An unusual stress controlled turbulent flow phenomenon observed in aqueous solutions of some derivatives of an unsaturated 18 carbon atom fatty acid is described. Some other unusual viscometric and rheogoniometric properties of these solutions are also discussed.
The unique ability of certain macromolecules to reduce friction losses inturbulent duct flow has been amply demonstrated by a number of investigations, including among others. It has been suggested that this phenomenon of drag reduction is a direct consequence of viscoelastic behavior because the occurrence of markedly viscoelastic properties in solutions of certain macromolecules is characterized by the appearance of this unusual turbulent flow behavior. Recent measurements suggest that the reduced drag is a function of the ratio of elastic to viscous forces developed in these fluids. Tentative explanations put forth are based on a mode of elastic interaction between the dissolved macromolecules and the perturbed micromolecular solvent e.g., the strength of the drag reduction activity is determined by the time dependent processes or characteristic relaxation functions descriptive of the viscoelastic solution. All of the investigations of drag reduction in aqueous viscoelastic solutions involve so called "high polymers". Typical examples include synthetic polymers such as poly(acrylamides), poly(ethyleneoxides), and copolymer derivatives such as partially hydrolyzedpoly(acrylonitriles). A variety of naturally occurring polymeric substances are also characterized by the property of drag reduction, including guar gum, and the sodium salt of alginic acid.
It is generally agreed that when a high polymer dissolves, depending upon the concentration, some fraction of these macromolecules form a loose three-dimensional network. The networks and localized junctions can apparently arise for a number of reasons, e.g., as a result of a distribution of inter-and intramolecular forces, gross physical entanglements, disturbances of the flow field, and perhaps combinations of these and other effects.
viscoelastic surfactant
