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

Abstract

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.