Alkyl chain length and headgroup dependent stability and agglomeration properties of surfactant-assisted colloidal selenium nanoparticles

In this study, we have systematically investigated and reported the growth, stability, and aggregation properties of selenium nanoparticles (Se NPs) in the presence of surfactant systems comprising different head groups and alkyl chain lengths. Here, the n-alkyl sulfates (C10-C14) and n-alkyl trimethylammonium bromides (C12-C18) were used as the anionic and cationic surfactants. The obtained results showed that the shortening in the alkyl chain length both in anionic and cationic groups does not affect the Se NPs morphologically, however it leads to a gradual increase in their mean sizes. It was also found that the surfactants having a cationic head group pave the way for forming the bigger NPs compared to the anionic ones. In addition, especially in the cationic group, the NPs were found to be in an increasing aggregation tendency with decreasing number of carbon atoms in the chain length. On the other hand, it was observed that the absorbance tends to decrease with time both in the anionic and cationic systems. The rate of decrease in the absorbance within the time revealed that the elongation in the alkyl chain length gives rise to a more stable nanoparticle solution for both surfactant systems. Further-more, the results revealed that the surfactants having an anionic head group kept the Se NPs more stable in their solutions as compared to cationic ones. The scanning electron microscopy images corresponding to absorption measurements taken for certain days suggested that the formation of aggregated structures, which increase along with time in the nanoparticle solution, is responsible for the accelerated decrease in the absorbance as the tail length decreases.