Solution Rheological Properties

A further complication in understanding the rheology of hydrophobically associating polymers is the unique response to shear rate and solvent quality (e.g. salt content). As shown in Fig. 3.8, the viscosity can be independent (Newtonian), decrease (pseudoplastic) or even increase (dilatant) with shear rate depending on the polymer concentration and shear rate. As the hydrophobe level and polymer concentration increase beyond a critical value, a shear rate region in 

Surfactant macromonomers such as nonylphenoxypoly(etheroxy) acrylates, R-EO-Ac (Fig. 3.1), are water soluble or water dispersible. The extent of water solubility depends upon the hydrophile-lipophile balance (HLB) of the surfactant and the temperature. Surfactant monomers, wherein R = nonylphenyl and n = 10, 20, and 40 have been synthesized. 

Such surfomers can be easily copolymerized with acrylamide (AM) to form water soluble copolymers, i.e. poly(AM-co-R-EO-Ac), which contain low levels ( 5 mol %) of surfactant group. Unlike the copolymerization of acrylamide with other hydrophobic monomers (e.g. long chain alkylacrylamides), large amounts of external surfactant are not needed to solubilize the hydrophobic monomer. Rather, conventional free radical solution methods can be used to form high molecular weight copolymers [13]. 

Aqueous Solution Properties. Acrylamide copolymers containing even small quantities of surfomer units (i.e. 0.5 mol %) also exhibit interesting solution properties. For example, below C the surfomer copolymers show lower intrinsic viscosities rj and elevated Huggins constants, (Table 3.1). As with the RAM polymers, below C the chains interact intramolecularly to collapse the coil, lowering [rj ] and raising the slope of the reduced viscosity concentration plot, i.e. /ch [1 ]  

Above C these polymers show substantially higher viscosities than unsubstituted polyacrylamide. In this regime the viscosity depends upon the level and type of surfomer, as well as conventional polymerization variables, such as the ratio of monomer concentration to the square root of the initiator concentration, [M]/[I]. Of course, the [M]/[I] ratio is related to the degree of polymerization (DP) (or molecular weight M ) the polymer for an ideal free 

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Although a number of infrared bands can be used to establish that a micellar shape change has occurred, it is difficult to determine the actual shape unambiguously from the spectroscopic data alone. We therefore make use of micelle aggregation numbers and solution rheological properties, which depend on micelle size and shape, for correlation with the structural information (packing) provided by the FTIR spectra. 

Hydrophobic associations can dominate polymer conformation in solution and solution rheological properties. Intrinsic viscosity and Huggins interaction coefficients provided information on the conformation and intramolecular aggregation behavior of these polymers in dilute solution. The presence of hydrophobic associations caused a decrease in the intrinsic viscosity and an increase in the Huggins constant. These effects could be counterbalanced by increasing the ionic charge on the polymer through hydrolysis or by copolymerization with sodium acrylate. 

Solutions of rhamsan have high viscosity at low shear rates and low gum concentrations (90). The rheological properties and suspension capabiUty combined with excellent salt compatibihty, make it useful for several industrial apphcations including agricultural fertilizer suspensions, pigment suspensions, cleaners, and paints and coatings. 

Significant use properties of poly(ethylene oxide) are complete water solubiHty, low toxicity, unique solution rheology, complexation with organic acids, low ash content, and thermoplasticity. 

Starches. Starch (qv) granules must be cooked before they wiU release their water-soluble molecules. It is common to speak of solutions of polysaccharides, but in general, they do not form tme solutions because of their molecular sizes and intermolecular interactions rather they form molecular dispersions. The general rheological properties of polysaccharides like the starch polysaccharides are described below under the discussion of polysaccharides as water-soluble gums. Starch use permeates the entire economy because it (com starch in particular) is abundantly available and inexpensive. Another key factor to its widespread use is the fact that it occurs in the form of granules. 

One of the most common rubber adhesives are the contact adhesives. These adhesives are bonded by a diffusion process in which the adhesive is applied to both surfaces to be joined. To achieve optimum diffusion of polymer chains, two requirements are necessary (1) a high wettability of the adhesive by the smooth or rough substrate surfaces (2) adequate viscosity (in general rheological properties) of the adhesive to penetrate into the voids and roughness of the substrate surfaces. Both requirements can be easily achieved in liquid adhesives. Once the adhesive solution is applied on the surface of the substrate, spontaneous or forced evaporation of the solvent or water must be produced to obtain a dry adhesive film. In most cases, the dry-contact adhesive film contains residual solvent (about 5-10 wt%), which usually acts as a plasticizer. The time necessary... 

Xanthan does not in itself form gels, despite the strong intermolecular interactions which occur in solution. However, some of the rheological properties of xanthan have... 

Solutions of some polymeric materials also have similar rheological properties and behave in the same way as suspensions in pipe flow. However, they do in time break down and they do not give any appreciable increase in buoyancy as their densities differ little from that of water. 

The ionic strength dependence of intrinsic viscosity is function of molecular structure and protein folding, ft is well known that the conformational and rheological properties of charged biopolymer solutions are dependent not only upon electrostatic interactions between macromolecules but also upon interactions between biopolymer chains and mobile ions. Due electrostatic interactions the specific viscosity of extremely dilute solutions seems to increase infinitely with decreasing ionic concentration. Variations of the intrinsic viscosity of a charged polyampholite with ionic strength have problems of characterization. 

Taking into account the relevance of the range of semi-dilute solutions (in which intermolecular interactions and entanglements are of increasing importance) for industrial applications, a more detailed picture of the interrelationships between the solution structure and the rheological properties of these solutions was needed. The nature of entanglements at concentrations above the critical value c leads to the viscoelastic properties observable in shear flow experiments. The viscous part of the flow behaviour of a polymer in solution is usually represented by the zero-shear viscosity, rj0, which depends on the con-... 

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