

@mastersthesis {7296,
	title = {Rheological changes with solvent conditions in entangled polyelectrolyte solutions},
	year = {2010},
	note = {0822587},
	school = {Colorado School of Mines},
	type = {phdPh.{D}.},
	address = {Ann Arbor},
	abstract = {High molecular weight polyelectrolytes are commonly used as drag reducers, viscosity enhancers, and drilling fluids. An understanding of polyelectrolyte solution rheology under various solvent conditions is critical to their efficient use in industry. Polyelectrolyte concentrations ranging from dilute to concentrated in both water and salt solution are studied using oscillatory and shear rheology. In salt free solution, the scaling of xanthan viscosity is found to agree well with predictions. Critical concentrations marking changes in the viscosity scaling behavior are determined in water and in 50 mM NaCl. The viscosity of xanthan decreases significantly upon addition of NaCl for concentrations in the semidilute unentangled regime. However, for xanthan concentrations above cD , the zero shear rate viscosity (as well as the magnitude of the dynamic moduli) increases significantly in the presence of salt. Similar increases in viscosity upon addition of salt are measured for several other high molecular weight polyelectrolytes (HPAM, PAA, Carrageenan, Welan). The effects of the size and charge of added salt counterions on both the shear and oscillatory rheology of polyelectrolyte solutions are also examined. Regardless of valency, the normalized viscosity increases with increasing ionic radius of the salt counterion. For counterions of similar ionic radius and differing valency, the counterion carrying the higher charge produces a higher viscosity. Further, addition of NiCl 2 to entangled xanthan solutions results in a stable gel at 25{\textdegree}C. The kinetics of the gelation and the rheological properties of several gels are examined. Hypotheses are developed to explain the dependence of viscosity increase on counterion size and valency and the gelation in the presence of NiCl 2 . In a turbulent pipe flow, significant drag reduction is measured for xanthan concentrations as low as 20 ppm. Drag reduction effectiveness is greatly increased when an entangled xanthan solution is diluted to a concentration in the dilute regime. The increased drag reduction effectiveness is hypothesized to be attributed to residual entanglements and network structure present in the diluted solution. Rheological measurements show that diluted solutions exhibit greater elasticity than solutions prepared at the dilute concentration, in agreement with the proposed theory.},
	keywords = {0542:Chemical engineering, Applied sciences, Chemical engineering, Drag reduction, Polyelectrolyte solutions, Xanthan},
	url = {http://search.proquest.com/docview/748827582?accountid=14270},
	author = {Wyatt, Nicholas B.}
}
