Scattering Studies of Macromolecules in Solution

The sphere-to-rod transition of nonionic micelles of the PEO-PPO-PEO triblock copolymer P123 and the surfactant C12EO6 was studied using dynamic and static light scattering, small angel X-ray scattering, rheology and calorimetry. The transition temperature was dependent of the C12EO6/P123 molar ratio, which means that a larger content of C12EO6 yields a higher transition temperature. Furthermore, at temperature below the shape transition, the size of the spherical mixed micelles decreases with increasing C12EO6 content, which explains the increased transition temperature. Namely, smaller spheres have a higher curvature and demand more energy to change into a rodlike shape. The sphere-to-rod transition revealed a very strong concentration dependence, which was found with DLS and SLS and confirmed with rheology. It was found with SLS that the intermicellar interaction was dependent on the molar ratio. At low molar ratio, interaction was explained by hard-sphere interaction while at higher molar ratio the interaction followed the group renormalization theory for polymer-like structures. SAXS measurements were carried out on the same system with the aim to study the internal structure and shape of the mixed micelles. It was found that the inhomogeneities that were established from the pair distance distribution functions increase with increasing molar ratio, which revealed that the C12EO6 molecules are located in the junction between PPO (core) and PEO (corona) part of the P123 micelles.

The time-resolved DLS method used in the P123-C12EO6 micellar project was also employed in the study of a bacterial virus system. The DNA ejection from bacteriophage lambda was studied simultaneously with DLS and SLS under different physical conditions. A model was constructed from which the relation between the DLS and SLS data was explained. The temperature dependence was studied and the rate of ejection increased when the temperature was increased. The rate was also dependent of the length of DNA inside the virus capsid. It was also shown that additives such as DNA-binding proteins (HU and DNase) not only increased the rate of ejection but also full-filled the ejection.