Characterizing the structure of pH dependent polyelectrolyte block copolymer micelles

me use fluorescence spectroscopy, dynamic light scattering (DLS), and small -angle neutron scattering (SANS) to characterize the structure of 2-(dimeth ylamino)ethyl methacrylate/2-(diethylamino)ethyl methacrylate (DMAEMA/DEAEM A) block copolymer micelles. The copolymers exhibit a strong pH dependence, where protonation of the tertiary amines along the side chains cause the b locks to be soluble in water. Fluorescence results show a critical degree o f protonation below which single chains aggregate to form micelles. This cr itical degree of protonation depends on the copolymer concentration and sol ution ionic strength. Dynamic light scattering experiments provide unimer a nd micelle size distributions, and the measured critical degrees of protona tion are consistent with the fluorescence data. The micelle hydrodynamic ra dius measured from DLS depends on the solution ionic strength, because of t he polyelectrolyte nature of the protonated copolymers. Small-angle neutron scattering experiments in conjunction with a starlike micelle model provid e additional insights into the micellar structures.