It is shown that the negative value of k_D at the theta temperature can be explained at least partially, in terms of an increase in the chain dimensions of two overlapping molecules. The concentration dependence of the self-diffusion coefficient is also discussed.     

A study on the concentration dependence of excimer formation in pyrenyl labelled polystyrene solutions

The fluorescence of pyrenyl labelled polystyrene has been investigated. The ratio of excimer to monomer intensities (I_e/I_m) is found to vary tortuously with increasing concentration (C) and displays two critical concentration points, C⁺ at about 3.2 × 10⁻² g ml⁻¹ and C_m at about 0.32 g ml⁻¹. In the region C⁺ < C < C_m, an abrupt increase of I_e/I_m is revealed because of intermolecular interaction. At C > C_m, the sharp decrease of I_e/I_m is ascribed to entanglements of polymer chains. © 1999 Society of Chemical Industry     

Sorption equilibria and diffusion of toluene,methanol, and cyclohexane in/through elastomers

Molecular transport of toluene, methanol, and cyclohexane and their mixtures in Chemraz 505 elastomer has been investigated using gravimetric techniques for short and long time exposure in these solvents. The sorption–desorption results have been used to calculate the diffusion coefficients by solving Fick's equation under appropriate boundary conditions. The dependence of sorption, desorption, diffusion, and permeation on temperature and composition changes was also studied. The results are discussed in terms of possible interactions between Chemraz 505 polymer and the solvent molecules. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43449.     

Effect of solvent,concentration, and molecular weight on the rheological properties of polymer solutions

The zero-shear viscosity η⁰ of polychloroprene samples of different molecular weights over a wide range of concentration in good and poor solvents has been studied. Butanone and cyclohexane were used as θ solvents and benzene at two different temperatures (25 and 45.5°C) was used as two good solvents. The zero shear specific viscosity η in θ solvents, at the high concentration region is found to be higher compared to the values obtained in good solvents. whereas in a moderately concentrated region the values are just opposite in θ and good solvents. The high values of specific viscosity in poor solvent at the concentrated region have been explained as due to the fact that the efficiency of entanglements is much bigger in θ solvent than in good solvent. There are indications from our data that, at the crossover point concentration, the onset of entanglements begins, and from this concentration the entanglement begins to play a role in the viscosity. The superposition of viscosity data for each solvent was carried out by shifting vertically the curve along log η⁰ axis at constant concentration by a factor (M/M⁰)^3.4, where M⁰ is the molecular weight of the reference sample. The shift factor was found to be exactly proportional to M^3.4 in the range of higher concentration (beyond the crossover point concentration) and approximately to M in the lower concentration range (below the crossover point concentration). This showed that the relation η⁰ ∝ M^3.4 was obeyed by the present data. To correlate the viscosity data obtained at good and θ solvents, the method as given by Graessley has been employed, which has taken into account the contraction of dimensions of chains with concentration in good solvents. It has been observed that, though this approximate correction for variation of chain dimensions on correlating variable, C[η], has moved the correlations for θ and good solvents closer to a common curve, complete superposition of data has not been effected by this correction. On the other hand, the correlation of the data by the method given by Dreval and co-workers showed the plot of log{η/(C[η])} vs. C[η] produced a single curve for solutions of polychloroprene samples in two different θ solvents (butanone and cyclohexane) over the entire concentration range. But in the case of good solvents (benzene at 25°C and benzene at 45.5°C) the similar plots yielded, instead of one, two curves. However, the normalization of the correlating variable, C[η], by the Martin constant K_M, which is related to the flexibility of macromolecular chain and polymer-solvent interaction, reduced all data of the polymer samples to a common curve. This zero-shear viscosity master curve is valid for the entire range of concentration independent of molecular weight and the nature of solvents.     

A method for determination of thermodynamic and solubility parameters of polymers from temperature and molecular weight dependence of intrinsic viscosity

An equation using the temperature dependence of intrinsic viscosity of a polymer was proposed for the determination of the partial molar entropy and enthalpy changes of the polymer for mixing in dilute solution. It was found that the partial molar entropy change of a polymer for mixing at a given temperature is proportional to the hydrodynamic volume or segment number of the polymer. The partial molar enthalpy change of the polymer for mixing was determined from the thermodynamic equilibrium property of polymer phases. The solubility or cohesion parameter of a polymer fraction was calculated by using the partial molar enthalpy change and repeat unit volume of the polymer. The solubility parameter of high molar mass polymer at a given temperature was determined by extrapolating solubility parameter values of polymer fractions to high molar mass by using the solubility parameter-segment number relation of polymer fraction. This relation gives a straight line. The solubility parameter of the polymer at a given temperature and the effective interchange energy parameter for polymer-solvent pair were obtained directly from the intercept and the slope of this line, respectively. These equations were applied to the intrinsic viscosity-temperature data of polystyrene fractions in decalin solutions, and polystyrene fractions in decalin, cyclohexane and dioctyl phthalate solutions at the theta temperatures and in toluene solutions at the given temperatures. The results obtained in this study coincide with the literature values. In addition, it was given a relation, which is derived from the blob theory for the temperatures above the theta point, for the estimation of the thermodynamic parameters of polymers for mixing.     

Volumetric properties of polystyrene: influence of temperature,molecular weight and thermal treatment

Specific volumes (v) of a series of anionic polystyrenes (M = 2000 to 2 000 000) have been measured dilatometrically over the temperature range ?30° to 210°C. General equations are given for v as a function of temperature and molecular weight and are used to calculate glass temperatures and free volumes.     

Polymer chain dimensions and the dependence of viscoelastic properties on concentration,molecular weight and solvent power

The effects of polymer concentration on chain dimensions in good solvents is discussed in order to define the boundary between the semi-dilute and concentrated regimes. Based upon the screening principle of Edwards and de Gennes, it appears that chain dimensions should approach their unperturbed values for many systems at polymer volume fractions in the range of 0.05–0.20, independent of molecular weight. From these results we propose a method for correlating viscoelastic properties in the semi-dilute region which takes into account the contraction of dimensions with concentration. We also suggest the use of a concentration-molecular weight diagram to distinguish the several regions of viscoelastic behaviour.     

Thermodynamic parameters of viscous flow for electrolytic solutions in N,N dimethylformamide—water mixtures

Transition-state treatment has been used for calculation of the contributions per mole of the solute to the free energy of activation for viscous flow of lithium chloride, lithium nitrate and lithium, sodium and potasium perchlorates solutions in dimethylformamide—water mixtures. The values obtained increase with increasing dimethylformamide content in the solvent, except in the case of perchlorates, where a minimum in a water-rich region is observed. This behaviour is interpreted in view of the changes in solvation and molar volumes at infinite dilution of the ions in the different solvent mixtures. Finally, from the free energy-values at different temperatures, the estimated enthalpy and entropy of activation of viscous flow are analysed.     

Influence of concentration and molecular weight on the photosensitized degradation of alginate in aqueous solutions

Summary Riboflavin (RF), photosensitizer, was used in combination with irradiation with light of wavelengths in the range of 310-800 nm to induce degradation of the biopolymer alginate. The effects of molecular weight and concentration were studied. The viscosity increases as the concentration is raised both for the alginate and alginate-RF solutions but is lower for the solutions irradiated in the presence of RF. Similar to many entangled andor associated polymer networks this system shows strong shearthinning effect at higher concentrations. The viscosity change induced by illumination in the presence of RF seems to be most extensive for the solution with the highest molecular weight. This was emphasized by oscillatory shear measurements, which indicate that RF in combination with irradiation has most effect on the rheological parameters of alginate of the highest molecular weight.     

Light-scattering studies on solutions of high and low molecular weight polystyrene mixtures used as models of microgel-containing solutions

Diluted solutions of linear polystyrene (PS) in toluene and dioxane were studied by the light-scattering method. The solutes were mixtures of high-M?_w and low M?_w PS. The dissolved PS mixtures were regarded as polymer solutions containing microgels, the high-M?_w PS being looked upon as the microgel counterpart. The calculation method as proposed by Strazielle¹ and Burchard² was used to evaluate the microgel percentage and particle size, whereby the method could be verified against mixtures with well-known weight composition and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document}. The \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values evaluated for the mixtures from the experimental data were compared with those estimated from the molecular weights of the components, their weight concentrations, and their \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values. The method^1,2 was found to be useful for evaluating the microgel content in a sample, but not for \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} values as calculated by Guinier's procedure nor those calculated by Zimm's procedure; the former were low and the latter were even incongruous. A comparative analysis of the theoretical function P^?1(θ)-versus-sin² (θ/2) and experimental (Kc/R(θ))_c=0-versus-sin² (θ/2) curves allowed to discuss the effect of the course of these curves at samll angles from 0° to 30° on M?_w and \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {\left( {r_g ^2 } \right)} ^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} $\end{document} as determined for the high and low molecular weight polystyrene mixtures in toluene as solvent.     

Influence of molecular weight on strain‐gradient yielding in polystyrene

Experimental observations have indicated that the presence of strain gradients has an influence on the inelastic behavior of polymers as well as in other materials such as ceramics and metals. The present study has experimentally quantified length‐scale effects in inelastic deformations of the polymer material polystyrene (PS) with respect to the molecular length. The experimental technique that has been used is nano‐indentation to various depths with a Berkovich indenter. The hardness has been calculated with the method by Oliver and Pharr, and also by direct measurements of the area from atomic force microscopy. The experiments showed that the length‐scale effects in inelastic deformations exist in polystyrene at ambient conditions. The direct method gave a smaller hardness than the Oliver‐Pharr method. It was also shown that the length‐scale parameter according to Nix and Gao increases with increasing molecular weight. For high molecular weights above a critical value of entanglement, there was no pertinent increase in the length‐scale parameter. The length‐scale parameter for strain‐gradient plasticity has a size of around 0.1 μm for polystyrene. Polym. Eng. Sci. 44:1987–1997, 2004. © 2004 Society of Plastics Engineers.     

Co-operative diffusion of semi-dilute solutions, concentrated solutions and swollen networks for polystyrene in dibutylphthalate

The diffusion constant of solutions of polystyrenes of molecular weight ranging from 110 000 to 3.6 × 10⁶ in straight-chain-dibutylphthalate has been measured by photon correlation spectroscopy as a function of polymer volume fraction and temperature. In the semi-dilute range the co-operative diffusion constant D_c exhibits a much smaller increase with the polymer volume fraction Φ than theoretically predicted, except at high temperatures (T 100°C) where it follows a Φ^1/2 law characteristic of a marginal solvent. This effect can be described to an enhancement of the friction factor, which is also demonstrated by a decrease in D_c occurring at a volume fraction which increases with temperature. The same effect is observed in swollen networks but it is strongly reduced for swelling equilibrium conditions.