The Effect of Temperature and Solvent Type on the Intrinsic Viscosity of High-Polymer Solutions

1942 ◽  
Vol 15 (4) ◽  
pp. 820-825
Author(s):  
T. Alfrey ◽  
A. Bartovics ◽  
H. Mark
Keyword(s):  
Molecular Shape ◽  
Effect Of Temperature ◽  
Quadratic Term ◽  
High Polymer ◽  
Dilute Solution ◽  
Specific Viscosity ◽  
Solvent Type ◽  
Polystyrene Solution ◽  
Pure Methanol ◽  
Poor Solvent

Abstract 1. The specific viscosity of a dilute solution of polystyrene or rubber is strongly dependent on the nature of the solvent; the specific viscosity is high in a good solvent, and low in a poor solvent or a solvent-nonsolvent mixture. This has been interpreted as being due to changes in mean molecular shape. The specific viscosities of cellulose acetate solutions are not so sensitive to the nature of the solvent. 2. The extrapolated specific viscosity at the limit of solubility is in the same range for several different solvent-nonsolvent systems. 3. The effect of a temperature increase is to lower the specific viscosity of rubber or polystyrene solutions in a good solvent, but to increase the specific viscosity in a mixture of solvent and nonsolvent. 4. The specific viscosity of a dilute polystyrene solution is more nearly linear with concentration in a toluene-methanol mixture than in pure methanol. The quadratic term b in the equation: (ηsp=ac+bc2), is reduced relatively more than the linear term a by the presence of the nonsolvent.

The direct observation of polymer molecules and determination of their molecular weight

1964 ◽  
Vol 279 (1376) ◽  
pp. 50-61 ◽  
Keyword(s):  
Molecular Weight ◽  
Direct Observation ◽  
Particle Diameter ◽  
Dilute Solution ◽  
Crystalline Polymers ◽  
Polymer Molecules ◽  
Molecular Weights ◽  
Preferential Evaporation ◽  
Poor Solvent

An experimental investigation of the conditions necessary for the production of compact, single polymer molecules, in a form suitable for direct observation in the electron microscope, is described. Molecules are isolated by dispersing a dilute solution of the polymer as fine droplets on to a suitable substrate: ideally each droplet should contain either one or no polymer molecules. The solution is a mixture of two solvents, a good one and a poor one. Initially the good solvent predominates so that the probability of polymer aggregation is low. Preferential evaporation of the relatively volatile solvent on the substrate itself gives the poor solvent conditions needed for the formation of well-defined molecular spheres. Factors determining the choice of solvent, precipitant, and the composition of the mixture are discussed. There is little difficulty in obtaining single molecules with glassy amorphus polymers; rubbery polymers collapse and spherical molecules are formed only if the entire preparation is carried out at a temperature below that of the glass transition; crystalline polymers are not amenable to this technique. To obtain sufficient contrast the particles have to be shadowed and it is shown that, although certain dimensions are distorted by the metal coating, the shadow length faithfully represents the true particle diameter. Molecular weights, and their distribution, when of the order of a million and above, can readily be accurately determined. Conventional methods are unreliable in this region of high molecular weight.

Chromatographic Fractionation of Some Synthetic Elastomers

1948 ◽  
Vol 21 (3) ◽  
pp. 682-683 ◽  
Author(s):  
Ivan Landler
Keyword(s):  
Molecular Weight ◽  
Cellulose Acetate ◽  
Active Carbon ◽  
Low Molecular Weight ◽  
High Polymer ◽  
Acrylonitrile Copolymer ◽  
Molecular Weights ◽  
The Mean ◽  
Mean Molecular Weight ◽  
Poor Solvent

Abstract Mark and Saito were the first to fractionate a high polymer (cellulose acetate) by chromatographic adsorption on blood carbon. They found that molecules of low molecular weight were adsorbed first, and that the mean molecular weight of the product which remained unadsorbed was higher than the original molecular weight. Levi and Giera confirmed this result, but did not succeed in fractionating Buna-S or polyisoprene, for these polymers were eluted by the solvent during the washing operation in the column. The present authors have carried out further experiments in this field with a study of three commercial synthetic elastomers, viz., GR-S (butadienestyrene copolymer), Perbunan-N (butadiene-acrylonitrile copolymer), and Visitanex (polyisobutylene). The polymer was adsorbed by starting with a poor solvent composed of a mixture of toluene and methanol ; the quantity of alcohol added was just below the threshold of precipitation. The adsorbent used was a mixture of 75 per cent of lamp black (80 square meters per gram) and 25 per cent of coarse active carbon. The latter served to prevent agglomeration of the lamp black. The adsorbent was divided into three layers, of 10 grams each. At the end of the tube was a filter of fritted glass. Filtration was carried out under pressure, the rate of flow thereby being maintained constant, The polymers were characterized by their intrinsic viscosities. The molecular weights which were estimated by means of the relation, found experimentally between the molecular weight and viscosity, are only approximate, for this relation holds true only for narrow fractions.

Direct Observations of Polymer Molecules and Determination of their Molecular Weight

1966 ◽  
Vol 39 (3) ◽  
pp. 567-580
Author(s):  
M. J. Richardson
Keyword(s):  
Molecular Weight ◽  
Particle Diameter ◽  
Dilute Solution ◽  
Crystalline Polymers ◽  
Polymer Molecules ◽  
Molecular Weights ◽  
Direct Observations ◽  
Preferential Evaporation ◽  
Poor Solvent

Abstract An experimental investigation of the conditions necessary for the production of compact, single polymer molecules, in a form suitable for direct observation in the electron microscope, is described. Molecules are isolated by dispersing a dilute solution of the polymer as fine droplets on to a suitable substrate: ideally each droplet should contain either one or no polymer molecules. The solution is a mixture of two solvents, a good one and a poor one. Initially the good solvent predominates so that the probability of polymer aggregation is low. Preferential evaporation of the relatively volatile solvent on the substrate itself gives the poor solvent conditions needed for the formation of well-defined molecular spheres. Factors determining the choice of solvent, precipitant, and the composition of the mixture are discussed. There is little difficulty in obtaining single molecules with glassy amorphous polymers; rubbery polymers collapse and spherical molecules are formed only if the entire preparation is carried out at a temperature below that of the glass transition; crystalline polymers are not amenable to this technique. To obtain sufficient contrast the particles have to be shadowed and it is shown that, although certain dimensions are distorted by the metal coating, the shadow length faithfully represents the true particle diameter. Molecular weights, and their distribution, when of the order of a million and above, can readily be accurately determined. Conventional methods are unreliable in this region of high molecular weight.

scholarly journals Effects of temperature on actin polymerized by Ca2+. Direct evidence of fragmentation

1985 ◽  
Vol 232 (1) ◽  
pp. 297-300 ◽  
Author(s):  
E Grazi ◽  
G Trombetta
Keyword(s):  
Electron Microscopy ◽  
Direct Evidence ◽  
Monomer Conversion ◽  
Effect Of Temperature ◽  
Specific Viscosity ◽  
Effects Of Temperature

When the temperature is lowered from 20 to 4 degrees C, the specific viscosity of actin polymerized in the presence of either 4 mM-CaCl2 or 2 mM-MgCl2, but not of actin polymerized in the presence of 90 mM-KCl, is decreased by 50% in the absence of free ATP. Addition of ATP restores the viscosity of the actin polymerized by Mg2+, but not that of actin polymerized by Ca2+, to the original value. The effect of temperature on actin polymerized in the presence of Ca2+ is due to (a) polymer-into-monomer conversion, (b) latero-lateral aggregation of filaments, and (c) fragmentation of the filaments. Fragmentation, as demonstrated by fractional centrifugation and electron microscopy, was the most important of these.

The dielectric constant of a liquid

1953 ◽  
Vol 6 (2) ◽  
pp. 93 ◽  
Author(s):  
AD Buckingham
Keyword(s):  
Dielectric Constant ◽  
Dipole Moment ◽  
Polar Solvent ◽  
Molecular Model ◽  
Principal Direction ◽  
Molecular Shape ◽  
Pure Liquid ◽  
Dilute Solution ◽  
Onsager Theory ◽  
Special Case

Some earlier theories in which attempts have been made to allow for the influence of molecular shape on the static dielectric constant of a liquid are shown to be inaccurate. A general equation is derived for the dielectric constant of a liquid, and this is then applied to a molecular model consisting, in the first instance, of an ellipsoid uniformly polarized in a principal direction, and secondly, to an optically anisotropic ellipsoid ; in both cases the surroundings are assumed to form a continuum. The results of this more general approach applied to several substances are more satisfactory than those obtained by the original Onsager theory. The theory is also applied to mixtures, and in the special case of a dilute solution in a non-polar solvent, the equation of Ross and Sack is obtained when the ellipsoid is isotropic. A correlation has been noted in the discrepancies found when the dipole moment of a substance is calculated by means of observations on the pure liquid and on dilute solutions in a non-polar solvent, using the equations derived in the present paper.

Changes of Dynamic Viscoelastic Properties of Tamarind Gum Aqueous Solutions

2011 ◽  
Vol 239-242 ◽  
pp. 477-480 ◽  
Author(s):  
Wancheng Sittikijyothin
Keyword(s):  
Aqueous Solutions ◽  
Viscoelastic Properties ◽  
Sample Solution ◽  
Effect Of Temperature ◽  
Dilute Solution ◽  
Tamarindus Indica ◽  
Typical Shape ◽  
Concentrated Solution ◽  
Mechanical Spectra

Tamarind gum was obtained from the seeds of Tamarindus indica. It was rich in polysaccharide (79.96%) and protein (13.46%) contents. In this work, the dynamic viscoelastic properties of tamarind gum aqueous solutions were investigated with a Haake Rheometer RS75 as a function of gum concentration and temperature. Four types of sample solution systems: a dilute solution, a concentrated solution, a weak gelled system, and a gelled like system were observed. The effect of concentration showed that the typical shape of the mechanical spectra for the dilute solution occurred for 2.30 wt% and the gelled like behaviour arose for the higher concentration (≥7.05 wt%) as measured at 25°C. While the effect of temperature on the dynamic viscoelastic properties of tamarind gum solution (6.91wt%) showed that the gum solution behaved the weak gelled system (25°C) and subsequently gelled like system (≥30°C).

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