Polymers as Rheology Modifiers

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Old Password. New Password. In this case the resin only viscosity was on the order of 20 Pas. As the shear stress increases, the shearing fields begin to break down the particle agglomerates resulting in a decrease in the viscosity. The shear stress was incrementally increased until point B indicated by the two arrows above the top viscosity curve. Near point B, the viscosity does not appreciably change with incremental increases in the shear stress, possibly indicating the fumed silica has been broken down to the dispersed aggregates and potentially some dispersed particles.

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After the shear stress reached point B, the shear stress ramp was reversed as shown in the direction of the arrow below the lower viscosity curve. From point B to C, the shear stress was incrementally decreased. The shear stress was decreased until approximately 2 Pa. There are a couple of interesting features to note in the decreasing shear stress ramp. As the shear stress decreases, at the high shear stresses, the viscosity during the recovery is pretty similar to the top curve.

As the shear stress decreases, the deviation of the lower curve becomes more pronounced. Additionally, one notes that the yield stress the approximate stress at point C is about 2 Pa whereas the initial yield stress was approximately 10 Pa.

Your email address will not be published. Save my name, email, and website in this browser for the next time I comment. Schematic of the morphology of fumed silica at different process stages reference [1] The particles from the flame hydrolysis form aggregates in the size range of nm. Schematic of particle-particle interactions in fumed silica reference [1] As seen on the top in Figure 2, strong particle-particle attraction, in this case hydrogen bonding between the surface hydroxyl groups leads to aggregates. The next post will discuss in more detail the concepts of thixotropy and shear thinning.

Because of their technical application, the absorption capacity of gel blocks and their reversibility of swelling in salt solutions with multivalent cations have been studied. A method based on very few experimental data was introduced, which allows to determine the parameters necessary for predicting the degree of swelling at any desired salt concentration. In addition, rheological investigations on gel blocks and particle solutions provide information about regions where inhomogeneities occur and data for determining the absorption capacities and their elasticity values.

Electrophoretic mobility measurements show that the PEO is truly grafted, not just adsorbed. Steady shear and oscillatory rheological measurements indicate a transition from primarily liquid-like behavior to solid-like behavior at an effective volume fraction between 0.

Rheology: The Study of Flow

The rheological behavior is interpreted in terms of long-range repulsive particle interactions due to the grafted polymer layers. These measurements thus provide a useful probe of the relationship between polymeric interactions, suspension microstructure, and macroscopic material properties. Hydrophobic modification of poly acrylic acid thickeners yields products that are useful as primary emulsifiers for oil-in-water systems. The resulting emulsions are stable for years, but they break and coalesce almost instantly when a sufficient concentration of electrolyte is introduced into the aqueous phase.

The effect of electrolytes on these electrosterically stabilized emulsions is complex.

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The polymer is anchored to the oil droplet by hydrophobic interaction. Such anchoring should theoretically be strengthened by the presence of water-structure-enhancing electrolytes. On the other hand, coulombic interaction between the electrolyte and the polyelectrolyte causes shrinkage of the overall polyelectrolyte configuration and this should theoretically make coalescence more likely. Emulsion polymerization process conditions and chemical modifiers often affect the physical characteristics of the latex polymers produced.

They may also affect the aqueous solution properties of alkali-swellable or alkali-soluble latex emulsions which may be either non-associative ASE , or associative by hydrophobe modification HASE. Using a constant HASE terpolymer composition, a study was conducted to examine the effects of twelve independent reaction variables on latex stability during processing reactor plating and grit formation , the final latex emulsion properties pH, particle size, viscosity and THF solubility dried polymer , and the aqueous solution properties upon neutralization viscosity, and clarity.

Rheology Modifiers

Some direct relationships observed with increasing component concentration were an increase in latex viscosity as a function of copolymerizable surfactant and an increase in latex and solution viscosity as a function of conventional surfactant. Among the inverse relationships observed with increasing component concentration were a decrease in reactor grit and plating as a function of copolymerizable surfactant and a decrease in aqueous solution viscosity as a function of crosslinking monomer and chain transfer agent.

The most surprising result observed which occurred in several variable sets was a relationship between aqueous solution thickening efficiency and a common dependent time variable start of continuous monomer addition relative to the observed exotherm peak during seed formation. Maximum solution viscosity was obtained when the timing of these events coincided. The advantages of blending a LCP with a thermoplastic polymer is that the LCP serves as a processing aid and can also form a reinforcing phase. Rheology plays an important role in determining the morphology and hence the mechanical properties of these blends.

Advanced Rheological Measurements Of Polymers & Rubber Compounds

This review also discusses the slow behavior of neat liquid crystalline polymers. The shear rate dependence is a function of molecular parameters sulfonation level, counterion, molecular weight and solvent polarity. The mechanism responsible for dilatancy is postulated to involve changes in the nature of associations under shear since solutions of non-associating polymers usually exhibit shear thinning behavior.

The influence of shear has also been explored with a new family of hydrocarbon soluble polymer complexes based on a combination of sulfonate ionomers and amine containing polymers. As compared with single ionomer solutions, such complexes offer much enhanced viscosities at low polymer concentrations, and visually dramatic dilatant solution behavior.

Potential mechanisms for this shear thickening behavior are also discussed. Polymers can modify not only a solution's shear and elongational viscosity, but its antimisting and drag reducing properties, as well. Associating polymers tend to be more potent solution rheology modifiers than conventional polymers.

This paper describes the synthesis and solution properties of associating functional alpha olefin polymers. Specifically, carboxyl associating polymers are prepared by a special Ziegler Natta polymerization method which overcomes catalyst poisoning. The carboxyl polymers can self associate via H-bonding or they can be titrated with Lewis base containing polymers e. The H-bonding polymers show enhanced shear and elongational viscosity compared with their nonfunctional counterparts.

They also exhibit shear thickening rheology and antimisting activity. In turn, the interpolymer complexes exhibit enhanced viscosity, shear thickening rheology and shear-stable drag reduction. Association polymers are water soluble polymers which can associate intermolecularly in solution. A series of association polymers was made by copolymerizing acrylamide with dodecylmethacrylate using a surfactant as emulsifier.

The solution properties were investigated by capillary viscometry, by using pyrene as a fluorescent probe, and by shear wave propagation. Experimental results indicated the presence of hydrophobic regions and association at all polymer concentrations.

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Above a critical hydrophobe concentration, a marked increase in the degree of association was apparent. Quantitative measurements of pyrene monomer and excimer fluorescence gave an average number of hydrophobes required to form a hydrophobic region as approximately This number was the same as the same as that calculated from a network model by applying the theory of rubber elasticity to the modulus obtained from shear wave propagation.

Nonionic hydrophobe-modified poly oxyethylene urethane HEUR associative thickeners have been designed possessing widely different but complementary viscosity-shear rate responses.



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