Quantitatively Determining of Population Ratios in Bimodal Polymeric Solutions by Neutron Scattering*

Association of amphiphilic polymers in aqueous solutions is of fundamental importance. The coexistence of unimers and aggregates over a broad range of phase regions has been widely reported. Although scattering technique has been employed to identify the structure of micellar aggregates and free unimers as well as its time-evolution processes, the determination of their relative population of unimer and aggregate itself is still challenging. Here, using small angle neutron scattering, we present a comprehensive SANS study of n-dodecyl-PNIPAm. By adjusting the deuterium/hydrogen ratio of water, the intra-micellar polymer and water distributions are obtained. The micellar aggregation number and number density are further determined. Most importantly, the distributions of unimers and micellar aggregations at different temperatures are obtained quantitatively for the first time.