Structure investigation of poly((2-dimethylamino)ethyl methacrylate)/sodium dodecylsulfate complexes in concentrated poly((2-dimethylamino)ethyl methacrylate) solutions using small angle neutron scattering

The structure of poly((2-dimethylamino)ethyl methacrylate)/sodium dodecylsulfate complexes in water was investigated as a function of poly((2-dimethylamino)ethyl methacrylate) concentration at a fixed sodium dodecylsulfate concentration using small angle neutron scattering. When either hydrogenated or deuterated sodium dodecylsulfate was added to poly((2-dimethylamino)ethyl methacrylate) solutions in D2O, a peak was observed in the small angle neutron scattering which was characteristic of charged micelles. This peak shifted to higher q in both cases as poly((2-dimethylamino)ethyl methacrylate) concentration increased, indicating that the size and shape of micelles changed due to favorable interactions between poly((2-dimethylamino)ethyl methacrylate) and sodium dodecylsulfate. The small angle neutron scattering intensity of the micelles in the polymer/surfactant solutions was measured at the condition where poly((2-dimethylamino)ethyl methacrylate) was contrast-matched. It was possible to obtain information about the structure of the micelles using the Hayter-Penfold model. Based on the results from the fit of the SANS data, it was found that partial shielding provided by poly((2-dimethylamino)ethyl methacrylate) monomers being incorporated into the micelle shell significantly influenced both the form factor and the structure factor of micelles in the polymer/surfactant solutions. This led to a decrease in the micelle size and an increase in the number of micelles. It was found that any increased repulsive potential resulting from a smaller distance between the charged micelles was relieved by a decrease in the surface charge.