|Speciale i fysik og kemi, . modul, 2001, id:176|
|Findes på RUb:||ja|
This thesis contains investigations of the aggregation behavior of an ethylene oxide (EO), propylene oxide (PO), ethylene oxide (EO) triblock copolymer, P94, with the composion (EO)28(PO)48(EO)28. P94 has been studied in solutions of the chaotropic (water structure breaker) salt KSCN, and the cosmotropic (water structure builder) salt KF. The methods used are small angle x-ray scattering, capillary vicometry and rheology. A model has been constructed for the relationship between the macroscopic rheological properties and the microscopic interactions between P94 micelles, by assuming a simple repulsive exponential potential. The rheological measurements show that the transition temperatures for the hard gel phase, are shifted to higher temperatures, when KSCN is added to the solution. When KF is added, the same transition temperature is shifted to lower temperatures. These results are in accordance with the salts position in the so-called Hofmeister-series. Meassurements also show that both salts shift the critical gel concentration to P94 higher concentrations. Meassurements with a capillary viscometer show that the intrinsic viscosity is lowered when salts are added. This indicates taht these micelles have a more compact structure than in pure water. SAXS meassurements show that the aggregation number (number of inumers per micelle), is larger when KF is added to the solution, but smaller when KSCN is added. Scattering data also show that the estimated radius of the micelles is larger when KF added. The radius is a little smaller when KSCN is added, but the difference in radii between the micelles in a solution of KSCN and a solution without salt is very small. The model calculations make it possible to calculate the potential between the micelles, in the three types of solutions. When KSCN is added, the potential is higher at longer ranges, but the lope is smaller than the micelles in the solution without salt. When KF is added the potential at long ranges is smaller, but the lope is steeper. Meassurements indicate that when KF is added to a P94 solution, the micelles become more compact and their extension in water gets smaller. When KSCN is added, the picture is less clear. Meassurements show on one side that micelles are becomming more compact, but also that they have a longer range of extension in the solution. Thus the picture is not so clear with respect to the effect of KSCN.