Viscosity adsorbed polymer

The polymers exist in saline solution as tightly coiled chains and are readily adsorbed owing to relatively low solubiUty in hard water. Subsequent injection of soft, low salinity water uncoils the adsorbed polymer chains increasing water viscosity and reducing rock permeabiUty. This technology could also be used to reduce the permeabiUty of thief 2ones adjacent to injection wells. However, mechanical isolation of these 2ones may be necessary for cost-effective treatments. 

It is precisely the loosening of a portion of polymer to which the authors of [47] attribute the observed decrease of viscosity when small quantities of filler are added. In their opinion, the filler particles added to the polymer melt tend to form a double shell (the inner one characterized by high density and a looser outer one) around themselves. The viscosity diminishes until so much filler is added that the entire polymer gets involved in the boundary layer. On further increase of filler content, the boundary layers on the new particles will be formed on account of the already loosened regions of the polymeric matrix. Finally, the layers on all particles become dense and the viscosity rises sharply after that the particle with adsorbed polymer will exhibit the usual hydrodynamic drag. 

PVA and TaM -for the 88%-hydrolyzed PVA. The same dependence was found for the adsorbed layer thickness measured by viscosity and photon correlation spectroscopy. Extension of the adsorption isotherms to higher concentrations gave a second rise in surface concentration, which was attributed to multilayer adsorption and incipient phase separation at the interface. The latex particle size had no effect on the adsorption density however, the thickness of the adsorbed layer increased with increasing particle size, which was attributed to changes in the configuration of the adsorbed polymer molecules. The electrolyte stability of the bare and PVA-covered particles showed that the bare particles coagulated in the primary minimum and the PVA-covered particles flocculated in the secondary minimum and the larger particles were less stable than the smaller particles. 

Among the properties measured here, the settling rate is mainly a measure of the size of the floes and in later stages the compressibility of floes and floe networks, and the supernatant clarity is a measure of the size distribution of floes and size dependent capture of the particles and floes by the polymer. The sediment volume and the pulp viscosity on the other hand, are direct measures, not only of floe size and structure but also of adsorbed polymer layers. It is to be noted in this regard that it is this latter aspect which makes it possible to estimate the thickness of adsorbed polymer layers by measuring the viscosity of the medium and the suspension in the presence of polymers (20,21). This combination of effects is another reason one cannot always expect correlation between various flocculation responses. 

Other dimensionless groups that compare the thickness of the adsorbed polymer layer to the radius of the particle or the radius of gyration of the polymer to the particle radius in polymer/colloid mixtures can also be easily defined. We are mostly concerned with the volume fraction and the Peclet number Pe in our discussions in this chapter. However, the other dimensionless groups may appear in the equations for intrinsic viscosity of dispersions when the dominant effects are electroviscous or sterically induced. 

EXAMPLE 13.5 Determination of the Thickness of Adsorbed Polymer Layer from the Intrinsic Viscosity of the Dispersion. An adsorbed layer of thickness 8RS on the surface of spherical particles of radius R increases the volume fraction occupied by the spheres and therefore makes the intrinsic viscosity of the dispersion greater than predicted by the Einstein theory. Derive an expression that allows the thickness of the adsorbed layer to be calculated from experimental values of intrinsic viscosity. 

Thicknesses of adsorbed polymer layers from the intrinsic viscosity of... 

The most convenient of these methods is viscosity measurement of a liquid in which particles coated with a polymer are dispersed, or measurement of the flow rate of a liquid through a capillary coated with a polymer. Measurement of diffusion coefficients by photon correlation spectroscopy as well as measurement of sedimentation velocity have also been used. Hydrodynamically estimated thicknesses are usually considered to represent the correct thicknesses of the adsorbed polymer layers, but it is worth noting that recent theoretical calculations52, have shown that the hydrodynamic thickness is much greater than the average thickness of loops. 

Ohm26,78-79), among others, called attention to the anomalous viscosity behavior of polymer solutions at very low concentration. Plots of j sp/C against C were found to curve either down or up at such concentrations, and the anomaly was attributed to the adsorption of polymer molecules onto the capillary wall. In order to calculate the thickness of the adsorbed polymer layer, Ohrn used the equation... 

A similar, and even more dramatic, viscosity enhancement was observed by Buscall et al. (1993) for dispersions of 157-nm acrylate particles in white spirit (a mixture of high-boiling hydrocarbons). These particles were stabilized by an adsorbed polymer layer, and then they were depletion-flocculated by addition of a nonadsorbing polyisobutylene polymer. Figure 7-9 shows curves of the relative viscosity versus shear stress for several concentrations of polymer at a particle volume fraction of 0 = 0.40. Note that a polymer concentration of 0.1 % by weight is too low to produce flocculation, and the viscosity is only modestly elevated from that of the solvent. For weight percentages of 0.4-1.0%, however, there is a 3-6 decade increase in the zero-shear viscosity ... 

Absolute porosity, definition, 220 Absolute viscosity, definition, 386 Acid number (total acid number, TAN), definition, 403 Adhesion, definition, 26-27 Adsorbed polymer layers, interaction with droplets, 62 Adsorption definition, 386... 

Electron spin resonance spectroscopy (ESR), also known as electron paramagnetic resonance (EPR), is based on the property that an unpaired electron placed in a magnetic field shows a typical resonance energy absorption spectrum sensitive to its environment. Recently, this technique, which was primarily developed for biological studies of membrane properties, has been adapted for the study of adsorbed polymer/surfactant layers. The mobility of the ESR probe (stable free radical incorporated into the polymer or surfactant molecule) depends of orientation of the surfactant or polymer and the viscosity of the local environment around the probe. 

The prime cause of the surface shear viscosity is friction between surfactant molecules the cause of surface shear elasticity is attractive forces between those molecules, leading to a more or less continuous two-dimensional network. For a closely packed layer, the effects may be substantial. For layers of small-molecule surfactants, however, the values of rif are generally immeasurably small, about 10 5 N s m 1 or less. For adsorbed polymers, values between 10 3 and lN-m-s-1 have been reported. 

In these two equations r/ad, is the viscosity of the adsorbed polymer, >i2e the (non-equilibrium) excess interfacial tension and y,2 the (equilibrium) interfacia] tension, so that the quotient yi2j i2 describes the distance of the thermodynamic system from the equilibrium state. It is ea.sy to see that such behaviour is not at all in accordance with the idea of statistically distributed dispersed phases and non-interacting interfaces. 

It is the increase in surface viscosity produced by adsorbed films (insoluble and Gibbs monolayers, adsorbed polymers, etc.) that leads to the production of persistent foams, helps stabilize emulsions, and explains the role of spread monolayers in dampening surface waves, among other important interfacial phenomena. 

The Dynamic Light Scattering (DLS) technique was used to measure radii of the PS latex spheres with and without adsorbed polymer brushes. We could then deduce the polymer brush hydrodynamic layer thickness by taking the difference of the radii. DLS measures the intensity autocorrelation as a function of delay time, which gives information on the diffusion constant of particles in a dilute solution. The translational diffusion coefficient, D, is related to the solution temperature T, particle radius r, and solvent viscosity ri by the Stokes-Einstein relation ... 

Several methods may be used to determine the adsorbed layer thickness, 8. Most of the methods depend on measuring the hydrodynamic radius of the particles with and without the adsorbed polymer layer. For example, one may measure the relative viscosity, of a dispersion with an adsorbed polymer layer. Assuming that the particles behave as hard spheres (when 8 is small compared with the particle radius R) of noninteracting units (low volume fraction of the disperse phase), can be related to the effective volume fraction, [Pg.355]

By carrying out the measurements in the presence and absence of polymer layers, one can obtain 8. In the presence of an adsorbed polymer layer, the hydrodynamic radius is the sum of the core radius and the adsorbed layer thickness, whereas in the absence of the polymer layer, 7 is simply the core radius. Again, as with the viscosity technique, this method cannot be directly applied to emulsions, which are polydisperse and with a radius that is large for significant Brownian motion. 

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