Investigation of polyacrylonitrile solution inhomogeneity by dynamic light scattering

Dynamic light scattering (DLS) has been used to quantify nanoscale heterogeneity in the industrially significant polyacrylonitrile (PAN) polymer solution. The heterogeneity in polymer solution, traced by the ratio of amplitudes of the slow to fast mode, is observed to be related to various parameters, such as molecular weight of the polymer, the type of co‐monomer, processing time, concentration of the solution, and the choice of the solvents. It has been identified that low molecular weight PAN homopolymer have the least heterogeneity issues. Amongst the chosen co‐polymers for this study, similar degree of heterogeneity was observed at concentration slightly above the critical concentration at which the polymer chains begin to overlap. Whereas, at higher concentration, PAN‐methacrylic acid (4 wt%) copolymer showed the least heterogeneity issue. The aggregate diffusion coefficient of PAN‐methacrylic acid (4 wt%) copolymer solution in dimethylformamide (DMF) and N , N ‐dimethylacetamide (DMAc) are respectively determined to be ∼1.6 × 10 −12 cm 2 /s and ∼1.6 × 10 −13 cm 2 /s, which results in an estimated aggregate size of 9 nm and 90 nm. POLYM. ENG. SCI., 55:1403–1407, 2015. © 2015 Society of Plastics Engineers