Effects of organic solvents on the scission energy of rodlike micelles.
The linear viscoelastic response of erucyl bis(hydroxyethyl) methylammonium chloride with added KCl has been studied as a function of temperature and nonpolar solvent addition. The plateau modulus is independent of temperature from 25 to 40 degrees C, in contrast to previous studies with salicylate counterions that showed a plateau modulus increasing with temperature over this range. The average micelle length, L, predicted by the model of Cates, depends experimentally on Escis/kBT, where Escis is the scission energy of the chain and kBT is the Boltzmann constant times the absolute temperature. With ethanol addition, the calculated average contour length, L, decreases by a factor of 4 as ethanol concentration varies from 0 to 1.3 M. This corresponds to an apparent energy for scission, Escis, decrease from 81 +/- 8 to 74 +/- 7 kJ/mol. On the other hand, only 80 mM of hexane is required to cause a decrease in Escis to the same level, and for hexane addition levels above 70 mM a disruption in the plateau modulus indicates the disruption of the rodlike structure. The correspondence between the effect of temperature and the effect of solvent addition allows the development of "solvent/temperature" superposition rules to predict the rheology of these viscoelastic fluids at elevated temperatures.
Siriwatwechakul
Wanwipa
W
Chemical Engineering Department, Princeton University, Princeton, New Jersey 08544, USA.
Lafleur
Terry
T
Prud'homme
Robert K
RK
Sullivan
Phillip
P
D004548:Elasticity; D004735:Energy Transfer; D004883:Erucic Acids / Q000737:chemistry*; D000431:Ethanol / Q000737:chemistry*; D006586:Hexanes / Q000737:chemistry*; D008823:Micelles; D000644:Quaternary Ammonium Compounds / Q000737:chemistry*; D012212:Rheology; D013696:Temperature
D004883:Erucic Acids; D006586:Hexanes; D008823:Micelles; D000644:Quaternary Ammonium Compounds; C509663:erucyl bis(hydroxyethyl) methylammonium chloride; D000431:Ethanol