A Light-Scattering Study of the Aggregation Behavior of Fluorocarbon-Modified Polyacrylamides in Water

Fluorocarbon-modified polyacrylamide chains can form large multichain aggregates. The aggregation behavior of a series of fluorocarbon-modified polyacrylamides in water has been investigated by a combination of static and dynamic laser light scattering (LLS). The critical aggregation concentration (CAC) was estimated from the emergence of a second peak in the line-width distribution measured in dynamic LLS. Our results showed that CAC strongly depends on the amount of 2-(N-ethylperfluorooctanesulfonamido)ethyl acrylate (FX-13) copolymerized with polyacrylamide and also on the polymer concentration. When the FX-13 content is 0.227 mol %, CAC is as low as 1.34 × 10-4 g/mL, while when the FX-13 content is less than 0.028 mol %, no aggregation has been observed over the entire concentration range studied. A combination of the weight-average molecular weight from static LLS and the area ratio of the two peaks in the line-width distribution from dynamic LLS leads us to the estimation that on average each aggregate consists of ∼5-9 individual polymer chains for the acrylamide copolymer with 0.227 mol % FX-13. The solution contained 40 wt % of the multichain aggregates when the polymer concentration was higher than the CAC. On the other hand, the intensity ratio of the light scattered from the multichain aggregates over that from individual chains increased linearly with increasing polymer concentration.