Small angle neutron scattering (SANS) studies of a conjugated polyelectrolyte in aqueous solution

Small angle neutron scattering (SANS) by the conjugated polyelectrolyte, poly[5-methoxy-2-(4-sulfobutoxy)-1,4-phenylene-vinylene], was studied in semi-dilute solutions. A broad peak appears at high momentum transfer (q) for all concentrations. The peak position (qm) and intensity (I(qm)) scale with polymer concentration as qm∼c1/2 and I(qm)/c∼c−1/2, consistent with polyelectrolyte theory. The upturn of I(q) at q<0.08 Å−1 indicates chain aggregation. Addition of excess salt removes the broad peak from I(q). In high-salt solutions, I(q)∼q−1 implying a rod-like conformation with a persistence length larger than 800 Å.