Polymer concentration effect rheological parameters

The rheological properties of a fluid interface may be characterized by four parameters surface shear viscosity and elasticity, and surface dilational viscosity and elasticity. When polymer monolayers are present at such interfaces, viscoelastic behavior has been observed (1,2), but theoretical progress has been slow. The adsorption of amphiphilic polymers at the interface in liquid emulsions stabilizes the particles mainly through osmotic pressure developed upon close approach. This has become known as steric stabilization (3,4.5). In this paper, the dynamic behavior of amphiphilic, hydrophobically modified hydroxyethyl celluloses (HM-HEC), was studied. In previous studies HM-HEC s were found to greatly reduce liquid/liquid interfacial tensions even at very low polymer concentrations, and were extremely effective emulsifiers for organic liquids in water (6). 

Rheological measurements were performed on xanthan solutions prepared by dilution of broths, 48(X) CX, A, C or powder Rhodopol 23, adjusted at similar polymer concentrations (between 5 and 7 g.l ). The effects of the addition of a protein-rich solution and of other parameters such as salinity and pH were further investigated. 

The polymers influence the rheological properties of fluids, due to acquiring a large volume in solution as compared to the total of the molecular dimensions of the repeating unite [3]. The solution volume occupied by the solvated polymer chain is known as the hydro-dynamic volume (HDV). The hydrodynamic volume is determined by polymer structural parameters (e.g., chain length and chain stifihiess), polymer-solvent interactions, polymer associations or repulsions, temperature, concentration, and molecular weight. The effective HDV of a random-coil polymer is generally equated to the product [ti]M defined by Flory [3] ... 

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