Characterizing Styrenic Triblock Copolymers Using Static Light Scattering

Light scattering refers to the process in which light hits a particle and scatters in a predictable pattern. This scattering pattern can be interpreted to understand the characteristics of the scattering particle. For this research, a measurement technique called static light scattering (SLS) was used, and due to the characteristics of the measurement setup and the size of particles in solution exclusively Rayleigh scattering is observed. SLS measures the standardized intensity of the scattering at multiple angles and multiple concentrations. This technique allows us to measure constants such as molecular weight, the A2 virial coefficient, and radius of gyration of the particles. Our focus was on characterizing styrenic block copolymers in order to understand the relationships between their molecular structure and their behavior in solution. The instrument used for these measurements is the BI-200SM Goniometer. Each applicable polymer was dissolved in chloroform, stirred overnight, and filtered prior to SLS analysis. Using the known weight concentrations of the solutions, and by measuring the scattered intensity at multiple angles of each concentration, we are able to organize the data into a Zimm plot. This Zimm plot allows constants related to the behavior of the polymers to be found in the slope of the trendlines of the measured data. Patterns between the known characteristics of these polymers and the newly measured constants allow a deeper understanding of the general solution behavior of these styrenic triblock copolymers. An important constant related to the particle's scattering behavior in solution is the refractive index increment. This increment was shown to be directly proportional to the styrene copolymer concentration. Another important finding was that the scaling of the measured radius of gyration with the measured molecular weight matches the expectation for a polymer in a good solvent. The main conclusion from the measured data is that you can effectively characterize styrenic triblock copolymers using static light scattering methods.