Characterizing the Structure of pH Dependent Polyelectrolyte Block Copolymer Micelles

We use fluorescence spectroscopy, dynamic light scattering (DLS), and small-angle neutron scattering (SANS) to characterize the structure of 2-(dimethylamino)ethyl methacrylate/2-(diethylamino)ethyl methacrylate (DMAEMA/DEAEMA) block copolymer micelles. The copolymers exhibit a strong pH dependence, where protonation of the tertiary amines along the side chains cause the blocks to be soluble in water. Fluorescence results show a critical degree of protonation below which single chains aggregate to form micelles. This critical degree of protonation depends on the copolymer concentration and solution ionic strength. Dynamic light scattering experiments provide unimer and micelle size distributions, and the measured critical degrees of protonation are consistent with the fluorescence data. The micelle hydrodynamic radius measured from DLS depends on the solution ionic strength, because of the polyelectrolyte nature of the protonated copolymers. Small-angle neutron scattering experiments in conjunction with a starlike micelle model provide additional insights into the micellar structures.