Viscosity observations

Schulze and Crouch [7] observed that the viscosity of the soluble fraction of copolymers from butadiene and styrene decreased sharply with the conversion after an initial increase up to the point of gelation. This decrease could not be solely attributed to a selective incorporation of higher molecular mass fractions in the gel, thus leaving fractions of low molecular mass in solution. Cragg and Manson [8] reported a similar relationship between the intrinsic viscosity and the fraction of the crosslinking DVB in the ECP with styrene. Within the concentration range up to 0.1 mass % of DVB no gel was formed. Therefore, a selective removal of species with a high molecular mass could not have taken place to explain the decrease in the intrinsic viscosity observed after its increase at lower concentrations of DVB. 

The complex viscosity, i.e., the viscosity observed in the presence of an oscillatory shear rate, is a dynamic property that can be straightforwardly obtained from the Rouse, or Rouse-Zimm theory as the Fourier transform of the stress time-correlation function. Thus, these theories give [15]... 

The studies of Pauli he. cit.) and his co-workers, however, have revealed the fact that isohydric solutions of different acids do not effect equal combination with the isoelectric protein relatively more acetic acid for example being combined than hydrochloric acid in isohydric solutions. Again, both the actual position of these maxima as well as the magnitudes of the viscosities observed vary much with the nature of the acid employed. Thus the relatively weak oxalic acid appears to be a much stronger acid than sulphuric acid, whilst trichloracetic acid does not differ appreciably from acetic acid in its effect on the viscosity of albumin. It is probable that the degree of solvation of the protein molecules and of the protein salts must not be regarded as constant but that they vary both with the nature of the salt and in the presence of neutral salts which exert like alcohol a desolvating action more or less complete on the solvated isoelectric protein as well as on the undissociated protein salts. 

The greater melt viscosities observed for some branched polymers, as compared with linear ones of the same MW, are not accounted for by current theories, as indicated in Section 5. The greater values of the steady state compliance mentioned above is also unexpected theory (128) would suggest a difference in the opposite sense. 

It is widely known that oxygen dissolution in a medium is highly dependent on the medium s viscosity. The decrease observed in the dissolved oxygen concentration is probably associated with the increase in the viscosity observed along the process. The two observations, the decrease in oxygen concentration and the increase in viscosity, were simultaneously observed during the production of EPS by Rhizobium sp. EQ1. 

The ratio of molecular weights(Mh/Mi) is approximately 3, and this was confirmed by independent viscosity observations. 

Meijer et al. reported the self-aggregation behavior of a molecule in chloroform (Fig. 11.8) containing two units of 2-ureido-4-pyrimidone linked through a spacer (which self-associates in the DDAA-AADD pattern strongly with a dimerization constant >106 m ) [36], This compound formed viscous solutions in chloroform, and the viscosity observed was dependent on the concentration and temperature. 

When P. radiata bark is extracted by sulfite-carbonate, the solution viscosities are much lower. For example, Woo (30) reported a viscosity of 1,600 mPa-s for a 45% solution of Tannaphen, a commercial tannin extract from P. radiata bark that contains approximately 70% proanthocyanidins. When extracted with sulfite-carbonate, the proanthocyanidins will be partly depolymerized 31), which will cause a fall in viscosity. Whether the very high viscosities observed for aqueous extracts by Yazaki and Hillis 29) are due to the P, radiata proanthocyanidins being of much higher molecular weight than other conifer tannins or due to complexation of the proanthocyanidins with the polysaccharide fraction 32) remains to be shown. 

Polarity effects exist because the interior of a micelle is less polar the aqueous phase, but more polar (because of water penetration or exposure) than hydrocarbon solvents. Therefore, reactions affected by polarity will have different reactivities in micelles compared to aqueous solution or organic solvents. The actual polarity or viscosity observed by a solute will be a time average value of the various locations which each solute experiences. Therefore, the average location of a solute can be quite different for solutes with different hydrophobicities. 

Beyond the percolation limit, the bridging network is more concentrated. Below the critical volume fraction, no continuously bridging networks are formed and the viscosity is low. As shown in Figure 12.7, this bridging network breaks up as the shear rate increases, giving different viscosities at different shear rates. As a result, this gives low and high shear limit viscosities observed at steady state for concentrated poljmier solutions and concentrated particulate suspensions (discussed later). 

The changes in viscosity observed in solutions of muscle actomyosin on addition of ATP are explained by a dissociation of the actomyosin complex into its component parts, actin and myosin. Since thrombosthenin behaves similarly, it must be assumed that it too has dissociated into the corresponding components, which have been termed thrombosthenin A and thrombosthenin M, (A for actin-like, M for myosin-like) (Bettex-Galland et al., 1962, 1963a). 

The greater viscosity observed in associated liquids is reasonable in view of the increased size and reduced mobility of the H bonded complex. 

Hunt et al. have used ab initio methods to study ion pairs in l-butyl-3-methylimidazolium (Bmim) ILs. The anions were Cl, BF4 , and NTf2". The authors established relationships between ion-pair association energy and a derived parameter called the connectivity index . Overall, the results suggest that Bmim-Cl forms a strongly connected and quite highly structured network, which leads to the rather high viscosity observed experimentally. In contrast, Bmim-NTf2 only forms a rather weak network, where the connectivity and the viscosity are much lower [106],... 

These figures have been compared with those obtained for rabbit acto-myosin and myosin (Hamoir, 1955). These last values differ notably from one author to another especially in the case of actomyosin, but they always remain lower than our determinations. The viscosity numbers determined by Kerekjarto (1952) for rabbit actomyosin and myosin at 15° C., which seem to be the most reliable, are, respectively, 0.32 and 0.17 ( 0.01). Both figures are definitely lower than our values carried out at higher temperature. In the case of actomyosin, this difference appears to be due to the structure of the solutions. Recent determinations (Hamoir, 1955) suggest that fish and rabbit actomyosins have approximately the same intrinsic viscosity at = 0. The axial ratio of these particles seems therefore not to differ notably. In view of this relationship, more accurate determinations are necessary in order to determine if the different viscosities observed in the presence of ATP are really due to a different shape of the particles. 

Figure 7. The effect of tomato juice concentration on the viscosity observed at 20°C by using a disc-rotating viscosimeter...

Figure 13.18. Comparison between model and measurements for clays dispersed in polymers. Viscosities observed as a function of shear rate by Krishnamoorti et al [46] for dispersions of silicate platelets (weight fractions of 0.06 and 0.13) in poly(dimethyl siloxane) at T=301K are indicated with symbols. Calculated results, assuming platelets to be monodisperse flexible cylinders with aspect ratio Af=(thickness/diameter)=0.01, are indicated as lines, (a) Relative viscosity=r)(dispersion)/r (polymer). (b) Dispersion viscosity, r)(dispersion).

The viscosity observations were qualitative and were made by directly comparing resistance to flow upon pouring the particular liquid into the molds. The viscosity of each mixture was compared with the viscosity of elemental sulfur at 120 °C, which was considered low. 

In a high-volume-fraction dispersion with electrosteric stabilization of the latex and an increasing dispersed-phase surface area, the high viscosity observed at low shear rates with decreasing latex size relates to electroviscous and hydration effects. Lower surface acid concentrations on some of the smaller latices may also result in partial flocculation of the latex and a higher effective volume fraction in the presence of coalescing aids (22, 26). 

Irrespective of the free surfactant s effect on the maxima in associative thickener viscosity efficiency, the sum of the maxima in the viscosity of the associative thickener and surfactant and of the latex does not equal the viscosity of the combined components in a coating. A synergistic viscosity increase from an interaction between the thickener and the latex is required to account for the total viscosity observed (26). The most popular mechanism for association is the adsorption of the thickener s hydrophobe(s) on the surface of the latex. 

The urea can be added to the finished PF resin or during its manufacture. The distinct decrease of viscosity observed when urea is added to the finished PF resin is caused by the cleavage of hydrogen bonds [162] and by the dilution effect. There is obviously no cocondensation of this postadded urea with the phenolic resin. Urea reacts only with the free formaldehyde of the resin to form methylols which, however, do not react further due to the high pH [163]. Only at high temperatures did Scopelitis and Pizzi [164] suppose some phenol-urea cocondensation occurs, but in their case the phenol used was the much more reactive resorcinol. 

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